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FAR_EL2, Fault Address Register (EL2)

The FAR_EL2 characteristics are:

Purpose

Holds the faulting Virtual Address for all synchronous Instruction or Data Abort, PC alignment fault and Watchpoint exceptions that are taken to EL2.

Configuration

AArch64 System register FAR_EL2 bits [31:0] are architecturally mapped to AArch32 System register HDFAR[31:0] .

AArch64 System register FAR_EL2 bits [63:32] are architecturally mapped to AArch32 System register HIFAR[31:0] .

AArch64 System register FAR_EL2 bits [31:0] are architecturally mapped to AArch32 System register DFAR[31:0] (S) when HaveEL(EL2).

AArch64 System register FAR_EL2 bits [63:32] are architecturally mapped to AArch32 System register IFAR[31:0] (S) when HaveEL(EL2).

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

FAR_EL2 is a 64-bit register.

Field descriptions

The FAR_EL2 bit assignments are:

6362616059585756555453525150494847464544434241403938373635343332
Faulting Virtual Address for synchronous exceptions taken to EL2
Faulting Virtual Address for synchronous exceptions taken to EL2
313029282726252423222120191817161514131211109876543210

Bits [63:0]

Faulting Virtual Address for synchronous exceptions taken to EL2. Exceptions that set the FAR_EL2 are Instruction Aborts (EC 0x20 or 0x21), Data Aborts (EC 0x24 or 0x25), PC alignment faults (EC 0x22), and Watchpoints (EC 0x34 or 0x35). ESR_EL2.EC holds the EC value for the exception.

For a synchronous External abort, if the VA that generated the abort was from an address range for which TCR_ELx.TBI{<0|1>} == 1 for the translation regime in use when the abort was generated, then the top eight bits of FAR_EL2 are UNKNOWN.

For a synchronous External abort other than a synchronous External abort on a translation table walk, this field is valid only if ESR_EL2.FnV is 0, and the FAR_EL2 is UNKNOWN if ESR_EL2.FnV is 1.

For all other exceptions taken to EL2, the FAR_EL2 is UNKNOWN.

If a memory fault that sets FAR_EL2 is generated from a data cache maintenance or other DC instruction, this field holds the address specified in the register argument of the instruction.

If the exception that updates FAR_EL2 is taken from an Exception level that is using AArch32, the top 32 bits are all zero, unless both of the following apply, in which case the top 32 bits of FAR_ELx are 0x00000001:

  • The faulting address was generated by a load or store instruction that sequentially incremented from address 0xFFFFFFFF. Such a load or store instruction is CONSTRAINED UNPREDICTABLE. See 'Out of range VA' in Appendix K1 Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile.
  • The implementation treats such incrementing as setting bit[32] of the virtual address to 1.

For a Data Abort or Watchpoint exception, if address tagging is enabled for the address accessed by the data access that caused the exception, then this field includes the tag. For more information about address tagging, see 'Address tagging in AArch64 state' in the Arm® Architecture Reference Manual, Armv8, for Armv8-A architecture profile.

Note

The address held in this field is an address accessed by the instruction fetch or data access that caused the exception that gave rise to the instruction or data abort. It is the lower address that gave rise to the fault. Where different faults from different addresses arise from the same instruction, such as for an instruction that loads or stores a mis-aligned address that crosses a page boundary, the architecture does not prioritize between those different faults.

FAR_EL2 is made UNKNOWN on an exception return from EL2.

This field resets to an architecturally UNKNOWN value.

Accessing the FAR_EL2

When HCR_EL2.E2H is 1, without explicit synchronization, access from EL2 using the mnemonic FAR_EL2 or FAR_EL1 are not guaranteed to be ordered with respect to accesses using the other mnemonic.

Accesses to this register use the following encodings:

MRS <Xt>, FAR_EL2

op0CRnop1op2CRm
0b110b01100b1000b0000b0000
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && HCR_EL2.<NV2,NV> == '11' then
        return FAR_EL1;
    elsif EL2Enabled() && HCR_EL2.NV == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    else
        UNDEFINED;
elsif PSTATE.EL == EL2 then
    return FAR_EL2;
elsif PSTATE.EL == EL3 then
    return FAR_EL2;
              

MSR FAR_EL2, <Xt>

op0CRnop1op2CRm
0b110b01100b1000b0000b0000
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && HCR_EL2.<NV2,NV> == '11' then
        FAR_EL1 = X[t];
    elsif EL2Enabled() && HCR_EL2.NV == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    else
        UNDEFINED;
elsif PSTATE.EL == EL2 then
    FAR_EL2 = X[t];
elsif PSTATE.EL == EL3 then
    FAR_EL2 = X[t];
              

MRS <Xt>, FAR_EL1

op0CRnop1op2CRm
0b110b01100b0000b0000b0000
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TRVM == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.<NV2,NV1,NV> == '111' then
        return NVMem[0x220];
    else
        return FAR_EL1;
elsif PSTATE.EL == EL2 then
    if HCR_EL2.E2H == '1' then
        return FAR_EL2;
    else
        return FAR_EL1;
elsif PSTATE.EL == EL3 then
    return FAR_EL1;
              

MSR FAR_EL1, <Xt>

op0CRnop1op2CRm
0b110b01100b0000b0000b0000
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.TVM == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    elsif EL2Enabled() && !ELUsingAArch32(EL2) && HCR_EL2.<NV2,NV1,NV> == '111' then
        NVMem[0x220] = X[t];
    else
        FAR_EL1 = X[t];
elsif PSTATE.EL == EL2 then
    if HCR_EL2.E2H == '1' then
        FAR_EL2 = X[t];
    else
        FAR_EL1 = X[t];
elsif PSTATE.EL == EL3 then
    FAR_EL1 = X[t];
              


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