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From:   Jim Mattson <jmattson@google.com>
Date:   Wed, 25 Sep 2019 15:14:46 -0700
Message-ID: <CALMp9eTbaoCh=izdFHGEnX2-mBKZaWJ_Bkg3b53csVQgs+XmuQ@mail.gmail.com>
Subject: Re: [PATCH 1/2] KVM: x86: svm: Pass XSAVES to guest if available on host
To:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc:     kvm list <kvm@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        "the arch/x86 maintainers" <x86@kernel.org>
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On Wed, Sep 25, 2019 at 2:37 PM Sebastian Andrzej Siewior
<bigeasy@linutronix.de> wrote:
>
> In commit
>    55412b2eda2b7 ("kvm: x86: Add kvm_x86_ops hook that enables XSAVES for guest")
>
> XSAVES was enabled on VMX with a few additional tweaks and was always
> disabled on SVM. Before ZEN XSAVES was not available so it made no
> difference. With Zen it is possible to expose it to the guest if it is
> available on the host.
> I didn't find anything close to VMX's "VM-Execution Controls" and
> exposing this flag based on the CPUID flags cause no harm so far.
>
> Expose the XSAVES flag to the guest if the host supports it.
>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
>  arch/x86/kvm/svm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index e0368076a1ef9..3878eb766fa39 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -5992,7 +5992,7 @@ static bool svm_mpx_supported(void)
>
>  static bool svm_xsaves_supported(void)
>  {
> -       return false;
> +       return boot_cpu_has(X86_FEATURE_XSAVES);
>  }
>
>  static bool svm_umip_emulated(void)
> --
> 2.23.0

This is inadequate. Please read the existing thread, "[Patch] KVM:
SVM: Fix svm_xsaves_supported." Aaron Lewis is working on completing
this as we speak.