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KVM: SVM: Adjust tsc_offset only if tsc_unstable

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commit 953899b659 upstream.

The tsc_offset adjustment in svm_vcpu_load is executed
unconditionally even if Linux considers the host tsc as
stable. This causes a Linux guest detecting an unstable tsc
in any case.
This patch removes the tsc_offset adjustment if the host tsc
is stable. The guest will now get the benefit of a stable
tsc too.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Joerg Roedel
2010-10-28 16:48:13 -02:00
committed by Greg Kroah-Hartman
parent ffc109c28a
commit cd80c84027
1 changed files with 11 additions and 10 deletions
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21
arch/x86/kvm/svm.c
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@@ -795,17 +795,18 @@ static void svm_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
int i;
if (unlikely(cpu != vcpu->cpu)) {
u64 tsc_this, delta;
u64 delta;
/*
* Make sure that the guest sees a monotonically
* increasing TSC.
*/
rdtscll(tsc_this);
delta = vcpu->arch.host_tsc - tsc_this;
svm->vmcb->control.tsc_offset += delta;
if (is_nested(svm))
svm->nested.hsave->control.tsc_offset += delta;
if (check_tsc_unstable()) {
/*
* Make sure that the guest sees a monotonically
* increasing TSC.
*/
delta = vcpu->arch.host_tsc - native_read_tsc();
svm->vmcb->control.tsc_offset += delta;
if (is_nested(svm))
svm->nested.hsave->control.tsc_offset += delta;
}
vcpu->cpu = cpu;
kvm_migrate_timers(vcpu);
svm->asid_generation = 0;