On Wed, Sep 16, 2015 at 10:05:54PM -0700, gregkh@xxxxxxxxxxxxxxxxxxx wrote:
>
> The patch below does not apply to the 4.2-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@xxxxxxxxxxxxxxx>.
>
> thanks,
>
> greg k-h
>
Hi greg,
I found this patch is already in the 4.2-stable tree (commit id d7add05).
Thanks,
- Haozhong
> ------------------ original commit in Linus's tree ------------------
>
> From d7add05458084a5e3d65925764a02ca9c8202c1e Mon Sep 17 00:00:00 2001
> From: Haozhong Zhang <haozhong.zhang@xxxxxxxxx>
> Date: Fri, 7 Aug 2015 11:24:32 +0800
> Subject: [PATCH] KVM: x86: Use adjustment in guest cycles when handling
> MSR_IA32_TSC_ADJUST
>
> 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>
> Cc: stable@xxxxxxxxxxxxxx
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c5e88a881899..8f0f6eca69da 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2105,7 +2105,7 @@ 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) {
> 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;
> }
>
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