linux-kernel - Re: [RFC PATCH 20/35] KVM: SVM: Add SEV/SEV-ES support for intercepting INVD

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Date:   Mon, 14 Sep 2020 15:00:52 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [RFC PATCH 20/35] KVM: SVM: Add SEV/SEV-ES support for
 intercepting INVD

On Mon, Sep 14, 2020 at 03:15:34PM -0500, Tom Lendacky wrote:
> From: Tom Lendacky <thomas.lendacky@....com>
> 
> The INVD instruction intercept performs emulation. Emulation can't be done
> on an SEV or SEV-ES guest because the guest memory is encrypted.
> 
> Provide a specific intercept routine for the INVD intercept. Within this
> intercept routine, skip the instruction for an SEV or SEV-ES guest since
> it is emulated as a NOP anyway.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> ---
>  arch/x86/kvm/svm/svm.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 37c98e85aa62..ac64a5b128b2 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -2275,6 +2275,17 @@ static int iret_interception(struct vcpu_svm *svm)
>  	return 1;
>  }
>  
> +static int invd_interception(struct vcpu_svm *svm)
> +{
> +	/*
> +	 * Can't do emulation on any type of SEV guest and INVD is emulated
> +	 * as a NOP, so just skip it.
> +	 */
> +	return (sev_guest(svm->vcpu.kvm))

Should this be a standalone/backported fix for SEV?

> +		? kvm_skip_emulated_instruction(&svm->vcpu)
> +		: kvm_emulate_instruction(&svm->vcpu, 0);
> +}
> +
>  static int invlpg_interception(struct vcpu_svm *svm)
>  {
>  	if (!static_cpu_has(X86_FEATURE_DECODEASSISTS))
> @@ -2912,7 +2923,7 @@ static int (*const svm_exit_handlers[])(struct vcpu_svm *svm) = {
>  	[SVM_EXIT_RDPMC]			= rdpmc_interception,
>  	[SVM_EXIT_CPUID]			= cpuid_interception,
>  	[SVM_EXIT_IRET]                         = iret_interception,
> -	[SVM_EXIT_INVD]                         = emulate_on_interception,
> +	[SVM_EXIT_INVD]                         = invd_interception,
>  	[SVM_EXIT_PAUSE]			= pause_interception,
>  	[SVM_EXIT_HLT]				= halt_interception,
>  	[SVM_EXIT_INVLPG]			= invlpg_interception,
> -- 
> 2.28.0
>