linux-kernel - Re: [RFC PATCH 26/35] KVM: SVM: Guest FPU state save/restore not needed for SEV-ES guest

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Message-ID: <20200915163405.GD8420@sjchrist-ice>
Date:   Tue, 15 Sep 2020 09:34:05 -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 26/35] KVM: SVM: Guest FPU state save/restore not
 needed for SEV-ES guest

On Tue, Sep 15, 2020 at 09:25:18AM -0500, Tom Lendacky wrote:
> On 9/14/20 4:39 PM, Sean Christopherson wrote:
> > On Mon, Sep 14, 2020 at 03:15:40PM -0500, Tom Lendacky wrote:
> >> From: Tom Lendacky <thomas.lendacky@....com>
> >>
> >> The guest FPU is automatically restored on VMRUN and saved on VMEXIT by
> >> the hardware, so there is no reason to do this in KVM.
> > 
> > I assume hardware has its own buffer?  If so, a better approach would be to
> > not allocate arch.guest_fpu in the first place, and then rework KVM to key
> > off !guest_fpu.
> 
> Yup, let me look into that.

Heh, it's on our todo list as well :-)