linux-kernel - Re: [PATCH 3/9] KVM: x86: SVM: Pass through shadow stack MSRs

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Message-ID: <8484053f-2777-eb55-a30c-64125fbfc3ec@amd.com>
Date:   Thu, 12 Oct 2023 14:31:19 +0530
From:   "Nikunj A. Dadhania" <nikunj@....com>
To:     John Allen <john.allen@....com>, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, pbonzini@...hat.com,
        weijiang.yang@...el.com, rick.p.edgecombe@...el.com,
        seanjc@...gle.com, x86@...nel.org, thomas.lendacky@....com,
        bp@...en8.de
Subject: Re: [PATCH 3/9] KVM: x86: SVM: Pass through shadow stack MSRs

On 10/11/2023 1:32 AM, John Allen wrote:
> If kvm supports shadow stack, pass through shadow stack MSRs to improve
> guest performance.
> 
> Signed-off-by: John Allen <john.allen@....com>
> ---
>  arch/x86/kvm/svm/svm.c | 26 ++++++++++++++++++++++++++
>  arch/x86/kvm/svm/svm.h |  2 +-
>  2 files changed, 27 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index e435e4fbadda..984e89d7a734 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -139,6 +139,13 @@ static const struct svm_direct_access_msrs {
>  	{ .index = X2APIC_MSR(APIC_TMICT),		.always = false },
>  	{ .index = X2APIC_MSR(APIC_TMCCT),		.always = false },
>  	{ .index = X2APIC_MSR(APIC_TDCR),		.always = false },
> +	{ .index = MSR_IA32_U_CET,                      .always = false },
> +	{ .index = MSR_IA32_S_CET,                      .always = false },
> +	{ .index = MSR_IA32_INT_SSP_TAB,                .always = false },
> +	{ .index = MSR_IA32_PL0_SSP,                    .always = false },
> +	{ .index = MSR_IA32_PL1_SSP,                    .always = false },
> +	{ .index = MSR_IA32_PL2_SSP,                    .always = false },
> +	{ .index = MSR_IA32_PL3_SSP,                    .always = false },

First three MSRs are emulated in the patch 1, any specific reason for skipping MSR_IA32_PL[0-3]_SSP ?

Regards,
Nikunj