linux-kernel - Re: [RFC PATCH v2 13/32] KVM: SVM: Enable SEV by setting the SEV

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Message-ID: <20170309192919.lt3gfqeuhlsoylu7@pd.tnic>
Date:   Thu, 9 Mar 2017 20:29:19 +0100
From:   Borislav Petkov <bp@...e.de>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     simon.guinot@...uanux.org, linux-efi@...r.kernel.org,
        kvm@...r.kernel.org, rkrcmar@...hat.com, matt@...eblueprint.co.uk,
        linux-pci@...r.kernel.org, linus.walleij@...aro.org,
        gary.hook@....com, linux-mm@...ck.org,
        paul.gortmaker@...driver.com, hpa@...or.com, cl@...ux.com,
        dan.j.williams@...el.com, aarcange@...hat.com,
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        herbert@...dor.apana.org.au, bhe@...hat.com, xemul@...allels.com,
        joro@...tes.org, x86@...nel.org, peterz@...radead.org,
        piotr.luc@...el.com, mingo@...hat.com, msalter@...hat.com,
        ross.zwisler@...ux.intel.com, dyoung@...hat.com,
        thomas.lendacky@....com, jroedel@...e.de, keescook@...omium.org,
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        akpm@...ux-foundation.org, davem@...emloft.net
Subject: Re: [RFC PATCH v2 13/32] KVM: SVM: Enable SEV by setting the
 SEV_ENABLE CPU feature

On Thu, Mar 02, 2017 at 10:15:01AM -0500, Brijesh Singh wrote:
> From: Tom Lendacky <thomas.lendacky@....com>
> 
> Modify the SVM cpuid update function to indicate if Secure Encrypted
> Virtualization (SEV) is active in the guest by setting the SEV KVM CPU
> features bit. SEV is active if Secure Memory Encryption is enabled in
> the host and the SEV_ENABLE bit of the VMCB is set.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> ---
>  arch/x86/kvm/cpuid.c |    4 +++-
>  arch/x86/kvm/svm.c   |   18 ++++++++++++++++++
>  2 files changed, 21 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 1639de8..e0c40a8 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -601,7 +601,7 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
>  		entry->edx = 0;
>  		break;
>  	case 0x80000000:
> -		entry->eax = min(entry->eax, 0x8000001a);
> +		entry->eax = min(entry->eax, 0x8000001f);
>  		break;
>  	case 0x80000001:
>  		entry->edx &= kvm_cpuid_8000_0001_edx_x86_features;
> @@ -634,6 +634,8 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
>  		break;
>  	case 0x8000001d:
>  		break;
> +	case 0x8000001f:
> +		break;

I guess those three case's can be unified:

        case 0x8000001a:
        case 0x8000001d:
        case 0x8000001f:
                break;

...

> +	sev_info = kvm_find_cpuid_entry(vcpu, 0x8000001f, 0);
> +	if (!sev_info)
> +		return;
> +
> +	if (ca->nested_ctl & SVM_NESTED_CTL_SEV_ENABLE) {
> +		features->eax |= (1 << KVM_FEATURE_SEV);
> +		cpuid(0x8000001f, &sev_info->eax, &sev_info->ebx,
> +		      &sev_info->ecx, &sev_info->edx);
> +	}

Right, as already mentioned in the previous mail: can we communicate SEV
status to the guest solely through the 0x8000001f leaf? Then we won't
need KVM_FEATURE_SEV and this way we'll be hypervisor-agnostic, as Paolo
suggested.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--