[PATCH] KVM: arm64: Check ID_AA64DFR0_EL1.PMUVer in reset_pmevtyper()

[Colton Lewis]

When userspace initializes a vCPU with KVM_ARM_VCPU_PMU_V3 but sets
ID_AA64DFR0_EL1.PMUVer to NI (0) or IMP_DEF (0xf, which is sanitized to
NI), resetting the vCPU invokes reset_pmevtyper(). Because
reset_pmevtyper() only checks kvm_vcpu_has_pmu(), it proceeds to call
kvm_pmu_evtyper_mask(), which reads PMUVer == 0 from ID_AA64DFR0_EL1 and
triggers a WARN_ONCE("Unknown PMU version 0") in __kvm_pmu_event_mask().

Check ID_AA64DFR0_EL1.PMUVer directly in reset_pmevtyper() via
kvm_has_feat() instead of kvm_vcpu_has_pmu() so that PMEVTYPER<n>_EL0
resets to 0 without querying the event mask when PMUv3 is not exposed to
the guest.

Fixes: bc512d6a9b92 ("KVM: arm64: Make PMEVTYPER<n>_EL0.NSH RES0 if EL2 isn't advertised")
Suggested-by: Oliver Upton <oupton@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Assisted-by: LLM
Signed-off-by: Colton Lewis <coltonlewis@xxxxxxxxxx>
---
 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 a2f4e769a4282..0bb3c2f10a22c 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1060,7 +1060,7 @@ static u64 reset_pmevcntr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
 static u64 reset_pmevtyper(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
 {
 	/* This thing will UNDEF, who cares about the reset value? */
-	if (!kvm_vcpu_has_pmu(vcpu))
+	if (!kvm_has_feat(vcpu->kvm, ID_AA64DFR0_EL1, PMUVer, IMP))
 		return 0;
 
 	reset_unknown(vcpu, r);
-- 
2.56.0.rc1.315.gc6ed9934b7-goog