linux-kernel - Re: [patch 6/6] x86/fpu: Provide kvm_sync_guest_vmexit_xfd

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Date:   Wed, 15 Dec 2021 10:49:18 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Liu, Jing2" <jing2.liu@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     Yang Zhong <yang.zhong@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>, x86@...nel.org,
        kvm@...r.kernel.org, Sean Christoperson <seanjc@...gle.com>,
        Jin Nakajima <jun.nakajima@...el.com>,
        Kevin Tian <kevin.tian@...el.com>
Subject: Re: [patch 6/6] x86/fpu: Provide kvm_sync_guest_vmexit_xfd_state()

Jing,

On Wed, Dec 15 2021 at 14:35, Jing2 Liu wrote:
> On 12/14/2021 10:50 AM, Thomas Gleixner wrote:
>> KVM can disable the write emulation for the XFD MSR when the vCPU's fpstate
>> is already correctly sized to reduce the overhead.
>>
>> When write emulation is disabled the XFD MSR state after a VMEXIT is
>> unknown and therefore not in sync with the software states in fpstate and
>> the per CPU XFD cache.
>>
>> Provide kvm_sync_guest_vmexit_xfd_state() which has to be invoked after a
>> VMEXIT before enabling interrupts when write emulation is disabled for the
>> XFD MSR.
> Thanks for this function.
>
> s/kvm_sync_guest_vmexit_xfd_state/fpu_sync_guest_vmexit_xfd_state
> in subject and changelog.

I clearly need more sleep.