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KVM: x86/pmu: Fix type length error when reading pmu->fixed_ctr_ctrl

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Use a u64 instead of a u8 when taking a snapshot of pmu->fixed_ctr_ctrl
when reprogramming fixed counters, as truncating the value results in KVM
thinking fixed counter 2 is already disabled (the bug also affects fixed
counters 3+, but KVM doesn't yet support those).  As a result, if the
guest disables fixed counter 2, KVM will get a false negative and fail to
reprogram/disable emulation of the counter, which can leads to incorrect
counts and spurious PMIs in the guest.

Fixes: 76d287b234 ("KVM: x86/pmu: Drop "u8 ctrl, int idx" for reprogram_fixed_counter()")
Cc: stable@vger.kernel.org
Signed-off-by: Mingwei Zhang <mizhang@google.com>
Link: https://lore.kernel.org/r/20240123221220.3911317-1-mizhang@google.com
[sean: rewrite changelog to call out the effects of the bug]
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Mingwei Zhang 2024-01-23 22:12:20 +00:00 committed by Sean Christopherson
parent 6231c9e1a9
commit 05519c86d6
1 changed files with 1 additions and 1 deletions
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2
arch/x86/kvm/vmx/pmu_intel.c
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@ -71,7 +71,7 @@ static int fixed_pmc_events[] = {
static void reprogram_fixed_counters(struct kvm_pmu *pmu, u64 data)
{
struct kvm_pmc *pmc;
u8 old_fixed_ctr_ctrl = pmu->fixed_ctr_ctrl;
u64 old_fixed_ctr_ctrl = pmu->fixed_ctr_ctrl;
int i;
pmu->fixed_ctr_ctrl = data;