linux-kernel - Re: [PATCH Part2 RFC v4 02/40] KVM: SVM: Provide the Hypervisor Feature support VMGEXIT

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Message-ID: <YO9K8akh1CdY1kjd@google.com>
Date:   Wed, 14 Jul 2021 20:37:05 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Borislav Petkov <bp@...en8.de>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>, tony.luck@...el.com,
        npmccallum@...hat.com, brijesh.ksingh@...il.com
Subject: Re: [PATCH Part2 RFC v4 02/40] KVM: SVM: Provide the Hypervisor
 Feature support VMGEXIT

On Wed, Jul 07, 2021, Brijesh Singh wrote:
> Version 2 of the GHCB specification introduced advertisement of features
> that are supported by the Hypervisor.
> 
> Now that KVM supports version 2 of the GHCB specification, bump the
> maximum supported protocol version.

Heh, the changelog doesn't actually state that it's adding support for said
advertisement of features.  It took me a few seconds to figure out what the
patch was doing, even though it's quite trivial in the end.

> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> ---
>  arch/x86/include/uapi/asm/svm.h |  4 ++--
>  arch/x86/kvm/svm/sev.c          | 14 ++++++++++++++
>  arch/x86/kvm/svm/svm.h          |  3 ++-
>  3 files changed, 18 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/include/uapi/asm/svm.h b/arch/x86/include/uapi/asm/svm.h
> index 9aaf0ab386ef..ba4137abf012 100644
> --- a/arch/x86/include/uapi/asm/svm.h
> +++ b/arch/x86/include/uapi/asm/svm.h
> @@ -115,7 +115,7 @@
>  #define SVM_VMGEXIT_AP_CREATE_ON_INIT		0
>  #define SVM_VMGEXIT_AP_CREATE			1
>  #define SVM_VMGEXIT_AP_DESTROY			2
> -#define SVM_VMGEXIT_HYPERVISOR_FEATURES		0x8000fffd
> +#define SVM_VMGEXIT_HV_FT			0x8000fffd

This is fixing up commit 3 from Part1, though I think it can and should be
omitted from that patch entirely since it's not relevant to the guest, only to
KVM.

And FWIW, I like the verbose name, though it looks like Boris requested the
shorter names for the guest.  Can we keep the verbose form for KVM-only VMEGXIT
name?  Hyper-V has mostly laid claim to "HV", and feature is not the first thing
that comes to mind for "FT".

>  #define SVM_VMGEXIT_UNSUPPORTED_EVENT		0x8000ffff