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ACTLR_EL2, Auxiliary Control Register (EL2)

The ACTLR_EL2 characteristics are:

Purpose

Provides IMPLEMENTATION DEFINED configuration and control options for EL2.

Note

Arm recommends the contents of this register are updated to apply to EL0 when HCR_EL2.{E2H, TGE} is {1, 1}, gaining configuration and control fields from the ACTLR_EL1. This avoids the need for software to manage the contents of these register when switching between a Guest OS and a Host OS.

Configuration

AArch64 System register ACTLR_EL2 bits [31:0] are architecturally mapped to AArch32 System register HACTLR[31:0] .

AArch64 System register ACTLR_EL2 bits [63:32] are architecturally mapped to AArch32 System register HACTLR2[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.

Attributes

ACTLR_EL2 is a 64-bit register.

Field descriptions

The ACTLR_EL2 bit assignments are:

6362616059585756555453525150494847464544434241403938373635343332
IMPLEMENTATION DEFINED
IMPLEMENTATION DEFINED
313029282726252423222120191817161514131211109876543210

IMPLEMENTATION DEFINED, bits [63:0]

IMPLEMENTATION DEFINED.

This field resets to an architecturally UNKNOWN value.

Accessing the ACTLR_EL2

Accesses to this register use the following encodings:

MRS <Xt>, ACTLR_EL2

op0op1CRnCRmop2
0b110b1000b00010b00000b001
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 ACTLR_EL2;
elsif PSTATE.EL == EL3 then
    return ACTLR_EL2;
              

MSR ACTLR_EL2, <Xt>

op0op1CRnCRmop2
0b110b1000b00010b00000b001
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
    ACTLR_EL2 = X[t];
elsif PSTATE.EL == EL3 then
    ACTLR_EL2 = X[t];
              


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