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From:   "Liu, Jing2" <jing2.liu@intel.com>
To:     Thomas Gleixner <tglx@linutronix.de>,
        Paolo Bonzini <pbonzini@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>
CC:     "x86@kernel.org" <x86@kernel.org>,
        "Bae, Chang Seok" <chang.seok.bae@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "Arjan van de Ven" <arjan@linux.intel.com>,
        "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
        "Nakajima, Jun" <jun.nakajima@intel.com>,
        Jing Liu <jing2.liu@linux.intel.com>,
        "seanjc@google.com" <seanjc@google.com>,
        "Cooper, Andrew" <andrew.cooper3@citrix.com>
Subject: RE: [patch 13/31] x86/fpu: Move KVMs FPU swapping to FPU core
Thread-Topic: [patch 13/31] x86/fpu: Move KVMs FPU swapping to FPU core
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Date:   Fri, 15 Oct 2021 09:20:13 +0000
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On 10/15/2021 3:14 AM, Thomas Gleixner wrote:
> Paolo,
>=20
[...]
> >> vcpu_create()
> >>
> >>    fpu_init_fpstate_user(guest_fpu, supported_xcr0)
> >>
> >> That will (it does not today) do:
> >>
> >>       guest_fpu::__state_perm =3D supported_xcr0 &
> >> xstate_get_group_perm();
> >>
> >> The you have the information you need right in the guest FPU.
> >
> > Good, I wasn't aware of the APIs that will be there.
>=20
> Me neither, but that's a pretty obvious consequence of the work I'm doing
> for AMX. So I made it up for you. :)

Do you mean that fpu_init_fpstate_user() will be updated to add
supported_xcr0 later? :)=20

I'm thinking if guest_fpu::xfd is good to directly initialize as user's
init_fpstate.xfd. Because before guest initializes XFD, "hardware"
is reset value. So it would be better to make guest_fpu::xfd the
same so no need to reload zero before vmenter during this time.

Thanks,
Jing