Hypervisor Activity Monitors Fine-Grained Read Trap Register
Provides controls for traps of MRS reads of Activity Monitors System registers.
This register is present only when FEAT_AMUv1 is implemented, FEAT_FGT is implemented, and FEAT_AA64 is implemented. Otherwise, direct accesses to HAFGRTR_EL2 are UNDEFINED.
If EL2 is not implemented, this register is RES0 from EL3.
HAFGRTR_EL2 is a 64-bit register.
Reserved, RES0.
Trap MRS reads of AMEVTYPER1<x>_EL0 at EL1 and EL0 using AArch64 and MRC reads of AMEVTYPER1<x> at EL0 using AArch32 when EL1 is using AArch64 to EL2.
| AMEVTYPER1<x>_EL0 | Meaning |
|---|---|
| 0b0 |
MRS reads of AMEVTYPER1<x>_EL0 at EL1 and EL0 using AArch64 and MRC reads of AMEVTYPER1<x> at EL0 using AArch32 are not trapped by this mechanism. |
| 0b1 | If EL2 is implemented and enabled in the current Security state, the Effective value of HCR_EL2.{E2H, TGE} is not {1, 1}, EL1 is using AArch64, and either EL3 is not implemented or SCR_EL3.FGTEn == 1, then, unless the read generates a higher priority exception:
|
The reset behavior of this field is:
Accessing this field has the following behavior:
Trap MRS reads of AMEVCNTR1<x>_EL0 at EL1 and EL0 using AArch64 and MRC reads of AMEVCNTR1<x> at EL0 using AArch32 when EL1 is using AArch64 to EL2.
| AMEVCNTR1<x>_EL0 | Meaning |
|---|---|
| 0b0 |
MRS reads of AMEVCNTR1<x>_EL0 at EL1 and EL0 using AArch64 and MRC reads of AMEVCNTR1<x> at EL0 using AArch32 are not trapped by this mechanism. |
| 0b1 | If EL2 is implemented and enabled in the current Security state, the Effective value of HCR_EL2.{E2H, TGE} is not {1, 1}, EL1 is using AArch64, and either EL3 is not implemented or SCR_EL3.FGTEn == 1, then, unless the read generates a higher priority exception:
|
The reset behavior of this field is:
Accessing this field has the following behavior:
Trap MRS reads and MRC reads of multiple System registers.
Enables a trap to EL2 the following operations:
| AMCNTEN<x> | Meaning |
|---|---|
| 0b0 |
The operations listed above are not trapped by this mechanism. |
| 0b1 | If EL2 is implemented and enabled in the current Security state, the Effective value of HCR_EL2.{E2H, TGE} is not {1, 1}, EL1 is using AArch64, and either EL3 is not implemented or SCR_EL3.FGTEn == 1, then, unless the read generates a higher priority exception:
|
The reset behavior of this field is:
Reserved, RES0.
Trap MRS reads of AMEVCNTR0<x>_EL0 at EL1 and EL0 using AArch64 and MRC reads of AMEVCNTR0<x> at EL0 using AArch32 when EL1 is using AArch64 to EL2.
| AMEVCNTR0<x>_EL0 | Meaning |
|---|---|
| 0b0 |
MRS reads of AMEVCNTR0<x>_EL0 at EL1 and EL0 using AArch64 and MRC reads of AMEVCNTR0<x> at EL0 using AArch32 are not trapped by this mechanism. |
| 0b1 | If EL2 is implemented and enabled in the current Security state, the Effective value of HCR_EL2.{E2H, TGE} is not {1, 1}, EL1 is using AArch64, and either EL3 is not implemented or SCR_EL3.FGTEn == 1, then, unless the read generates a higher priority exception:
|
The reset behavior of this field is:
When x >= 4, access to this field is RES0 .
Accesses to this register use the following encodings in the System register encoding space:
MRS <Xt>, HAFGRTR_EL2
(op0 = 0b11, op1 = 0b100, CRn = 0b0011, CRm = 0b0001, op2 = 0b110)
if !(IsFeatureImplemented(FEAT_AMUv1) && IsFeatureImplemented(FEAT_FGT) && IsFeatureImplemented(FEAT_AA64)) then Undefined(); elsif HaveEL(EL3) && PSTATE.EL == EL2 && EL3SDDUndefPriority() && SCR_EL3().FGTEn == '0' then Undefined(); elsif PSTATE.EL == EL0 then Undefined(); elsif PSTATE.EL == EL1 then if EffectiveHCR_EL2_NVx() IN {'1x1'} then X{64}(t) = NVMem(0x1E8); elsif EffectiveHCR_EL2_NVx() IN {'xx1'} then AArch64_SystemAccessTrap(EL2, 0x18); else Undefined(); end; elsif PSTATE.EL == EL2 then if HaveEL(EL3) && SCR_EL3().FGTEn == '0' then if EL3SDDUndef() then Undefined(); else AArch64_SystemAccessTrap(EL3, 0x18); end; else X{64}(t) = HAFGRTR_EL2(); end; elsif PSTATE.EL == EL3 then X{64}(t) = HAFGRTR_EL2(); end;
MSR HAFGRTR_EL2, <Xt>
(op0 = 0b11, op1 = 0b100, CRn = 0b0011, CRm = 0b0001, op2 = 0b110)
if !(IsFeatureImplemented(FEAT_AMUv1) && IsFeatureImplemented(FEAT_FGT) && IsFeatureImplemented(FEAT_AA64)) then Undefined(); elsif HaveEL(EL3) && PSTATE.EL == EL2 && EL3SDDUndefPriority() && SCR_EL3().FGTEn == '0' then Undefined(); elsif PSTATE.EL == EL0 then Undefined(); elsif PSTATE.EL == EL1 then if EffectiveHCR_EL2_NVx() IN {'1x1'} then NVMem(0x1E8) = X{64}(t); elsif EffectiveHCR_EL2_NVx() IN {'xx1'} then AArch64_SystemAccessTrap(EL2, 0x18); else Undefined(); end; elsif PSTATE.EL == EL2 then if HaveEL(EL3) && SCR_EL3().FGTEn == '0' then if EL3SDDUndef() then Undefined(); else AArch64_SystemAccessTrap(EL3, 0x18); end; else HAFGRTR_EL2() = X{64}(t); end; elsif PSTATE.EL == EL3 then HAFGRTR_EL2() = X{64}(t); end;
Version 2026.06 — Copyright © 2010-2026 Arm Limited or its affiliates.
This site is provided as a community resource and is NOT affiliated with nor endorsed by Arm Limited.