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CONTEXTIDR_EL2, Context ID Register (EL2)

The CONTEXTIDR_EL2 characteristics are:

Purpose

Identifies the current Process Identifier for EL2.

The value of the whole of this register is called the Context ID and is used by:

  • The debug logic, for Linked and Unlinked Context ID matching.
  • The trace logic, to identify the current process.

The significance of this register is for debug and trace use only.

Configuration

This register is present only when FEAT_VHE is implemented or FEAT_Debugv8p2 is implemented. Otherwise, direct accesses to CONTEXTIDR_EL2 are UNDEFINED.

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.

Attributes

CONTEXTIDR_EL2 is a 64-bit register.

Field descriptions

The CONTEXTIDR_EL2 bit assignments are:

6362616059585756555453525150494847464544434241403938373635343332
RES0
PROCID
313029282726252423222120191817161514131211109876543210

Bits [63:32]

Reserved, RES0.

PROCID, bits [31:0]

Process Identifier. This field must be programmed with a unique value that identifies the current process.

On a Warm reset, this field resets to an architecturally UNKNOWN value.

Accessing the CONTEXTIDR_EL2

When HCR_EL2.E2H is 1, without explicit synchronization, access from EL2 using the mnemonic CONTEXTIDR_EL2 or CONTEXTIDR_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>, CONTEXTIDR_EL2

op0op1CRnCRmop2
0b110b1000b11010b00000b001
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && HCR_EL2.NV == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    else
        UNDEFINED;
elsif PSTATE.EL == EL2 then
    return CONTEXTIDR_EL2;
elsif PSTATE.EL == EL3 then
    return CONTEXTIDR_EL2;
              

MSR CONTEXTIDR_EL2, <Xt>

op0op1CRnCRmop2
0b110b1000b11010b00000b001
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && HCR_EL2.NV == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    else
        UNDEFINED;
elsif PSTATE.EL == EL2 then
    CONTEXTIDR_EL2 = X[t];
elsif PSTATE.EL == EL3 then
    CONTEXTIDR_EL2 = X[t];
              

MRS <Xt>, CONTEXTIDR_EL1

op0op1CRnCRmop2
0b110b0000b11010b00000b001
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && HCR_EL2.TRVM == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    elsif EL2Enabled() && (!HaveEL(EL3) || SCR_EL3.FGTEn == '1') && HFGRTR_EL2.CONTEXTIDR_EL1 == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    elsif EL2Enabled() && HCR_EL2.<NV2,NV1,NV> == '111' then
        return NVMem[0x108];
    else
        return CONTEXTIDR_EL1;
elsif PSTATE.EL == EL2 then
    if HCR_EL2.E2H == '1' then
        return CONTEXTIDR_EL2;
    else
        return CONTEXTIDR_EL1;
elsif PSTATE.EL == EL3 then
    return CONTEXTIDR_EL1;
              

MSR CONTEXTIDR_EL1, <Xt>

op0op1CRnCRmop2
0b110b0000b11010b00000b001
if PSTATE.EL == EL0 then
    UNDEFINED;
elsif PSTATE.EL == EL1 then
    if EL2Enabled() && HCR_EL2.TVM == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    elsif EL2Enabled() && (!HaveEL(EL3) || SCR_EL3.FGTEn == '1') && HFGWTR_EL2.CONTEXTIDR_EL1 == '1' then
        AArch64.SystemAccessTrap(EL2, 0x18);
    elsif EL2Enabled() && HCR_EL2.<NV2,NV1,NV> == '111' then
        NVMem[0x108] = X[t];
    else
        CONTEXTIDR_EL1 = X[t];
elsif PSTATE.EL == EL2 then
    if HCR_EL2.E2H == '1' then
        CONTEXTIDR_EL2 = X[t];
    else
        CONTEXTIDR_EL1 = X[t];
elsif PSTATE.EL == EL3 then
    CONTEXTIDR_EL1 = X[t];