linux-kernel - RE: [patch 13/31] x86/fpu: Move KVMs FPU swapping to FPU core

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Date:   Wed, 13 Oct 2021 17:12:15 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Liu, Jing2" <jing2.liu@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     "x86@...nel.org" <x86@...nel.org>,
        "Bae, Chang Seok" <chang.seok.bae@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Nakajima, Jun" <jun.nakajima@...el.com>,
        Jing Liu <jing2.liu@...ux.intel.com>,
        "seanjc@...gle.com" <seanjc@...gle.com>
Subject: RE: [patch 13/31] x86/fpu: Move KVMs FPU swapping to FPU core

Jing,

On Wed, Oct 13 2021 at 06:15, Jing2 Liu wrote:
>> On 12/10/21 02:00, Thomas Gleixner wrote:
> When looking into the tglx/devel.git x86/fpu for the full #1-#4 
> series and the KVM AMX support, I'd like to talk two things
>  as follows,
>
> 1. KVM dynamic allocation API:
> Since KVM also uses dynamic allocation, after KVM detects guest
> requesting AMX by #NM trap, KVM need alloc extra buffer for
> this vcpu's current->thread.fpu.fpstate and guest_fpu related.
> So far, the kernel itself has such API like fpstate_realloc(), but it's
> static. How about making a common function usable for KVM?

Just making that function usable without a proper design how this should
work at all does not solve anything.

We first need a conclusion vs. buffer reallocation.

Once that is sorted then we can create proper infrastructure for that in
the FPU core code and not just expose a random function to KVM and hack
it into submssion.

Thanks,

        tglx