Patch "KVM: x86: Use adjustment in guest cycles when handling MSR_IA32_TSC_ADJUST" has been added to the 4.1-stable tree

This is a note to let you know that I've just added the patch titled

KVM: x86: Use adjustment in guest cycles when handling MSR_IA32_TSC_ADJUST

to the 4.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kvm-x86-use-adjustment-in-guest-cycles-when-handling-msr_ia32_tsc_adjust.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Haozhong Zhang <[email protected]>
Date: Fri, 7 Aug 2015 11:24:32 +0800
Subject: KVM: x86: Use adjustment in guest cycles when handling MSR_IA32_TSC_ADJUST

From: Haozhong Zhang <[email protected]>

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.

---
 arch/x86/kvm/x86.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -2192,7 +2192,7 @@ int kvm_set_msr_common(struct kvm_vcpu *
 		if (guest_cpuid_has_tsc_adjust(vcpu)) {
 			if (!msr_info->host_initiated) {
 				s64 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;
 		}

Patches currently in stable-queue which might be from [email protected] are

queue-4.1/kvm-x86-use-adjustment-in-guest-cycles-when-handling-msr_ia32_tsc_adjust.patch