linux-kernel - Re: [PATCH v11 19/23] KVM: x86: Enable CET virtualization for VMX and advertise to userspace

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Message-ID: <aJPB8Jd5AFKdIua3@AUSJOHALLEN.amd.com>
Date: Wed, 6 Aug 2025 15:58:24 -0500
From: John Allen <john.allen@....com>
To: Chao Gao <chao.gao@...el.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org,
	seanjc@...gle.com, pbonzini@...hat.com, dave.hansen@...el.com,
	rick.p.edgecombe@...el.com, mlevitsk@...hat.com,
	weijiang.yang@...el.com, minipli@...ecurity.net, xin@...or.com,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v11 19/23] KVM: x86: Enable CET virtualization for VMX
 and advertise to userspace

On Fri, Jul 04, 2025 at 01:49:50AM -0700, Chao Gao wrote:
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 803574920e41..6375695ce285 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -5223,6 +5223,10 @@ static __init void svm_set_cpu_caps(void)
>  	kvm_caps.supported_perf_cap = 0;
>  	kvm_caps.supported_xss = 0;
>  
> +	/* KVM doesn't yet support CET virtualization for SVM. */
> +	kvm_cpu_cap_clear(X86_FEATURE_SHSTK);
> +	kvm_cpu_cap_clear(X86_FEATURE_IBT);
> +

Since AMD isn't supporting IBT, not sure if it makes sense to clear IBT
here since it doesn't look like we're clearing other features that we
don't support in hardware. For compatibility, my series just removes
both lines here, but the IBT clearing is probably not needed in this
series.

Thanks,
John