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arm64: apple: Ask a hypervisor about IMPDEF registers only over HVC #910

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Merged
RyanTheTide merged 1 commit into from
Nov 5, 2026
Merged

arm64: apple: Ask a hypervisor about IMPDEF registers only over HVC #910

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33 changes: 19 additions & 14 deletions arch/arm64/kernel/cpufeature_impdef.c
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Original file line number Diff line number Diff line change
Expand Up @@ -70,6 +70,21 @@ static bool has_tso_fixed(const struct arm64_cpu_capabilities *entry, int scope)
}
#endif

/*
* Below EL2 a hypervisor traps IMPLEMENTATION DEFINED registers (KVM through
* HCR_EL2.TIDCP) and injects an UNDEF unless it emulates them, which it says
* through an Aurora vendor hypervisor feature. KVM guests call it through
* HVC. Anything else isn't a hypervisor to ask: aura's EL2 monitor, which
* enters the OS at EL1 on M4 machines with PSCI over SMC, does not trap these
* registers.
*/
static bool __maybe_unused apple_impdef_reg_usable(u32 feature)
{
return is_kernel_in_hyp_mode() ||
arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_HVC ||
kvm_arm_hyp_service_available(feature);
}

#ifdef CONFIG_ARM64_APPLE_X86_FLAGS
static bool has_apple_apflg(const struct arm64_cpu_capabilities *entry, int scope)
{
Expand All @@ -81,13 +96,8 @@ static bool has_apple_apflg(const struct arm64_cpu_capabilities *entry, int scop
!cpufeature_matches(read_sysreg(aidr_el1), entry))
return false;

/*
* Exception entry and return access ASPSR_EL1. Below EL2 a hypervisor
* traps that IMPDEF register (KVM through HCR_EL2.TIDCP) and would
* inject an UNDEF, so require it to say that it emulates ASPSR.
*/
if (!is_kernel_in_hyp_mode() &&
!kvm_arm_hyp_service_available(ARM_SMCCC_KVM_FUNC_AURORA_APPLE_ASPSR))
/* Exception entry and return access ASPSR_EL1. */
if (!apple_impdef_reg_usable(ARM_SMCCC_KVM_FUNC_AURORA_APPLE_ASPSR))
return false;

/*
Expand Down Expand Up @@ -127,13 +137,8 @@ static bool has_apple_afp(const struct arm64_cpu_capabilities *entry, int scope)
!cpufeature_matches(read_sysreg(aidr_el1), entry))
return false;

/*
* The kernel switches AFPCR_EL0 between threads. Below EL2 a hypervisor
* traps that IMPDEF register (KVM through HCR_EL2.TIDCP) and would
* inject an UNDEF, so require it to say that it emulates AFPCR.
*/
if (!is_kernel_in_hyp_mode() &&
!kvm_arm_hyp_service_available(ARM_SMCCC_KVM_FUNC_AURORA_APPLE_AFPCR))
/* The kernel switches AFPCR_EL0 between threads. */
if (!apple_impdef_reg_usable(ARM_SMCCC_KVM_FUNC_AURORA_APPLE_AFPCR))
return false;

val = read_sysreg(actlr_el1);
Expand Down