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KVM: arm64: pmu: Fix cycle counter truncation

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When a counter is disabled, its value is sampled before the event
is being disabled, and the value written back in the shadow register.

In that process, the value gets truncated to 32bit, which is adequate
for any counter but the cycle counter (defined as a 64bit counter).

This obviously results in a corrupted counter, and things like
"perf record -e cycles" not working at all when run in a guest...
A similar, but less critical bug exists in kvm_pmu_get_counter_value.

Make the truncation conditional on the counter not being the cycle
counter, which results in a minor code reorganisation.

Fixes: 80f393a23be6 ("KVM: arm/arm64: Support chained PMU counters")
Reviewed-by: Andrew Murray <andrew.murray@arm.com>
Reported-by: Julien Thierry <julien.thierry.kdev@gmail.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
This commit is contained in:
Marc Zyngier 2019-10-03 18:02:08 +01:00
parent da0c9ea146
commit f4e23cf947
1 changed files with 12 additions and 10 deletions
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22
virt/kvm/arm/pmu.c
View File

@ -146,8 +146,7 @@ u64 kvm_pmu_get_counter_value(struct kvm_vcpu *vcpu, u64 select_idx)
if (kvm_pmu_pmc_is_chained(pmc) &&
kvm_pmu_idx_is_high_counter(select_idx))
counter = upper_32_bits(counter);
else if (!kvm_pmu_idx_is_64bit(vcpu, select_idx))
else if (select_idx != ARMV8_PMU_CYCLE_IDX)
counter = lower_32_bits(counter);
return counter;
@ -193,7 +192,7 @@ static void kvm_pmu_release_perf_event(struct kvm_pmc *pmc)
*/
static void kvm_pmu_stop_counter(struct kvm_vcpu *vcpu, struct kvm_pmc *pmc)
{
u64 counter, reg;
u64 counter, reg, val;
pmc = kvm_pmu_get_canonical_pmc(pmc);
if (!pmc->perf_event)
@ -201,16 +200,19 @@ static void kvm_pmu_stop_counter(struct kvm_vcpu *vcpu, struct kvm_pmc *pmc)
counter = kvm_pmu_get_pair_counter_value(vcpu, pmc);
if (kvm_pmu_pmc_is_chained(pmc)) {
reg = PMEVCNTR0_EL0 + pmc->idx;
__vcpu_sys_reg(vcpu, reg) = lower_32_bits(counter);
__vcpu_sys_reg(vcpu, reg + 1) = upper_32_bits(counter);
if (pmc->idx == ARMV8_PMU_CYCLE_IDX) {
reg = PMCCNTR_EL0;
val = counter;
} else {
reg = (pmc->idx == ARMV8_PMU_CYCLE_IDX)
? PMCCNTR_EL0 : PMEVCNTR0_EL0 + pmc->idx;
__vcpu_sys_reg(vcpu, reg) = lower_32_bits(counter);
reg = PMEVCNTR0_EL0 + pmc->idx;
val = lower_32_bits(counter);
}
__vcpu_sys_reg(vcpu, reg) = val;
if (kvm_pmu_pmc_is_chained(pmc))
__vcpu_sys_reg(vcpu, reg + 1) = upper_32_bits(counter);
kvm_pmu_release_perf_event(pmc);
}