linux-kernel - Re: [PATCH 2/2] KVM: x86: Don't allow tsc_offset, tsc_scaling

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Message-ID: <Z9N6xWQV6e5Tufy4@ls.amr.corp.intel.com>
Date: Thu, 13 Mar 2025 17:39:33 -0700
From: Isaku Yamahata <isaku.yamahata@...el.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: Isaku Yamahata <isaku.yamahata@...el.com>, kvm@...r.kernel.org,
	Sean Christopherson <seanjc@...gle.com>, chao.gao@...el.com,
	rick.p.edgecombe@...el.com, yan.y.zhao@...el.com,
	linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
	Nikunj A Dadhania <nikunj@....com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	isaku.yamahata@...ux.intel.com
Subject: Re: [PATCH 2/2] KVM: x86: Don't allow tsc_offset, tsc_scaling_ratio
 to change

On Wed, Mar 12, 2025 at 01:24:32PM +0100,
Paolo Bonzini <pbonzini@...hat.com> wrote:

> On 10/12/24 09:55, Isaku Yamahata wrote:
> > Add guest_tsc_protected member to struct kvm_arch_vcpu and prohibit
> > changing TSC offset/multiplier when guest_tsc_protected is true.
> 
> Thanks Isaku!  To match the behavior of the SEV-SNP patches, this is
> also needed, which I have added to kvm-coco-queue:
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index dc2f14a6d8a1..ccde7c2b2248 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -3919,7 +3925,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  	case MSR_IA32_TSC:
>  		if (msr_info->host_initiated) {
>  			kvm_synchronize_tsc(vcpu, &data);
> -		} else {
> +		} else if (!vcpu->arch.guest_tsc_protected) {
>  			u64 adj = kvm_compute_l1_tsc_offset(vcpu, data) - vcpu->arch.l1_tsc_offset;
>  			adjust_tsc_offset_guest(vcpu, adj);
>  			vcpu->arch.ia32_tsc_adjust_msr += adj;

Thank you for catching this. This looks good.
-- 
Isaku Yamahata <isaku.yamahata@...el.com>