[PATCH v2 1/2] KVM: arm64: Handle ID_AA64DFR0_EL1.PMUVer == NI in __kvm_pmu_event_mask()

[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() and calls
kvm_pmu_evtyper_mask(). Because __kvm_pmu_event_mask() does not handle
ID_AA64DFR0_EL1_PMUVer_NI, it triggers a WARN_ONCE("Unknown PMU version
0").

Explicitly handle ID_AA64DFR0_EL1_PMUVer_NI in __kvm_pmu_event_mask() by
returning an event mask of 0, and drop the redundant kvm_vcpu_has_pmu()
check in reset_pmevtyper().

Fixes: bc512d6a9b92 ("KVM: arm64: Make PMEVTYPER<n>_EL0.NSH RES0 if EL2 isn't advertised")
Suggested-by: Oliver Upton <oupton@xxxxxxxxxx>
Assisted-by: LLM
Signed-off-by: Colton Lewis <coltonlewis@xxxxxxxxxx>
---
 arch/arm64/kvm/pmu-emul.c | 5 ++++-
 arch/arm64/kvm/sys_regs.c | 4 ----
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index 5b1af7e2176fa..e2b28dbc0451b 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -50,8 +50,11 @@ static u32 __kvm_pmu_event_mask(unsigned int pmuver)
 	case ID_AA64DFR0_EL1_PMUVer_V3P5:
 	case ID_AA64DFR0_EL1_PMUVer_V3P7:
 		return GENMASK(15, 0);
-	default:		/* Shouldn't be here, just for sanity */
+	default:
+		/* Shouldn't be here, just for sanity */
 		WARN_ONCE(1, "Unknown PMU version %d\n", pmuver);
+		fallthrough;
+	case ID_AA64DFR0_EL1_PMUVer_NI:
 		return 0;
 	}
 }
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index a2f4e769a4282..e4ad9c171c7ca 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1059,10 +1059,6 @@ 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))
-		return 0;
-
 	reset_unknown(vcpu, r);
 	__vcpu_rmw_sys_reg(vcpu, r->reg, &=, kvm_pmu_evtyper_mask(vcpu->kvm));
 
-- 
2.56.0.rc1.315.gc6ed9934b7-goog