[PATCH 3.16.y-ckt 094/130] KVM: x86: Use adjustment in guest cycles when handling MSR_IA32_TSC_ADJUST

From: Luis Henriques
Date: Fri Sep 04 2015 - 09:23:08 EST

3.16.7-ckt17 -stable review patch. If anyone has any objections, please let me know.


From: Haozhong Zhang <haozhong.zhang@xxxxxxxxx>

commit d7add05458084a5e3d65925764a02ca9c8202c1e upstream.

When kvm_set_msr_common() handles a guest's write to
MSR_IA32_TSC_ADJUST, it will calcuate an adjustment based on the data
written by guest and then use it to adjust TSC offset by calling a
call-back adjust_tsc_offset(). The 3rd parameter of adjust_tsc_offset()
indicates whether the adjustment is in host TSC cycles or in guest TSC
cycles. If SVM TSC scaling is enabled, adjust_tsc_offset()
[i.e. svm_adjust_tsc_offset()] will first scale the adjustment;
otherwise, it will just use the unscaled one. As the MSR write here
comes from the guest, the adjustment is in guest TSC cycles. However,
the current kvm_set_msr_common() uses it as a value in host TSC
cycles (by using true as the 3rd parameter of adjust_tsc_offset()),
which can result in an incorrect adjustment of TSC offset if SVM TSC
scaling is enabled. This patch fixes this problem.

Signed-off-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
arch/x86/kvm/x86.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e05ef62906f4..27a8d4f9bce5 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2099,7 +2099,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
if (guest_cpuid_has_tsc_adjust(vcpu)) {
if (!msr_info->host_initiated) {
u64 adj = data - vcpu->arch.ia32_tsc_adjust_msr;
- kvm_x86_ops->adjust_tsc_offset(vcpu, adj, true);
+ adjust_tsc_offset_guest(vcpu, adj);
vcpu->arch.ia32_tsc_adjust_msr = data;
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