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

Reiji Watanabe
2023-06-10T19:45:24Z

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@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