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FAR_EL3, Fault Address Register (EL3)

The FAR_EL3 characteristics are:

Purpose

Holds the faulting Virtual Address for all synchronous Instruction or Data Abort and PC alignment fault exceptions that are taken to EL3.

Configuration

RW fields in this register reset to architecturally UNKNOWN values.

Attributes

FAR_EL3 is a 64-bit register.

Field descriptions

The FAR_EL3 bit assignments are:

6362616059585756555453525150494847464544434241403938373635343332
Faulting Virtual Address for synchronous exceptions taken to EL3
Faulting Virtual Address for synchronous exceptions taken to EL3
313029282726252423222120191817161514131211109876543210

Bits [63:0]

Faulting Virtual Address for synchronous exceptions taken to EL3. Exceptions that set the FAR_EL3 are Instruction Aborts (EC 0x20 or 0x21), Data Aborts (EC 0x24 or 0x25), and PC alignment faults (EC 0x22). ESR_EL3.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_EL3 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_EL3.FnV is 0, and the FAR_EL3 is UNKNOWN if ESR_EL3.FnV is 1.

For all other exceptions taken to EL3, the FAR_EL3 is UNKNOWN.

If a memory fault that sets FAR_EL3 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_EL3 is taken from an Exception Level 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.

Execution at EL2, EL1 or EL0 makes FAR_EL3 become UNKNOWN.

Note

The address held in this register is an address accessed by the instruction fetch or data access that caused the exception that actually gave rise to the instruction or data abort. It is the lowest 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_EL3 is made UNKNOWN on an exception return from EL3.

This field resets to an architecturally UNKNOWN value.

Accessing the FAR_EL3

Accesses to this register use the following encodings:

MRS <Xt>, FAR_EL3

op0op1CRnCRmop2
0b110b1100b01100b00000b000
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    UNDEFINED;
elsif PSTATE.EL == EL2 then
    UNDEFINED;
elsif PSTATE.EL == EL3 then
    return FAR_EL3;
              

MSR FAR_EL3, <Xt>

op0op1CRnCRmop2
0b110b1100b01100b00000b000
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    UNDEFINED;
elsif PSTATE.EL == EL2 then
    UNDEFINED;
elsif PSTATE.EL == EL3 then
    FAR_EL3 = X[t];
              


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