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TCR_EL3, Translation Control Register (EL3)

The TCR_EL3 characteristics are:

Purpose

The control register for stage 1 of the EL3 translation regime.

Configuration

RW fields in this register reset to architecturally UNKNOWN values.

Attributes

TCR_EL3 is a 64-bit register.

Field descriptions

The TCR_EL3 bit assignments are:

6362616059585756555453525150494847464544434241403938373635343332
RES0
RES1TCMATBIDHWU62HWU61HWU60HWU59HPDRES1HDHATBIRES0PSTG0SH0ORGN0IRGN0RES0T0SZ
313029282726252423222120191817161514131211109876543210

Any of the bits in TCR_EL3 are permitted to be cached in a TLB.

Bits [63:32]

Reserved, RES0.

Bit [31]

Reserved, RES1.

TCMA, bit [30]

When ARMv8.5-MemTag is implemented:

Controls the generation of Unchecked accesses at EL3 when address [59:56] = 0b0000.

TCMAMeaning
0b0

This control has no effect on the generation of Unchecked accesses.

0b1

All accesses are Unchecked.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

TBID, bit [29]

When ARMv8.3-PAuth is implemented:

Controls the use of the top byte of instruction addresses for address matching.

TBIDMeaning
0b0

TCR_EL3.TBI applies to Instruction and Data accesses.

0b1

TCR_EL3.TBI applies to Data accesses only.

This affects addresses where the address would be translated by tables pointed to by TTBR0_EL3.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

HWU62, bit [28]

When ARMv8.2-TTPBHA is implemented:

Hardware Use. Indicates IMPLEMENTATION DEFINED hardware use of bit[62] of the stage 1 translation table Block or Page entry.

HWU62Meaning
0b0

Bit[62] of each stage 1 translation table Block or Page entry cannot be used by hardware for an IMPLEMENTATION DEFINED purpose.

0b1

Bit[62] of each stage 1 translation table Block or Page entry can be used by hardware for an IMPLEMENTATION DEFINED purpose if the value of TCR_EL3.HPD is 1.

The Effective value of this field is 0 if the value of TCR_EL3.HPD is 0.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

HWU61, bit [27]

When ARMv8.2-TTPBHA is implemented:

Hardware Use. Indicates IMPLEMENTATION DEFINED hardware use of bit[61] of the stage 1 translation table Block or Page entry.

HWU61Meaning
0b0

Bit[61] of each stage 1 translation table Block or Page entry cannot be used by hardware for an IMPLEMENTATION DEFINED purpose.

0b1

Bit[61] of each stage 1 translation table Block or Page entry can be used by hardware for an IMPLEMENTATION DEFINED purpose if the value of TCR_EL3.HPD is 1.

The Effective value of this field is 0 if the value of TCR_EL3.HPD is 0.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

HWU60, bit [26]

When ARMv8.2-TTPBHA is implemented:

Hardware Use. Indicates IMPLEMENTATION DEFINED hardware use of bit[60] of the stage 1 translation table Block or Page entry.

HWU60Meaning
0b0

Bit[60] of each stage 1 translation table Block or Page entry cannot be used by hardware for an IMPLEMENTATION DEFINED purpose.

0b1

Bit[60] of each stage 1 translation table Block or Page entry can be used by hardware for an IMPLEMENTATION DEFINED purpose if the value of TCR_EL3.HPD is 1.

The Effective value of this field is 0 if the value of TCR_EL3.HPD is 0.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

HWU59, bit [25]

When ARMv8.2-TTPBHA is implemented:

Hardware Use. Indicates IMPLEMENTATION DEFINED hardware use of bit[59] of the stage 1 translation table Block or Page entry.

HWU59Meaning
0b0

Bit[59] of each stage 1 translation table Block or Page entry cannot be used by hardware for an IMPLEMENTATION DEFINED purpose.

0b1

Bit[59] of each stage 1 translation table Block or Page entry can be used by hardware for an IMPLEMENTATION DEFINED purpose if the value of TCR_EL3.HPD is 1.

The Effective value of this field is 0 if the value of TCR_EL3.HPD is 0.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

HPD, bit [24]

When ARMv8.1-HPD is implemented:

Hierarchical Permission Disables. This affects the hierarchical control bits, APTable, PXNTable, and UXNTable, except NSTable, in the translation tables pointed to by TTBR0_EL3.

HPDMeaning
0b0

Hierarchical permissions are enabled.

0b1

Hierarchical permissions are disabled.

Note

In this case bit[61] (APTable[0]) and bit[59] (PXNTable) of the next level descriptor attributes are required to be ignored by the PE, and are no longer reserved, allowing them to be used by software.

When disabled, the permissions are treated as if the bits are zero.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

Bit [23]

Reserved, RES1.

HD, bit [22]

When ARMv8.1-TTHM is implemented:

Hardware management of dirty state in stage 1 translations from EL3.

HDMeaning
0b0

Stage 1 hardware management of dirty state disabled.

0b1

Stage 1 hardware management of dirty state enabled, only if the HA bit is also set to 1.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

HA, bit [21]

When ARMv8.1-TTHM is implemented:

Hardware Access flag update in stage 1 translations from EL3.

HAMeaning
0b0

Stage 1 Access flag update disabled.

0b1

Stage 1 Access flag update enabled.

This field resets to an architecturally UNKNOWN value.


Otherwise:

Reserved, RES0.

TBI, bit [20]

Top Byte Ignored. Indicates whether the top byte of an address is used for address match for the TTBR0_EL3 region, or ignored and used for tagged addresses.

TBIMeaning
0b0

Top Byte used in the address calculation.

0b1

Top Byte ignored in the address calculation.

This affects addresses generated in EL3 using AArch64 where the address would be translated by tables pointed to by TTBR0_EL3. It has an effect whether the EL3 translation regime is enabled or not.

If ARMv8.3-PAuth is implemented and TCR_EL3.TBID is 1, then this field only applies to Data accesses.

Otherwise, if the value of TBI is 1, then bits[63:56] of that target address are also set to 0 before the address is stored in the PC, in the following cases:

  • A branch or procedure return within EL3.
  • A exception taken to EL3.
  • An exception return to EL3.

For more information, see 'Address tagging in AArch64 state' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile.

Note

This control detrmines the scope of address tagging. It never causes an exception to be generated.

This field resets to an architecturally UNKNOWN value.

Bit [19]

Reserved, RES0.

PS, bits [18:16]

Physical Address Size.

PSMeaning
0b000

32 bits, 4GB.

0b001

36 bits, 64GB.

0b010

40 bits, 1TB.

0b011

42 bits, 4TB.

0b100

44 bits, 16TB.

0b101

48 bits, 256TB.

0b110

52 bits, 4PB.

Other values are reserved.

The reserved values behave in the same way as the 0b101 or 0b110 encoding, but software must not rely on this property as the behavior of the reserved values might change in a future revision of the architecture.

The value 0b110 is permitted only if ARMv8.2-LPA is implemented and the translation granule size is 64KB.

In an implementation that supports 52-bit PAs, if the value of this field is not 0b110 or a value treated as 0b110, then bits[51:48] of every translation table base address for the stage of translation controlled by TCR_EL3 are 0b0000.

This field resets to an architecturally UNKNOWN value.

TG0, bits [15:14]

Granule size for the TTBR0_EL3.

TG0Meaning
0b00

4KB.

0b01

64KB.

0b10

16KB.

Other values are reserved.

If the value is programmed to either a reserved value, or a size that has not been implemented, then the hardware will treat the field as if it has been programmed to an IMPLEMENTATION DEFINED choice of the sizes that has been implemented for all purposes other than the value read back from this register.

It is IMPLEMENTATION DEFINED whether the value read back is the value programmed or the value that corresponds to the size chosen.

This field resets to an architecturally UNKNOWN value.

SH0, bits [13:12]

Shareability attribute for memory associated with translation table walks using TTBR0_EL3.

SH0Meaning
0b00

Non-shareable.

0b10

Outer Shareable.

0b11

Inner Shareable.

Other values are reserved. The effect of programming this field to a Reserved value is that behavior is CONSTRAINED UNPREDICTABLE, as described in 'Reserved values in AArch64 System registers and translation table entries' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile, section K1.2.2.

This field resets to an architecturally UNKNOWN value.

ORGN0, bits [11:10]

Outer cacheability attribute for memory associated with translation table walks using TTBR0_EL3.

ORGN0Meaning
0b00

Normal memory, Outer Non-cacheable.

0b01

Normal memory, Outer Write-Back Read-Allocate Write-Allocate Cacheable.

0b10

Normal memory, Outer Write-Through Read-Allocate No Write-Allocate Cacheable.

0b11

Normal memory, Outer Write-Back Read-Allocate No Write-Allocate Cacheable.

This field resets to an architecturally UNKNOWN value.

IRGN0, bits [9:8]

Inner cacheability attribute for memory associated with translation table walks using TTBR0_EL3.

IRGN0Meaning
0b00

Normal memory, Inner Non-cacheable.

0b01

Normal memory, Inner Write-Back Read-Allocate Write-Allocate Cacheable.

0b10

Normal memory, Inner Write-Through Read-Allocate No Write-Allocate Cacheable.

0b11

Normal memory, Inner Write-Back Read-Allocate No Write-Allocate Cacheable.

This field resets to an architecturally UNKNOWN value.

Bits [7:6]

Reserved, RES0.

T0SZ, bits [5:0]

The size offset of the memory region addressed by TTBR0_EL3. The region size is 2(64-T0SZ) bytes.

The maximum and minimum possible values for T0SZ depend on the level of translation table and the memory translation granule size, as described in the AArch64 Virtual Memory System Architecture chapter.

This field resets to an architecturally UNKNOWN value.

Accessing the TCR_EL3

Accesses to this register use the following encodings:

MRS <Xt>, TCR_EL3

op0op1CRnCRmop2
0b110b1100b00100b00000b010
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    UNDEFINED;
elsif PSTATE.EL == EL2 then
    UNDEFINED;
elsif PSTATE.EL == EL3 then
    return TCR_EL3;
              

MSR TCR_EL3, <Xt>

op0op1CRnCRmop2
0b110b1100b00100b00000b010
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    UNDEFINED;
elsif PSTATE.EL == EL2 then
    UNDEFINED;
elsif PSTATE.EL == EL3 then
    TCR_EL3 = X[t];
              


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