[PATCH v2 2/2] KVM: arm64: Check ID_AA64DFR0_EL1.PMUVer in pmu_visibility()

[Colton Lewis]

pmu_visibility() currently checks kvm_vcpu_has_pmu(), which only tests
whether the vCPU was initialized with KVM_ARM_VCPU_PMU_V3. If userspace
initializes a vCPU with KVM_ARM_VCPU_PMU_V3 and subsequently hides
FEAT_PMUv3 via ID_AA64DFR0_EL1.PMUVer, KVM continues to expose the PMU
system registers instead of emulating guest accesses as UNDEF.

Check ID_AA64DFR0_EL1.PMUVer directly via kvm_has_feat() in
pmu_visibility() so that PMU system registers are marked REG_HIDDEN
whenever FEAT_PMUv3 is not advertised in the ID registers.

Suggested-by: Oliver Upton <oupton at kernel.org>
Assisted-by: LLM
Signed-off-by: Colton Lewis <coltonlewis at google.com>
---
 arch/arm64/kvm/sys_regs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index e4ad9c171c7ca..46dd6e16de28e 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1029,7 +1029,7 @@ static unsigned int hidden_visibility(const struct kvm_vcpu *vcpu,
 static unsigned int pmu_visibility(const struct kvm_vcpu *vcpu,
 				   const struct sys_reg_desc *r)
 {
-	if (kvm_vcpu_has_pmu(vcpu))
+	if (kvm_has_feat(vcpu->kvm, ID_AA64DFR0_EL1, PMUVer, IMP))
 		return 0;
 
 	return REG_HIDDEN;
-- 
2.56.0.rc1.315.gc6ed9934b7-goog