linux-kernel - Re: [PATCH v3 10/21] x86/fpu/xstate: Update xstate save function to support dynamic xstate

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Date:   Tue, 9 Feb 2021 15:48:42 +0000
From:   "Bae, Chang Seok" <chang.seok.bae@...el.com>
To:     Borislav Petkov <bp@...e.de>
CC:     Andy Lutomirski <luto@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "Brown, Len" <len.brown@...el.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "Liu, Jing2" <jing2.liu@...el.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [PATCH v3 10/21] x86/fpu/xstate: Update xstate save function to
 support dynamic xstate

On Feb 8, 2021, at 04:33, Borislav Petkov <bp@...e.de> wrote:
> On Wed, Dec 23, 2020 at 07:57:06AM -0800, Chang S. Bae wrote:
>> copy_xregs_to_kernel() used to save all user states in a kernel buffer.
>> When the dynamic user state is enabled, it becomes conditional which state
>> to be saved.
>> 
>> fpu->state_mask can indicate which state components are reserved to be
>> saved in XSAVE buffer. Use it as XSAVE's instruction mask to select states.
>> 
>> KVM used to save all xstate via copy_xregs_to_kernel(). Update KVM to set a
>> valid fpu->state_mask, which will be necessary to correctly handle dynamic
>> state buffers.
> 
> All this commit message should say is something along the lines of
> "extend copy_xregs_to_kernel() to receive a mask argument of which
> states to save, in preparation of dynamic states handling."

Yes, I will change like that. Thanks.

>> No functional change until the kernel supports dynamic user states.
> 
> Same comment as before.

This needs to be removed as per your comment [1].

Chang

[1] https://lore.kernel.org/lkml/20210209124906.GC15909@zn.tnic/