linux-kernel - Re: [patch 0/6] x86/fpu: Preparatory changes for guest AMX support

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Message-ID: <09e06d62-33f5-b41f-e913-a8c5e43ba881@redhat.com>
Date:   Tue, 14 Dec 2021 11:42:36 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     Jing Liu <jing2.liu@...ux.intel.com>,
        Yang Zhong <yang.zhong@...el.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 0/6] x86/fpu: Preparatory changes for guest AMX support

On 12/14/21 03:50, Thomas Gleixner wrote:
> The only remaining issue is the KVM XSTATE save/restore size checking which
> probably requires some FPU core assistance. But that requires some more
> thoughts vs. the IOCTL interface extension and once that is settled it
> needs to be solved in one go. But that's an orthogonal issue to the above.

That's not a big deal because KVM uses the uncompacted format.  So 
KVM_CHECK_EXTENSION and KVM_GET_XSAVE can just use CPUID to retrieve the 
size and uncompacted offset of the largest bit that is set in 
kvm_supported_xcr0, while KVM_SET_XSAVE can do the same with the largest 
bit that is set in the xstate_bv.

Paolo



> The series is also available from git:
> 
>     git://git.kernel.org/pub/scm/linux/kernel/git/people/tglx/devel.git x86/fpu-kvm