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KVM: SVM: fix tsc scaling cache logic

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[ Upstream commit 11d39e8cc43e1c6737af19ca9372e590061b5ad2 ]

SVM uses a per-cpu variable to cache the current value of the
tsc scaling multiplier msr on each cpu.

Commit 1ab9287add
("KVM: X86: Add vendor callbacks for writing the TSC multiplier")
broke this caching logic.

Refactor the code so that all TSC scaling multiplier writes go through
a single function which checks and updates the cache.

This fixes the following scenario:

1. A CPU runs a guest with some tsc scaling ratio.

2. New guest with different tsc scaling ratio starts on this CPU
   and terminates almost immediately.

   This ensures that the short running guest had set the tsc scaling ratio just
   once when it was set via KVM_SET_TSC_KHZ. Due to the bug,
   the per-cpu cache is not updated.

3. The original guest continues to run, it doesn't restore the msr
   value back to its own value, because the cache matches,
   and thus continues to run with a wrong tsc scaling ratio.

Fixes: 1ab9287add ("KVM: X86: Add vendor callbacks for writing the TSC multiplier")
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20220606181149.103072-1-mlevitsk@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Maxim Levitsky
2022-06-06 21:11:49 +03:00
committed by Greg Kroah-Hartman
parent f0227eca97
commit 85ee9919ad
2 changed files with 24 additions and 11 deletions
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arch/x86/kvm/svm/svm.h
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@@ -487,6 +487,7 @@ int nested_svm_check_exception(struct vcpu_svm *svm, unsigned nr,
int nested_svm_exit_special(struct vcpu_svm *svm);
void nested_load_control_from_vmcb12(struct vcpu_svm *svm,
struct vmcb_control_area *control);
void __svm_write_tsc_multiplier(u64 multiplier);
void nested_sync_control_from_vmcb02(struct vcpu_svm *svm);
void nested_vmcb02_compute_g_pat(struct vcpu_svm *svm);
void svm_switch_vmcb(struct vcpu_svm *svm, struct kvm_vmcb_info *target_vmcb);