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HCR_EL2, Hypervisor Configuration Register

The HCR_EL2 characteristics are:

Purpose

Provides configuration controls for virtualization, including defining whether various operations are trapped to EL2.

Configuration

AArch64 System register HCR_EL2 bits [31:0] are architecturally mapped to AArch32 System register HCR[31:0] .

AArch64 System register HCR_EL2 bits [63:32] are architecturally mapped to AArch32 System register HCR2[31:0] .

If EL2 is not implemented, this register is RES0 from EL3.

This register has no effect if EL2 is not enabled in the current Security state.

RW fields in this register reset to architecturally UNKNOWN values.

Attributes

HCR_EL2 is a 64-bit register.

Field descriptions

The HCR_EL2 bit assignments are:

Bits [63:59]

Reserved, RES0.

TID5, bit [58]

When ARMv8.5-MemTag is implemented:

Trap ID group 5. Traps the following register accesses to EL2, when EL2 is enabled in the current Security state:

AArch64:

TID5Meaning
0b0

This control does not cause any instructions to be trapped.

0b1

The specified EL1 and EL0 accesses to ID group 5 registers are trapped to EL2.

When the value of HCR_EL2.{E2H, TGE} is {1, 1}, this field has an Effective value of 0 for all purposes other than a direct read of the value of this bit.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

DCT, bit [57]

When ARMv8.5-MemTag is implemented:

Default Cacheability Tagging. When HCR_EL2.DC is in effect, controls whether addresses are Tagged or Untagged.

DCTMeaning
0b0

Addresses are Untagged.

0b1

Addresses are Tagged.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

ATA, bit [56]

When ARMv8.5-MemTag is implemented:

Allocation Tag Access. When SCR_EL3.ATA=1 and HCR_EL2.{E2H,TGE} != {1,1}, controls EL1 and EL0 access to Allocation Tags.

When access is prevented:

  • Instructions which Load or Store data are Unchecked.

  • Instructions which Load or Store Allocation Tags treat the Allocation Tag as RAZ/WI.

  • Instructions which insert Logical Address Tags into addresses treat the Allocation Tag used to generate the Logical Address Tag as 0.

  • Cache maintenance instructions which invalidate Allocation Tags from caches behave as the equivalent Clean and Invalidate operation on Allocation Tags.

  • MRS and MSR instructions at EL1 using GCR_EL1, RGSR_EL1, TFSR_EL1, TFSR_EL2, or TFSRE0_EL1 that are not UNDEFINED are trapped to EL2.

ATAMeaning
0b0

Access is prevented.

0b1

Access is not prevented.

This field is permitted to be cached in a TLB.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

TTLBOS, bit [55]

When ARMv8.2-EVT is implemented:

Trap TLB maintenance instructions that operate on the Outer Shareable domain. Traps execution of those TLB maintenance instructions at EL1 using AArch64 to EL2 when EL2 is enabled in the current Security state. This applies to the following instructions:

TLBI VMALLE1OS, TLBI VAE1OS, TLBI ASIDE1OS,TLBI VAAE1OS, TLBI VALE1OS, TLBI VAALE1OS,TLBI RVAE1OS, TLBI RVAAE1OS,TLBI RVALE1OS, and TLBI RVAALE1OS.

TTLBOSMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

Execution of the specified instructions are trapped to EL2.

If ARMv8.2-EVT is not implemented, this field is RES0.

When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this field behaves as 0 for all purposes other than a direct read of the value of this bit.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

TTLBIS, bit [54]

When ARMv8.2-EVT is implemented:

Trap TLB maintenance instructions that operate on the Inner Shareable domain. Traps execution of those TLB maintenance instructions at EL1 using AArch64, and at EL1 using AArch32, to EL2 when EL2 is enabled in the current Security state. This applies to the following instructions:

TTLBISMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

Execution of the specified instructions are trapped to EL2.

If ARMv8.2-EVT is not implemented, this field is RES0.

When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this field behaves as 0 for all purposes other than a direct read of the value of this bit.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

EnSCXT, bit [53]

When ARMv8.0-CSV3 is implemented:

Enable Access to the SCXTNUM_EL1 and SCXTNUM_EL0 registers. The defined values are:

EnSCXTMeaning
0b0

When (HCR_EL2.TGE==0 or HCR_EL2.E2H==0) and EL2 is enabled in the current Security state , EL1 and EL0 access to SCXTNUM_EL0 and EL1 access to SCXTNUM_EL1 is disabled by this mechanism, causing an exception to EL2, and the values of these registers to be treated as 0.

When ((HCR_EL2.TGE==1 and HCR_EL2.E2H==1) and EL2 is enabled in the current Security state , EL0 access to SCXTNUM_EL0 is disabled by this mechanism, causing an exception to EL2, and the value of this register to be treated as 0.

0b1

This control does not cause accesses to SCXTNUM_EL0 or SCXTNUM_EL1 to be trapped.

When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1,1}, this bit has no effect on execution at EL0.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

TOCU, bit [52]

When ARMv8.2-EVT is implemented:

Trap cache maintenance instructions that operate to the Point of Unification. Traps execution of those cache maintenance instructions at EL1 or EL0 using AArch64, and at EL1 using AArch32, to EL2 when EL2 is enabled in the current Security state. This applies to the following instructions:

Note

An exception generated because an instruction is UNDEFINED at EL0 is higher priority than this trap to EL2. In addition:

TOCUMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

Execution of the specified instructions are trapped to EL2.

If ARMv8.2-EVT is not implemented, this field is RES0.

If the Point of Unification is before any level of data cache, it is IMPLEMENTATION DEFINED whether the execution of any data or unified cache clean by VA to the Point of Unification instruction can be trapped when the value of this control is 1.

If the Point of Unification is before any level of instruction cache, it is IMPLEMENTATION DEFINED whether the execution of any instruction cache invalidate to the Point of Unification instruction can be trapped when the value of this control is 1.

When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this field behaves as 0 for all purposes other than a direct read of the value of this bit.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

Bit [51]

Reserved, RES0.

TICAB, bit [50]

When ARMv8.2-EVT is implemented:

Trap ICIALLUIS/IC IALLUIS cache maintenance instructions. Traps execution of those cache maintenance instructions at EL1 using AArch64, and at EL1 using AArch32, to EL2 when EL2 is enabled in the current Security state. This applies to the following instructions:

TICABMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

EL1 execution of the specified instructions is trapped to EL2.

If ARMv8.2-EVT is not implemented, this field is RES0.

If the Point of Unification is before any level of instruction cache, it is IMPLEMENTATION DEFINED whether the execution of any instruction cache invalidate to the Point of Unification instruction can be trapped when the value of this control is 1.

When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this field behaves as 0 for all purposes other than a direct read of the value of this bit.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

TID4, bit [49]

When ARMv8.2-EVT is implemented:

Trap ID group 4. Traps the following register accesses to EL2, when EL2 is enabled in the current Security state:

AArch64:

AArch32:

TID4Meaning
0b0

This control does not cause any instructions to be trapped.

0b1

The specified EL1 and EL0 accesses to ID group 4 registers are trapped to EL2.

If ARMv8.2-EVT is not implemented, this field is RES0.

When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this field behaves as 0 for all purposes other than a direct read of the value of this bit.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

Bit [48]

Reserved, RES0.

FIEN, bit [47]

When ARMv8.4-RAS is implemented:

Fault Injection Enable. Unless this bit is set to 1, accesses to the ERXPFGCDN_EL1, ERXPFGCTL_EL1, and ERXPFGF_EL1 registers from EL1 generate a Trap exception to EL2, when EL2 is enabled in the current Security state.

FIENMeaning
0b0

Accesses to the specified registers from EL1 are trapped to EL2, when EL2 is enabled in the current Security state.

0b1

This control does not cause any instructions to be trapped.

If EL2 is disabled in the current Security state, the Effective value of HCR_EL2.FIEN is 0b1.

If ERRIDR_EL1.NUM is zero, meaning no error records are implemented, or no error record accessible using System registers is owned by a node that implements the RAS Common Fault Injection Model Extension, then this bit might be RES0.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

FWB, bit [46]

When ARMv8.4-S2FWB is implemented:

Defines the combined cacheability attributes in a 2 stage translation regime.

FWBMeaning
0b0

When this bit is 0, then:

  • The combination of stage 1 and stage 2 translations on memory type and cacheability attributes are as described in the Armv8.0 architecture. For more information see D4.5.4 Combining the stage 1 and stage 2 attributes

  • The encoding of the stage 2 memory type and cacheability attributes in bits[5:2] of the stage 2 page or block descriptors are as described in the Armv8.0 architecture.

0b1

When this bit is 1, then:

  • Bit[5] of stage 2 page or block descriptor is RES0.

  • When bit[4] of stage 2 page or block descriptor is 1 and when:

    • Bits[3:2] of stage 2 page or block descriptor are 0b11, the resultant memory type and inner or outer cachebility attribute is the same as the stage 1 memory type and inner or outer cacheability attribute.

    • Bits[3:2] of stage 2 page or block descriptor are 0b10, the resultant memory type and attribute is Normal Write-Back.

    • Bits[3:2] of stage 2 page or block descriptor are 0b0x, the resultant memory type will be Normal Non-cacheable except where the stage 1 memory type was Device->attr< the resultant memory type will be Device->attr<

  • When bit[4] of stage 2 page or block descriptor is 0 the memory type is Device, and when:

    • Bits[3:2] of stage 2 page or block descriptor are 0b00, the resultant memory type is Device-nGnRnE.

    • Bits[3:2] of stage 2 page or block descriptor are 0b01, the resultant memory type is Device-nGnRE.

    • Bits[3:2] of stage 2 page or block descriptor are 0b10, the resultant memory type is Device-nGRE.

    • Bits[3:2] of stage 2 page or block descriptor are 0b11, the resultant memory type is Device-GRE.

  • If the stage 1 translation specifies a cacheable memory type, then the stage 1 cache allocation hint is applied to the final cache allocation hint where the final memory type is cacheable.

  • If the stage 1 translation does not specify a cacheable memory type, then if the final memory type is cacheable, it is treated as read allocate, write allocate.

In Secure state, this bit applies to both the Secure stage 2 translation and the Non-secure stage 2 translation.

This bit is permitted to be cached in a TLB.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

NV2, bit [45]

When ARMv8.4-NV is implemented:

Nested Virtualization. Changes the behaviors of HCR_EL2.{NV, NV1} to provide a mechanism for hardware to transform reads and writes from System registers into reads and writes from memory.

NV2Meaning
0b0

This bit has no effect on the behavior of HCR_EL2.{NV, NV1}.

0b1

Redefines behavior of HCR_EL2{NV, NV1} to enable:

  • Transformation of read/writes to registers into read/writes to memory.
  • Redirection of EL2 registers to EL1 registers.

When this bit is 0, the behavior of HCR_EL2.{NV, NV1} is as defined for ARMv8.3-NV.

When this is bit is 1, then any exception taken from EL1 and taken to EL1 causes SPSR_EL1.M[3:2] to be set to 0b10 and not 0b01

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

AT, bit [44]

When ARMv8.3-NV is implemented:

Address Translation. EL1 execution of the following address translation instructions is trapped to EL2, when EL2 is enabled in the current Security state:

AT S1E0R, AT S1E0W, AT S1E1R, AT S1E1W, AT S1E1RP, AT S1E1WP

ATMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

EL1 execution of the specified instructions is trapped to EL2.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

NV1, bit [43]

When ARMv8.4-NV is implemented:

Nested Virtualization.

NV1Meaning
0b0

If HCR_EL2.{NV, NV2} are both 1, accesses executed from EL1 to implemented EL12, EL02, or EL2 registers are transformed to loads and stores.

If HCR_EL2.NV2 is 0 or HCR_EL2.{NV, NV2} == {0, 1}, this control does not cause any instructions to be trapped.

0b1

If HCR_EL2.NV2 is 1, accesses executed from EL1 to implemented EL2 registers are transformed to loads and stores.

If HCR_EL2.NV2 is 0, EL1 accesses to VBAR_EL1, ELR_EL1, and SPSR_EL1, are trapped to EL2, when EL2 is enabled in the current Security state.

If HCR_EL2.NV2 is 1, the value of HCR_EL2.NV1 defines which EL1 register accesses are transformed to loads and stores. These transformed accesses have priority over the trapping of registers.

The trapping of EL1 registers caused by other control bits has priority over the transformation of these accesses.

If a register is specified that is not implemented by an implementation, then access to that register is treated as unallocated.

For the list of registers affected, see Enhanced support for nested virtualization.

If HCR_EL2.{NV, NV1, NV2} are {1, 0, 0},any exception taken from EL1, and taken to EL1, causes the SPSR_EL1.M[3:2] to be set to 0b10, and not 0b01.

If HCR_EL2.{NV, NV1, NV2} are {1, 1, 0}, then:

  • The EL1 translation table Block and Page descriptors:
    • Bit[54] holds the PXN instead of the UXN.
    • Bit[53] is RES0.
    • Bit[6] is treated as 0 regardless of the actual value.
  • If Hierarchical Permissions are enabled, the EL1 translation table Table descriptors are as follows:
    • Bit[61] is treated as 0 regardless of the actual value.
    • Bit[60] holds the PXNTable instead of the UXNTable.
    • Bit[59] is RES0.
  • When executing at EL1, the PSTATE.PAN bit is treated as zero for all purposes except reading the value of the bit.
  • When executing at EL1, the LDTR* instructions are treated as the equivalent LDR* instructions, and the STTR* instructions are treated as the equivalent STR* instructions.

If HCR_EL2.{NV, NV1, NV2} are {0, 1, 0}, then the behavior is a CONSTRAINED UNPREDICTABLE choice of:

  • Behaving as if HCR_EL2.NV is 1 and HCR_EL2.NV1 is 1 for all purposes other than reading than reading back the value of the HCR_EL2.NV bit.
  • Behaving as if HCR_EL2.NV is 0 and HCR_EL2.NV1 is 0 for all purposes other than reading than reading back the value of the HCR_EL2.NV1 bit.
  • Behaving with regard to the HCR_EL2.NV and HCR_EL2.NV1 bits behavior as defined in the rest of this description.

This bit is permitted to be cached in a TLB.

This field resets to an architecturally UNKNOWN value.


When ARMv8.3-NV is implemented:

Nested Virtualization. EL1 accesses to certain registers are trapped to EL2, when EL2 is enabled in the current Security state.

NV1Meaning
0b0

This control does not cause any instructions to be trapped.

0b1

EL1 accesses to VBAR_EL1, ELR_EL1, SPSR_EL1 are trapped to EL2, when EL2 is enabled in the current Security state.

If HCR_EL2.NV is 1 and HCR_EL2.NV1 is 0 then the following effects also apply:

  • Any exception taken from EL1, and taken to EL1, causes the SPSR_EL1.M[3:2] to be set to 0b10, and not 0b01.

If the bits HCR_EL2.NV and HCR_EL2.NV1 are both set to 1 then following effects also apply:

  • The EL1 translation table Block and Page descriptors:
    • Bit[54] holds the PXN instead of the UXN.
    • Bit[53] is RES0.
    • Bit[6] is treated as 0 regardless of the actual value.
  • If Hierarchical Permissions are enabled, the EL1 translation table Table descriptors are as follows:
    • Bit[61] is treated as 0 regardless of the actual value.
    • Bit[60] holds the PXNTable instead of the UXNTable.
    • Bit[59] is RES0.
  • When executing at EL1, the PSTATE.PAN bit is treated as zero for all purposes except reading the value of the bit.
  • When executing at EL1, the LDTR* instructions are treated as the equivalent LDR* instructions, and the STTR* instructions are treated as the equivalent STR* instructions.

If HCR_EL2.NV is 0 and HCR_EL2.NV1 is 1 then the behavior is a CONSTRAINED UNPREDICTABLE choice of:

  • Behaving as if HCR_EL2.NV is 1 and HCR_EL2.NV1 is 1 for all purposes other than reading than reading back the value of the HCR_EL2.NV bit.
  • Behaving as if HCR_EL2.NV is 0 and HCR_EL2.NV1 is 0 for all purposes other than reading than reading back the value of the HCR_EL2.NV1 bit.
  • Behaving with regard to the HCR_EL2.NV and HCR_EL2.NV1 bits behavior as defined in the rest of this description.

This bit is permitted to be cached in a TLB.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

NV, bit [42]

When ARMv8.4-NV is implemented:

Nested Virtualization.

When HCR_EL2.NV2 is 1, redefines register accesses so that:

When HCR_EL2.NV2 is 0, or if ARMv8.4-NV is not implemented, traps functionality that is permitted at EL2 and would be UNDEFINED at EL1 if this field was 0, when EL2 is enabled in the current Security state. This applies to the following operations:

  • EL1 accesses to Special-purpose registers that are not UNDEFINED at EL2.
  • EL1 accesses to System registers that are not UNDEFINED at EL2.
  • Execution of EL1 or EL2 translation regime address translation and TLB maintenance instructions for EL2 and above.
NVMeaning
0b0

When this bit is set to 0, HCR_EL2.NV2 == 0 for all purposes other than reading this register. This control does not cause any instructions to be trapped.

When HCR_EL2.NV2 is 1, no ARMv8.4-NV functionality is implemented.

0b1

When HCR_EL2.NV2 is 0, or if ARMv8.4-NV is not implemented, EL1 accesses to the specified registers or the execution of the specified instructions are trapped to EL2, when EL2 is enabled in the current Security state. EL1 read accesses to the CurrentEL register return a value of 0x2.

When HCR_EL2.NV2 is 1, this control redefines EL1 register accesses so that instructions accessing SPSR_EL2, ELR_EL2, ESR_EL2, and FAR_EL2 instead access SPSR_EL1, ELR_EL1, ESR_EL1, and FAR_EL1 respectively.

When HCR_EL2.NV2 is 0, or if ARMv8.4-NV is not implemented, then:

  • The System or Special-purpose registers for which accesses are trapped are as follows:
    • Registers accessed using MRS or MSR with a name ending in _EL2.
    • Registers accessed using MRS or MSR with a name ending in _EL12.
    • Registers accessed using MRS or MSR with a name ending in _EL02.
    • Special-purpose registers SPSR_irq, SPSR_abt, SPSR_und and SPSR_fiq, accessed using MRS or MSR.
    • Special-purpose register SP_EL1 accessed using the dedicated MRS or MSR instruction.
  • The instructions for which the execution is trapped are as follows:
    • EL2 translation regime Address Translation instructions and TLB maintenance instructions.
    • EL1 translation regime Address Translation instructions and TLB maintenance instructions that are only accessible from EL2 and EL3.
    • SMC in an implementation that does not include EL3 and when HCR_EL2.TSC is 1. HCR_EL2.TSC bit is not RES0 in this case.
    • The ERET, ERETAA, and ERETAB instructions.
Note

The priority of this trap is higher than the priority of the HCR_EL2.API trap. If both of these bits are set so that EL1 execution of an ERETAA or ERETAB instruction is trapped to EL2, then the syndrome reported is 0x1A.

This field resets to an architecturally UNKNOWN value.


When ARMv8.3-NV is implemented:

Nested Virtualization. Traps functionality that is permitted at EL2 and would be UNDEFINED at EL1 if this field was 0, when EL2 is enabled in the current Security state. This applies to the following operations:

  • EL1 accesses to Special-purpose registers that are not UNDEFINED at EL2.
  • EL1 accesses to System registers that are not UNDEFINED at EL2.
  • Execution of EL1 or EL2 translation regime address translation and TLB maintenance instructions for EL2 and above.

The possible values are:

NVMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

EL1 accesses to the specified registers or the execution of the specified instructions are trapped to EL2, when EL2 is enabled in the current Security state. EL1 read accesses to the CurrentEL register return a value of 0x2.

The System or Special-purpose registers for which accesses are trapped are as follows:

  • Registers accessed using MRS or MSR with a name ending in _EL2.
  • Registers accessed using MRS or MSR with a name ending in _EL12.
  • Registers accessed using MRS or MSR with a name ending in _EL02.
  • Special-purpose registers SPSR_irq, SPSR_abt, SPSR_und and SPSR_fiq, accessed using MRS or MSR.
  • Special-purpose register SP_EL1 accessed using the dedicated MRS or MSR instruction.

The instructions for which the execution is trapped are as follows:

  • EL2 translation regime Address Translation instructions and TLB maintenance instructions.
  • EL1 translation regime Address Translation instructions and TLB maintenance instructions that are only accessible from EL2 and EL3.
  • The ERET, ERETAA, and ERETAB instructions.
Note

The priority of this trap is higher than the priority of the HCR_EL2.API trap. If both of these bits are set so that EL1 execution of an ERETAA or ERETAB instruction is trapped to EL2, then the syndrome reported is 0x1A.

  • SMC in an implementation that does not include EL3 and when HCR_EL2.TSC is 1. HCR_EL2.TSC bit is not RES0 in this case.

This bit is permitted to be cached in a TLB.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

API, bit [41]

When ARMv8.3-PAuth is implemented:

Controls the use of instructions related to Pointer Authentication:

  • PACGA.
  • AUTDA, AUTDB, AUTDZA, AUTDZB, AUTIA, AUTIA1716, AUTIASP, AUTIAZ, AUTIB, AUTIB1716, AUTIBSP, AUTIBZ, AUTIZA, AUTIZB, PACDA, PACDB, PACDZA, PACDZB, PACIA, PACIA1716, PACIASP, PACIAZ, PACIB, PACIB1716, PACIBSP, PACIBZ, PACIZA, PACIZ, RETAA, RETAB, BRAA, BRAB, BLRAA, BLRAB, BRAAZ, BRABZ, BLRAAZ, BLRABZ, ERETAA, ERETAB, LDRAA and LDRAB when:
    • In EL0, when HCR_EL2.TGE==0 or HCR_EL2.E2H==0, and the associated SCTLR_EL1.En<N><M>==1.
    • In EL1, the associated SCTLR_EL1.En<N><M>==1.
APIMeaning
0b0

The instructions related to Pointer Authentication are trapped to EL2, when EL2 is enabled in the current Security state and the instructions are enabled for the EL1&0 translation regime, from:

  • EL0 when HCR_EL2.TGE==0 or HCR_EL2.E2H==0.

  • EL1.

If HCR_EL2.NV is 1, the HCR_EL2.NV trap takes precedence over the HCR_EL2.API trap for the ERETAA and ERETAB instructions.

0b1

This control does not cause any instructions to be trapped.

If ARMv8.3-PAuth is implemented but EL2 is not implemented or disabled in the current Security state, the system behaves as if this bit is 1.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

APK, bit [40]

When ARMv8.3-PAuth is implemented:

Trap registers holding "key" values for Pointer Authentication. Traps accesses to the following registers from EL1 to EL2, when EL2 is enabled in the current Security state:

APKMeaning
0b0

Access to the registers holding "key" values for pointer authentication from EL1 are trapped to EL2, when EL2 is enabled in the current Security state.

0b1

This control does not cause any instructions to be trapped.

Note

If ARMv8.3-PAuth is implemented but EL2 is not implemented or is disabled in the current Security state, the system behaves as if this bit is 1.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

TME, bit [39]

When TME is implemented:

Enables access to the TSTART, TCOMMIT, TTEST and TCANCEL instructions at EL0 and EL1.

TMEMeaning
0b0

EL0 and EL1 accesses to TSTART, TCOMMIT, TTEST and TCANCEL instructions are UNDEFINED.

0b1

This control does not cause any instruction to be UNDEFINED.

If EL2 is not implemented or is disabled in the current Security state, the Effective value of this bit is 0b1.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

MIOCNCE, bit [38]

Mismatched Inner/Outer Cacheable Non-Coherency Enable, for the EL1&0 translation regimes.

MIOCNCEMeaning
0b0

For the EL1&0 translation regimes, for permitted accesses to a memory location that use a common definition of the Shareability and Cacheability of the location, there must be no loss of coherency if the Inner Cacheability attribute for those accesses differs from the Outer Cacheability attribute.

0b1

For the EL1&0 translation regimes, for permitted accesses to a memory location that use a common definition of the Shareability and Cacheability of the location, there might be a loss of coherency if the Inner Cacheability attribute for those accesses differs from the Outer Cacheability attribute.

For more information see 'Mismatched memory attributes' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile, section B2 (The AArch64 Application Level Memory Model).

This field can be implemented as RAZ/WI.

When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, the PE ignores the value of this field for all purposes other than a direct read of this field.

This field resets to an architecturally UNKNOWN value.

TEA, bit [37]

Route synchronous External abort exceptions to EL2. If the RAS Extension is implemented, the possible values of this bit are:

TEAMeaning
0b0

This control does not cause exceptions to be routed from EL0 and EL1 to EL2.

0b1

Route synchronous External abort exceptions from EL0 and EL1 to EL2, when EL2 is enabled in the current Security state, if not routed to EL3.

When the RAS Extension is not implemented, this field is RES0.

This field resets to an architecturally UNKNOWN value.

TERR, bit [36]

When RAS is implemented:

Trap Error record accesses. Trap accesses to the following registers from EL1 to EL2:

EL1 using AArch64: ERRIDR_EL1, ERRSELR_EL1, ERXADDR_EL1, ERXCTLR_EL1, ERXFR_EL1, ERXMISC0_EL1, ERXMISC1_EL1, and ERXSTATUS_EL1. When ARMv8.4-RAS is implemented, ERXMISC2_EL1, and ERXMISC3_EL1.

EL1 using AArch32: ERRIDR, ERRSELR, ERXADDR, ERXADDR2, ERXCTLR, ERXCTLR2, ERXFR, ERXFR2, ERXMISC0, ERXMISC1, ERXMISC2, ERXMISC3, and ERXSTATUS. When ARMv8.4-RAS is implemented, ERXMISC4, ERXMISC5, ERXMISC6, and ERXMISC7.

TERRMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

Accesses to the specified registers from EL1 generate a Trap exception to EL2, when EL2 is enabled in the current Security state.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

TLOR, bit [35]

From Armv8.1:

Trap LOR registers. Traps accesses to the LORSA_EL1, LOREA_EL1, LORN_EL1, LORC_EL1, and LORID_EL1 registers from EL1 to EL2, when EL2 is enabled in the current Security state.

TLORMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

EL1 accesses to the LOR registers are trapped to EL2, when EL2 is enabled in the current Security state.

When HCR_EL2.TGE is 1, the PE ignores the value of this field for all purposes other than a direct read of this field.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

E2H, bit [34]

From Armv8.1:

EL2 Host. Enables a configuration where a Host Operating System is running in EL2, and the Host Operating System's applications are running in EL0.

E2HMeaning
0b0

The facilities to support a Host Operating System at EL2 are disabled.

0b1

The facilities to support a Host Operating System at EL2 are enabled.

For information on the behavior of this bit see Behavior of HCR_EL2.E2H.

This bit is permitted to be cached in a TLB.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

ID, bit [33]

Stage 2 Instruction access cacheability disable. For the EL1&0 translation regime, when EL2 is enabled in the current Security state and HCR_EL2.VM==1, this control forces all stage 2 translations for instruction accesses to Normal memory to be Non-cacheable.

IDMeaning
0b0

This control has no effect on stage 2 of the EL1&0 translation regime.

0b1

Forces all stage 2 translations for instruction accesses to Normal memory to be Non-cacheable.

This bit has no effect on the EL2, EL2&0, or EL3 translation regimes.

When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, the PE ignores the value of this field for all purposes other than a direct read of this field.

This field resets to an architecturally UNKNOWN value.

CD, bit [32]

Stage 2 Data access cacheability disable. For the EL1&0 translation regime, when EL2 is enabled in the current Security state and HCR_EL2.VM==1, this control forces all stage 2 translations for data accesses and translation table walks to Normal memory to be Non-cacheable.

CDMeaning
0b0

This control has no effect on stage 2 of the EL1&0 translation regime for data accesses and translation table walks.

0b1

Forces all stage 2 translations for data accesses and translation table walks to Normal memory to be Non-cacheable.

This bit has no effect on the EL2, EL2&0, or EL3 translation regimes.

When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, the PE ignores the value of this field for all purposes other than a direct read of this field.

This field resets to an architecturally UNKNOWN value.

RW, bit [31]

Execution state control for lower Exception levels:

RWMeaning
0b0

Lower levels are all AArch32.

0b1

The Execution state for EL1 is AArch64. The Execution state for EL0 is determined by the current value of PSTATE.nRW when executing at EL0.

If AArch32 state is not supported by the implementation at EL1, then this bit is RAO/WI.

In an implementation that includes EL3, when EL2 is not enabled in Secure state, the PE behaves as if this bit has the same value as the SCR_EL3.RW bit for all purposes other than a direct read or write access of HCR_EL2.

The RW bit is permitted to be cached in a TLB.

When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this field behaves as 1 for all purposes other than a direct read of the value of this bit.

This field resets to an architecturally UNKNOWN value.

TRVM, bit [30]

Trap Reads of Virtual Memory controls. Traps EL1 reads of the virtual memory control registers to EL2, when EL2 is enabled in the current Security state, from both Execution states. The registers for which read accesses are trapped are as follows:

EL1 using AArch64: SCTLR_EL1, TTBR0_EL1, TTBR1_EL1, TCR_EL1, ESR_EL1, FAR_EL1, AFSR0_EL1, AFSR1_EL1, MAIR_EL1, AMAIR_EL1, CONTEXTIDR_EL1.

EL1 using AArch32: SCTLR, TTBR0, TTBR1, TTBCR, TTBCR2, DACR, DFSR, IFSR, DFAR, IFAR, ADFSR, AIFSR, PRRR, NMRR, MAIR0, MAIR1, AMAIR0, AMAIR1, CONTEXTIDR.

TRVMMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

EL1 read accesses to the specified Virtual Memory controls are trapped to EL2, when EL2 is enabled in the current Security state.

When HCR_EL2.TGE is 1, the PE ignores the value of this field for all purposes other than a direct read of this field.

This field resets to an architecturally UNKNOWN value.

HCD, bit [29]

HVC instruction disable. Disables EL1 execution of HVC instructions, from both Execution states, when EL2 is enabled in the current Security state.

HCDMeaning
0b0

HVC instruction execution is enabled at EL2 and EL1.

0b1

HVC instructions are UNDEFINED at EL2 and EL1. Any resulting exception is taken to the Exception level at which the HVC instruction is executed.

Note

HVC instructions are always UNDEFINED at EL0.

This bit is only implemented if EL3 is not implemented. Otherwise, it is RES0.

When HCR_EL2.TGE is 1, the PE ignores the value of this field for all purposes other than a direct read of this field.

This field resets to an architecturally UNKNOWN value.

TDZ, bit [28]

Trap DC ZVA instructions. Traps EL0 and EL1 execution of DC ZVA instructions to EL2, when EL2 is enabled in the current Security state, from AArch64 state only.

If ARMv8.5-MemTag is implemented, this trap also applies to DC GVA and DC GZVA.

TDZMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

In AArch64 state, any attempt to execute an instruction this trap applies to at EL1, or at EL0 when the instruction is not UNDEFINED at EL0, is trapped to EL2 when EL2 is enabled in the current Security state.

Reading the DCZID_EL0 returns a value that indicates that the instructions this trap applies to are not supported.

When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this field behaves as 0 for all purposes other than a direct read of the value of this bit.

This field resets to an architecturally UNKNOWN value.

TGE, bit [27]

Trap General Exceptions, from EL0.

TGEMeaning
0b0

This control has no effect on execution at EL0.

0b1

When EL2 is not enabled in the current Security state, this control has no effect on execution at EL0.

When EL2 is enabled in the current Security state, in all cases:

  • All exceptions that would be routed to EL1 are routed to EL2.
  • The SCTLR_EL1.M field, or the SCTLR.M field if EL1 is using AArch32, is treated as being 0 for all purposes other than returning the result of a direct read of SCTLR_EL1 or SCTLR.
  • All virtual interrupts are disabled.
  • Any IMPLEMENTATION DEFINED mechanisms for signaling virtual interrupts are disabled.
  • An exception return to EL1 is treated as an illegal exception return.
  • The MDCR_EL2.{TDRA, TDOSA, TDA, TDE} fields are treated as being 1 for all purposes other than returning the result of a direct read of MDCR_EL2.

In addition, when EL2 is enabled in the current Security state, if:

  • HCR_EL2.E2H is 0, the Effective values of the HCR_EL2.{FMO, IMO, AMO} fields are 1.
  • HCR_EL2.E2H is 1, the Effective values of the HCR_EL2.{FMO, IMO, AMO} fields are 0.

For further information on the behavior of this bit when E2H is 1, see Behavior of HCR_EL2.E2H.

HCR_EL2.TGE must not be cached in a TLB.

This field resets to an architecturally UNKNOWN value.

TVM, bit [26]

Trap Virtual Memory controls. Traps EL1 writes to the virtual memory control registers to EL2, when EL2 is enabled in the current Security state, from both Execution states. The registers for which write accesses are trapped are as follows:

EL1 using AArch64: SCTLR_EL1, TTBR0_EL1, TTBR1_EL1, TCR_EL1, ESR_EL1, FAR_EL1, AFSR0_EL1, AFSR1_EL1, MAIR_EL1, AMAIR_EL1, CONTEXTIDR_EL1.

EL1 using AArch32: SCTLR, TTBR0, TTBR1, TTBCR, TTBCR2, DACR, DFSR, IFSR, DFAR, IFAR, ADFSR, AIFSR, PRRR, NMRR, MAIR0, MAIR1, AMAIR0, AMAIR1, CONTEXTIDR.

TVMMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

EL1 write accesses to the specified EL1 virtual memory control registers are trapped to EL2, when EL2 is enabled in the current Security state.

When HCR_EL2.TGE is 1, the PE ignores the value of this field for all purposes other than a direct read of this field.

This field resets to an architecturally UNKNOWN value.

TTLB, bit [25]

When ARMv8.4-TLBI is implemented:

Trap TLB maintenance instructions. Traps EL1 execution of TLB maintenance instructions to EL2, when EL2 is enabled in the current Security state, from both Execution states. This applies to the following instructions:

TTLBMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

EL1 execution of the specified TLB maintenance instructions are trapped to EL2, when EL2 is enabled in the current Security state.

When HCR_EL2.TGE is 1, the PE ignores the value of this field for all purposes other than a direct read of this field.

This field resets to an architecturally UNKNOWN value.


From Armv8.0:

Trap TLB maintenance instructions. Traps EL1 execution of TLB maintenance instructions to EL2, when EL2 is enabled in the current Security state, from both Execution states. This applies to the following instructions:

TTLBMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

EL1 execution of the specified TLB maintenance instructions are trapped to EL2, when EL2 is enabled in the current Security state.

When HCR_EL2.TGE is 1, the PE ignores the value of this field for all purposes other than a direct read of this field.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

TPU, bit [24]

Trap cache maintenance instructions that operate to the Point of Unification. Traps execution of those cache maintenance instructions at EL1 or EL0 using AArch64, and at EL1 using AArch32, to EL2 when EL2 is enabled in the current Security state. This applies to the following instructions:

Note

An exception generated because an instruction is UNDEFINED at EL0 is higher priority than this trap to EL2. In addition:

TPUMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

Execution of the specified instructions is trapped to EL2, when EL2 is enabled in the current Security state.

If the Point of Unification is before any level of data cache, it is IMPLEMENTATION DEFINED whether the execution of any data or unified cache clean by VA to the Point of Unification instruction can be trapped when the value of this control is 1.

If the Point of Unification is before any level of instruction cache, it is IMPLEMENTATION DEFINED whether the execution of any instruction cache invalidate to the Point of Unification instruction can be trapped when the value of this control is 1.

When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this field behaves as 0 for all purposes other than a direct read of the value of this bit.

This field resets to an architecturally UNKNOWN value.

TPCP, bit [23]

When ARMv8.2-DCPoP is implemented:

Trap data or unified cache maintenance instructions that operate to the Point of Coherency or Persistence. Traps execution of those cache maintenance instructions at EL1 or EL0 using AArch64, and at EL1 using AArch32, to EL2 when EL2 is enabled in the current Security state. This applies to the following instructions:

If ARMv8.2-DCCVADP is implemented, this trap also applies to DC CVADP.

If ARMv8.5-MemTag is implemented, this trap also applies to DC CIGVAC, DC CIGDVAC, DC IGVAC, DC IGDVAC, DC CGVAC, DC CGDVAC, DC CGVAP and DC CGDVAP.

If ARMv8.2-DCCVADP and ARMv8.5-MemTag are implemented, this trap also applies to DC CGVADP and DC CGDVADP.

Note
  • An exception generated because an instruction is UNDEFINED at EL0 is higher priority than this trap to EL2. In addition:
    • AArch64 instructions which invalidate by VA to the Point of Coherency are always UNDEFINED at EL0 using AArch64.
    • DCIMVAC, DCCIMVAC, and DCCMVAC are always UNDEFINED at EL0 using AArch32.
  • In Armv8.0 this field is named TPC. From Armv8.2 it is named TPCP.
TPCPMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

Execution of the specified instructions is trapped to EL2, when EL2 is enabled in the current Security state.

If the Point of Coherency is before any level of data cache, it is IMPLEMENTATION DEFINED whether the execution of any data or unified cache clean, invalidate, or clean and invalidate instruction that operates by VA to the point of coherency can be trapped when the value of this control is 1.

If HCR_EL2.{E2H, TGE} is set to {1, 1}, this field behaves as 0 for all purposes other than a direct read of the value of this bit.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Trap data or unified cache maintenance instructions that operate to the Point of Coherency. Traps execution of those cache maintenance instructions at EL1 or EL0 using AArch64, and at EL1 using AArch32, to EL2 when EL2 is enabled in the current Security state. This applies to the following instructions:

Note
  • An exception generated because an instruction is UNDEFINED at EL0 is higher priority than this trap to EL2. In addition:
    • AArch64 instructions which invalidate by VA to the Point of Coherency are always UNDEFINED at EL0 using AArch64.
    • DCIMVAC, DCCIMVAC, and DCCMVAC are always UNDEFINED at EL0 using AArch32.
  • In Armv8.0 this field is named TPC. From Armv8.2 it is named TPCP.
TPCMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

Execution of the specified instructions is trapped to EL2, when EL2 is enabled in the current Security state.

If the Point of Coherency is before any level of data cache, it is IMPLEMENTATION DEFINED whether the execution of any data or unified cache clean, invalidate, or clean and invalidate instruction that operates by VA to the point of coherency can be trapped when the value of this control is 1.

When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this field behaves as 0 for all purposes other than a direct read of the value of this bit.

This field resets to an architecturally UNKNOWN value.

TSW, bit [22]

Trap data or unified cache maintenance instructions that operate by Set/Way. Traps execution of those cache maintenance instructions at EL1 using AArch64, and at EL1 using AArch32, to EL2 when EL2 is enabled in the current Security state. This applies to the following instructions:

If ARMv8.5-MemTag is implemented, this trap also applies to DC IGSW, DC IGDSW, DC CGSW, DC CGDW, DC CIGSW, and DC CIGDSW.

Note

An exception generated because an instruction is UNDEFINED at EL0 is higher priority than this trap to EL2, and these instructions are always UNDEFINED at EL0.

TSWMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

Execution of the specified instructions is trapped to EL2, when EL2 is enabled in the current Security state.

When HCR_EL2.TGE is 1, the PE ignores the value of this field for all purposes other than a direct read of this field.

This field resets to an architecturally UNKNOWN value.

TACR, bit [21]

Trap Auxiliary Control Registers. Traps EL1 accesses to the Auxiliary Control Registers to EL2, when EL2 is enabled in the current Security state, from both Execution states. This applies to the following register accesses:

TACRMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

EL1 accesses to the specified registers are trapped to EL2, when EL2 is enabled in the current Security state.

When HCR_EL2.TGE is 1, the PE ignores the value of this field for all purposes other than a direct read of this field.

This field resets to an architecturally UNKNOWN value.

TIDCP, bit [20]

Trap IMPLEMENTATION DEFINED functionality. Traps EL1 accesses to the encodings reserved for IMPLEMENTATION DEFINED functionality to EL2, when EL2 is enabled in the current Security state. This applies to the following register accesses:

AArch64: The following reserved encoding spaces:

  • IMPLEMENTATION DEFINED System instructions, which are accessed using SYS and SYSL, with CRn == {11, 15}.
  • IMPLEMENTATION DEFINED System registers, which are accessed using MRS and MSR with the S3_<op1>_<Cn>_<Cm>_<op2> register name.

AArch32: MCR and MRC instructions accessing the following encodings:

  • All coproc==p15, CRn==c9, opc1 == {0-7}, CRm == {c0-c2, c5-c8}, opc2 == {0-7}.
  • All coproc==p15, CRn==c10, opc1 =={0-7}, CRm == {c0, c1, c4, c8}, opc2 == {0-7}.
  • All coproc==p15, CRn==c11, opc1=={0-7}, CRm == {c0-c8, c15}, opc2 == {0-7}.

When the value of HCR_EL2.TIDCP is 1, it is IMPLEMENTATION DEFINED whether any of this functionality accessed from EL0 is trapped to EL2. If it is not, then it is UNDEFINED, and any attempt to access it from EL0 generates an exception that is taken to EL1.

TIDCPMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

EL1 accesses to or execution of the specified encodings reserved for IMPLEMENTATION DEFINED functionality are trapped to EL2, when EL2 is enabled in the current Security state.

This field resets to an architecturally UNKNOWN value.

TSC, bit [19]

Trap SMC instructions. Traps EL1 execution of SMC instructions to EL2, when EL2 is enabled in the current Security state, from both Execution states.

TSCMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

If EL3 is implemented, then any attempt to execute an SMC instruction at EL1 using AArch64 or EL1 using AArch32 is trapped to EL2, when EL2 is enabled in the current Security state, regardless of the value of SCR_EL3.SMD.

If EL3 is not implemented, ARMv8.3-NV is implemented, and HCR_EL2.NV is 1, then any attempt to execute an SMC instruction at EL1 using AArch64 is trapped to EL2, when EL2 is enabled in the current Security state.

In AArch32 state, the Armv8-A architecture permits, but does not require, this trap to apply to conditional SMC instructions that fail their condition code check, in the same way as with traps on other conditional instructions.

If EL3 is not implemented, and HCR_EL2.NV is 0, this bit is RES0.

When HCR_EL2.TGE is 1, the PE ignores the value of this field for all purposes other than a direct read of this field.

This field resets to an architecturally UNKNOWN value.

TID3, bit [18]

Trap ID group 3. Traps EL1 reads of the following registers to EL2, when EL2 is enabled in the current Security state:

AArch64: ID_PFR0_EL1, ID_PFR1_EL1, ID_DFR0_EL1, ID_AFR0_EL1, ID_MMFR0_EL1, ID_MMFR1_EL1, ID_MMFR2_EL1, ID_MMFR3_EL1, ID_ISAR0_EL1, ID_ISAR1_EL1, ID_ISAR2_EL1, ID_ISAR3_EL1, ID_ISAR4_EL1, ID_ISAR5_EL1, ID_ISAR6_EL1, MVFR0_EL1, MVFR1_EL1, MVFR2_EL1, ID_AA64PFR0_EL1, ID_AA64PFR1_EL1, ID_AA64DFR0_EL1, ID_AA64DFR1_EL1, ID_AA64ISAR0_EL1, ID_AA64ISAR1_EL1, ID_AA64MMFR0_EL1, ID_AA64MMFR1_EL1, ID_AA64MMFR2_EL1, ID_AA64AFR0_EL1, ID_AA64AFR1_EL1, ID_AA64ZFR0_EL1 (where SVE is implemented), and ID_MMFR4_EL1, except that if ID_MMFR4_EL1 is implemented as RAZ/WI then it is IMPLEMENTATION DEFINED whether accesses to ID_MMFR4_EL1 are trapped.

It is IMPLEMENTATION DEFINED whether this field traps MRS accesses to encodings in the following range that are not already mentioned in this field description:

  • Op0 == 3, op1 == 0, CRn == c0, CRm == {c2-c7}, op2 == {0-7}.

AArch32: ID_PFR0, ID_PFR1, ID_DFR0, ID_AFR0, ID_MMFR0, ID_MMFR1, ID_MMFR2, ID_MMFR3, ID_ISAR0, ID_ISAR1, ID_ISAR2, ID_ISAR3, ID_ISAR4, ID_ISAR5, MVFR0, MVFR1, MVFR2, and ID_MMFR4, except that if ID_MMFR4 is implemented as RAZ/WI then it is IMPLEMENTATION DEFINED whether accesses to ID_MMFR4 are trapped.

MRC access to any of the following encodings are also trapped:

  • coproc==p15, opc1 == 0, CRn == c0, CRm == {c3-c7}, opc2 == {0,1}.
  • coproc==p15, opc1 == 0, CRn == c0, CRm == c3, opc2 == 2.
  • coproc==p15, opc1 == 0, CRn == c0, CRm == c5, opc2 == {4,5}.

It is IMPLEMENTATION DEFINED whether this bit traps MRC accesses to the following encodings:

  • coproc==p15, opc1 == 0, CRn == c0, CRm == c2, opc2 == 7.
  • coproc==p15, opc1 == 0, CRn == c0, CRm == c3, opc2 == {3-7}.
  • coproc==p15, opc1 == 0, CRn == c0, CRm == {c4, c6, c7}, opc2 == {2-7}.
  • coproc==p15, opc1 == 0, CRn == c0, CRm == c5, opc2 == {2, 3, 6, 7}.
TID3Meaning
0b0

This control does not cause any instructions to be trapped.

0b1

The specified EL1 read accesses to ID group 3 registers are trapped to EL2, when EL2 is enabled in the current Security state.

When HCR_EL2.TGE is 1, the PE ignores the value of this field for all purposes other than a direct read of this field.

This field resets to an architecturally UNKNOWN value.

TID2, bit [17]

Trap ID group 2. Traps the following register accesses to EL2, when EL2 is enabled in the current Security state:

AArch64:

AArch32:

TID2Meaning
0b0

This control does not cause any instructions to be trapped.

0b1

The specified EL1 and EL0 accesses to ID group 2 registers are trapped to EL2, when EL2 is enabled in the current Security state.

When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this field behaves as 0 for all purposes other than a direct read of the value of this bit.

This field resets to an architecturally UNKNOWN value.

TID1, bit [16]

Trap ID group 1. Traps EL1 reads of the following registers to EL2, when EL2 is enabled in the current Security state:

AArch64: REVIDR_EL1, AIDR_EL1.

AArch32: TCMTR, TLBTR, REVIDR, AIDR.

TID1Meaning
0b0

This control does not cause any instructions to be trapped.

0b1

The specified EL1 read accesses to ID group 1 registers are trapped to EL2, when EL2 is enabled in the current Security state.

When HCR_EL2.TGE is 1, the PE ignores the value of this field for all purposes other than a direct read of this field.

This field resets to an architecturally UNKNOWN value.

TID0, bit [15]

Trap ID group 0. Traps the following register accesses to EL2:

AArch64: None.

AArch32:

  • EL1 reads of the JIDR.
  • If the JIDR is RAZ from EL0, EL0 reads of the JIDR.
  • EL1 reads of the FPSID.
Note
  • It is IMPLEMENTATION DEFINED whether the JIDR is RAZ or UNDEFINED at EL0. If it is UNDEFINED at EL0 then any resulting exception takes precedence over this trap.
  • The FPSID is not accessible at EL0 using AArch32.
  • Writes to the FPSID are ignored, and not trapped by this control.
TID0Meaning
0b0

This control does not cause any instructions to be trapped.

0b1

The specified EL1 read accesses to ID group 0 registers are trapped to EL2, when EL2 is enabled in the current Security state.

In an AArch64 only implementation, this bit is RES0.

When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this field behaves as 0 for all purposes other than a direct read of the value of this bit.

This field resets to an architecturally UNKNOWN value.

TWE, bit [14]

Traps EL0 and EL1 execution of WFE instructions to EL2, when EL2 is enabled in the current Security state, from both Execution states.

TWEMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

Any attempt to execute a WFE instruction at EL0 or EL1 is trapped to EL2, when EL2 is enabled in the current Security state, if the instruction would otherwise have caused the PE to enter a low-power state and it is not trapped by SCTLR.nTWE or SCTLR_EL1.nTWE.

In AArch32 state, the attempted execution of a conditional WFE instruction is only trapped if the instruction passes its condition code check.

Note

Since a WFE can complete at any time, even without a Wakeup event, the traps on WFE are not guaranteed to be taken, even if the WFE is executed when there is no Wakeup event. The only guarantee is that if the instruction does not complete in finite time in the absence of a Wakeup event, the trap will be taken.

When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this field behaves as 0 for all purposes other than a direct read of the value of this bit.

This field resets to an architecturally UNKNOWN value.

TWI, bit [13]

Traps EL0 and EL1 execution of WFI instructions to EL2, when EL2 is enabled in the current Security state, from both Execution states.

TWIMeaning
0b0

This control does not cause any instructions to be trapped.

0b1

Any attempt to execute a WFI instruction at EL0 or EL1 is trapped to EL2, when EL2 is enabled in the current Security state, if the instruction would otherwise have caused the PE to enter a low-power state and it is not trapped by SCTLR.nTWI or SCTLR_EL1.nTWI.

In AArch32 state, the attempted execution of a conditional WFI instruction is only trapped if the instruction passes its condition code check.

Note

Since a WFI can complete at any time, even without a Wakeup event, the traps on WFI are not guaranteed to be taken, even if the WFI is executed when there is no Wakeup event. The only guarantee is that if the instruction does not complete in finite time in the absence of a Wakeup event, the trap will be taken.

When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this field behaves as 0 for all purposes other than a direct read of the value of this bit.

This field resets to an architecturally UNKNOWN value.

DC, bit [12]

Default Cacheability.

DCMeaning
0b0

This control has no effect on the EL1&0 translation regime.

0b1

In both Security states:

  • When EL1 is using AArch64, the PE behaves as if the value of the SCTLR_EL1.M field is 0 for all purposes other than returning the value of a direct read of SCTLR_EL1.
  • When EL1 is using AArch32, the PE behaves as if the value of the SCTLR.M field is 0 for all purposes other than returning the value of a direct read of SCTLR.
  • The PE behaves as if the value of the HCR_EL2.VM field is 1 for all purposes other than returning the value of a direct read of HCR_EL2.
  • The memory type produced by stage 1 of the EL1&0 translation regime is Normal Non-Shareable, Inner Write-Back Read-Allocate Write-Allocate, Outer Write-Back Read-Allocate Write-Allocate.

This field has no effect on the EL2, EL2&0, and EL3 translation regimes.

This field is permitted to be cached in a TLB.

When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this field behaves as 0 for all purposes other than a direct read of the value of this field.

This field resets to an architecturally UNKNOWN value.

BSU, bits [11:10]

Barrier Shareability upgrade. This field determines the minimum shareability domain that is applied to any barrier instruction executed from EL1 or EL0:

BSUMeaning
0b00

No effect.

0b01

Inner Shareable.

0b10

Outer Shareable.

0b11

Full system.

This value is combined with the specified level of the barrier held in its instruction, using the same principles as combining the shareability attributes from two stages of address translation.

When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this field behaves as 0b00 for all purposes other than a direct read of the value of this bit.

This field resets to an architecturally UNKNOWN value.

FB, bit [9]

Force broadcast. Causes the following instructions to be broadcast within the Inner Shareable domain when executed from EL1:

AArch32: BPIALL, TLBIALL, TLBIMVA, TLBIASID, DTLBIALL, DTLBIMVA, DTLBIASID, ITLBIALL, ITLBIMVA, ITLBIASID, TLBIMVAA, ICIALLU, TLBIMVAL, TLBIMVAAL.

AArch64: TLBI VMALLE1, TLBI VAE1, TLBI ASIDE1, TLBI VAAE1, TLBI VALE1, TLBI VAALE1, IC IALLU, TLBI RVAE1, TLBI RVAAE1, TLBI RVALE1, TLBI RVAALE1.

FBMeaning
0b0

This field has no effect on the operation of the specified instructions.

0b1

When one of the specified instruction is executed at EL1, the instruction is broadcast within the Inner Shareable shareability domain.

When HCR_EL2.TGE is 1, the PE ignores the value of this field for all purposes other than a direct read of this field.

This field resets to an architecturally UNKNOWN value.

VSE, bit [8]

Virtual SError interrupt.

VSEMeaning
0b0

This mechanism is not making a virtual SError interrupt pending.

0b1

A virtual SError interrupt is pending because of this mechanism.

The virtual SError interrupt is only enabled when the value of HCR_EL2.{TGE, AMO} is {0, 1}.

This field resets to an architecturally UNKNOWN value.

VI, bit [7]

Virtual IRQ Interrupt.

VIMeaning
0b0

This mechanism is not making a virtual IRQ pending.

0b1

A virtual IRQ is pending because of this mechanism.

The virtual IRQ is enabled only when the value of HCR_EL2.{TGE, IMO} is {0, 1}.

This field resets to an architecturally UNKNOWN value.

VF, bit [6]

Virtual FIQ Interrupt.

VFMeaning
0b0

This mechanism is not making a virtual FIQ pending.

0b1

A virtual FIQ is pending because of this mechanism.

The virtual FIQ is enabled only when the value of HCR_EL2.{TGE, FMO} is {0, 1}.

This field resets to an architecturally UNKNOWN value.

AMO, bit [5]

Physical SError interrupt routing.

AMOMeaning
0b0

When executing at Exception levels below EL2, and EL2 is enabled in the current Security state:

  • Physical SError interrupts are not taken to EL2.
  • When the value of HCR_EL2.TGE is 0, if the PE is executing at EL2 using AArch64, physical SError interrupts are not taken unless they are routed to EL3 by the SCR_EL3.EA bit.
  • Virtual SError interrupts are disabled.
0b1

When executing at any Exception level, and EL2 is enabled in the current Security state:

  • Physical SError interrupts are taken to EL2, unless they are routed to EL3.
  • When the value of HCR_EL2.TGE is 0, then virtual SError interrupts are enabled.

If EL2 is enabled in the current Security state and the value of HCR_EL2.TGE is 1:

  • Regardless of the value of the AMO bit physical asynchronous External aborts and SError interrupts target EL2 unless they are routed to EL3.
  • When ARMv8.1-VHE is not implemented, or if HCR_EL2.E2H is 0, this field behaves as 1 for all purposes other than a direct read of the value of this bit.
  • When ARMv8.1-VHE is implemented and HCR_EL2.E2H is 1, this field behaves as 0 for all purposes other than a direct read of the value of this bit.

For more information, see 'Asynchronous exception routing' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile, section D1 (The AArch64 System Level Programmers' Model).

This field resets to an architecturally UNKNOWN value.

IMO, bit [4]

Physical IRQ Routing.

IMOMeaning
0b0

When executing at Exception levels below EL2, and EL2 is enabled in the current Security state:

  • Physical IRQ interrupts are not taken to EL2.
  • When the value of HCR_EL2.TGE is 0, if the PE is executing at EL2 using AArch64, physical IRQ interrupts are not taken unless they are routed to EL3 by the SCR_EL3.IRQ bit.
  • Virtual IRQ interrupts are disabled.
0b1

When executing at any Exception level, and EL2 is enabled in the current Security state:

  • Physical IRQ interrupts are taken to EL2, unless they are routed to EL3.
  • When the value of HCR_EL2.TGE is 0, then Virtual IRQ interrupts are enabled.

If EL2 is enabled in the current Security state, and the value of HCR_EL2.TGE is 1:

  • Regardless of the value of the IMO bit, physical IRQ Interrupts target EL2 unless they are routed to EL3.
  • When ARMv8.1-VHE is not implemented, or if HCR_EL2.E2H is 0, this field behaves as 1 for all purposes other than a direct read of the value of this bit.
  • When ARMv8.1-VHE is implemented and HCR_EL2.E2H is 1, this field behaves as 0 for all purposes other than a direct read of the value of this bit.

For more information, see 'Asynchronous exception routing' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile, section D1.

This field resets to an architecturally UNKNOWN value.

FMO, bit [3]

Physical FIQ Routing.

FMOMeaning
0b0

When executing at Exception levels below EL2, and EL2 is enabled in the current Security state:

  • Physical FIQ interrupts are not taken to EL2.
  • When the value of HCR_EL2.TGE is 0, if the PE is executing at EL2 using AArch64, physical FIQ interrupts are not taken unless they are routed to EL3 by the SCR_EL3.FIQ bit.
  • Virtual FIQ interrupts are disabled.
0b1

When executing at any Exception level, and EL2 is enabled in the current Security state:

  • Physical FIQ interrupts are taken to EL2, unless they are routed to EL3.
  • When HCR_EL2.TGE is 0, then Virtual FIQ interrupts are enabled.

If EL2 is enabled in the current Security state and the value of HCR_EL2.TGE is 1:

  • Regardless of the value of the FMO bit, physical FIQ Interrupts target EL2 unless they are routed to EL3.
  • When ARMv8.1-VHE is not implemented, or if HCR_EL2.E2H is 0, this field behaves as 1 for all purposes other than a direct read of the value of this bit.
  • When ARMv8.1-VHE is implemented and HCR_EL2.E2H is 1, this field behaves as 0 for all purposes other than a direct read of the value of this bit.

For more information, see 'Asynchronous exception routing' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile, section D1.

This field resets to an architecturally UNKNOWN value.

PTW, bit [2]

Protected Table Walk. In the EL1&0 translation regime, a translation table access made as part of a stage 1 translation table walk is subject to a stage 2 translation. The combining of the memory type attributes from the two stages of translation means the access might be made to a type of Device memory. If this occurs, then the value of this bit determines the behavior:

PTWMeaning
0b0

The translation table walk occurs as if it is to Normal Non-cacheable memory. This means it can be made speculatively.

0b1

The memory access generates a stage 2 Permission fault.

This field is permitted to be cached in a TLB.

When HCR_EL2.TGE is 1, the PE ignores the value of this field for all purposes other than a direct read of this field.

This field resets to an architecturally UNKNOWN value.

SWIO, bit [1]

Set/Way Invalidation Override. Causes EL1 execution of the data cache invalidate by set/way instructions to perform a data cache clean and invalidate by set/way:

SWIOMeaning
0b0

This control has no effect on the operation of data cache invalidate by set/way instructions.

0b1

Data cache invalidate by set/way instructions perform a data cache clean and invalidate by set/way.

When the value of this bit is 1:

AArch32: DCISW performs the same invalidation as a DCCISW instruction.

AArch64: DC ISW performs the same invalidation as a DC CISW instruction.

This bit can be implemented as RES1.

When HCR_EL2.TGE is 1, the PE ignores the value of this field for all purposes other than a direct read of this field.

This field resets to an architecturally UNKNOWN value.

VM, bit [0]

Virtualization enable. Enables stage 2 address translation for the EL1&0 translation regime, when EL2 is enabled in the current Security state.

VMMeaning
0b0

EL1&0 stage 2 address translation disabled.

0b1

EL1&0 stage 2 address translation enabled.

When the value of this bit is 1, data cache invalidate instructions executed at EL1 perform a data cache clean and invalidate. For the invalidate by set/way instruction this behavior applies regardless of the value of the HCR_EL2.SWIO bit.

This bit is permitted to be cached in a TLB.

When ARMv8.1-VHE is implemented, and the value of HCR_EL2.{E2H, TGE} is {1, 1}, this field behaves as 0 for all purposes other than a direct read of the value of this bit.

This field resets to an architecturally UNKNOWN value.

Accessing the HCR_EL2

Accesses to this register use the following encodings:

MRS <Xt>, HCR_EL2

op0op1CRnCRmop2
0b110b1000b00010b00010b000
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && HCR_EL2.<NV2,NV> == '11' then
        return NVMem[0x078];
    elsif EL2Enabled() && HCR_EL2.NV == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    else
        UNDEFINED;
elsif PSTATE.EL == EL2 then
    return HCR_EL2;
elsif PSTATE.EL == EL3 then
    return HCR_EL2;
              

MSR HCR_EL2, <Xt>

op0op1CRnCRmop2
0b110b1000b00010b00010b000
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && HCR_EL2.<NV2,NV> == '11' then
        NVMem[0x078] = X[t];
    elsif EL2Enabled() && HCR_EL2.NV == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    else
        UNDEFINED;
elsif PSTATE.EL == EL2 then
    HCR_EL2 = X[t];
elsif PSTATE.EL == EL3 then
    HCR_EL2 = X[t];
              


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