[PATCH 1/1] KVM: arm64: PMU: Avoid inappropriate use of host's PMUVer

[Reiji Watanabe]

Avoid using the PMUVer of the host's PMU hardware (including
the sanitized value of the PMUVer) for vPMU control purposes,
except in a few cases, as the value of host's PMUVer may differ
from the value of ID_AA64DFR0_EL1.PMUVer for the guest.

The first case is when using the PMUVer as the limit value of
the ID_AA64DFR0_EL1.PMUVer for the guest. The second case is
when using the PMUVer to determine the valid range of events for
KVM_ARM_VCPU_PMU_V3_FILTER, as it has been allowing userspace to
specify events that are valid for the PMU hardware, regardless of
the value of the guest's ID_AA64DFR0_EL1.PMUVer. KVM will change
the valid range of the event that the guest can use based on the
value of the guest's ID_AA64DFR0_EL1.PMUVer though.

Signed-off-by: Reiji Watanabe <reijiw at google.com>
---
 arch/arm64/kvm/pmu-emul.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index 491ca7eb2a4c..2d52f44de4a1 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -35,12 +35,8 @@ static struct kvm_pmc *kvm_vcpu_idx_to_pmc(struct kvm_vcpu *vcpu, int cnt_idx)
 	return &vcpu->arch.pmu.pmc[cnt_idx];
 }
 
-static u32 kvm_pmu_event_mask(struct kvm *kvm)
+static u32 __kvm_pmu_event_mask(unsigned int pmuver)
 {
-	unsigned int pmuver;
-
-	pmuver = kvm->arch.arm_pmu->pmuver;
-
 	switch (pmuver) {
 	case ID_AA64DFR0_EL1_PMUVer_IMP:
 		return GENMASK(9, 0);
@@ -55,6 +51,11 @@ static u32 kvm_pmu_event_mask(struct kvm *kvm)
 	}
 }
 
+static u32 kvm_pmu_event_mask(struct kvm *kvm)
+{
+	return __kvm_pmu_event_mask(kvm->arch.dfr0_pmuver.imp);
+}
+
 /**
  * kvm_pmc_is_64bit - determine if counter is 64bit
  * @pmc: counter context
@@ -735,7 +736,7 @@ u64 kvm_pmu_get_pmceid(struct kvm_vcpu *vcpu, bool pmceid1)
 		 * Don't advertise STALL_SLOT, as PMMIR_EL0 is handled
 		 * as RAZ
 		 */
-		if (vcpu->kvm->arch.arm_pmu->pmuver >= ID_AA64DFR0_EL1_PMUVer_V3P4)
+		if (vcpu->kvm->arch.dfr0_pmuver.imp >= ID_AA64DFR0_EL1_PMUVer_V3P4)
 			val &= ~BIT_ULL(ARMV8_PMUV3_PERFCTR_STALL_SLOT - 32);
 		base = 32;
 	}
@@ -932,11 +933,17 @@ int kvm_arm_pmu_v3_set_attr(struct kvm_vcpu *vcpu, struct kvm_device_attr *attr)
 		return 0;
 	}
 	case KVM_ARM_VCPU_PMU_V3_FILTER: {
+		u8 pmuver = kvm_arm_pmu_get_pmuver_limit();
 		struct kvm_pmu_event_filter __user *uaddr;
 		struct kvm_pmu_event_filter filter;
 		int nr_events;
 
-		nr_events = kvm_pmu_event_mask(kvm) + 1;
+		/*
+		 * Allow userspace to specify an event filter for the entire
+		 * event range supported by PMUVer of the hardware, rather
+		 * than the guest's PMUVer for KVM backward compatibility.
+		 */
+		nr_events = __kvm_pmu_event_mask(pmuver) + 1;
 
 		uaddr = (struct kvm_pmu_event_filter __user *)(long)attr->addr;
 
-- 
2.41.0.162.gfafddb0af9-goog