linux-kernel - Re: [PATCH v6 06/25] x86/fpu/xstate: Opt-in kernel dynamic bits when calculate guest xstate size

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Date:   Thu, 26 Oct 2023 22:06:56 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "Yang, Weijiang" <weijiang.yang@...el.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Gao, Chao" <chao.gao@...el.com>,
        "john.allen@....com" <john.allen@....com>,
        "peterz@...radead.org" <peterz@...radead.org>
Subject: Re: [PATCH v6 06/25] x86/fpu/xstate: Opt-in kernel dynamic bits when
 calculate guest xstate size

On Thu, 2023-10-26 at 10:24 -0700, Sean Christopherson wrote:
> +       /*
> +        * Calculate the resulting kernel state size.  Note,
> @permitted also
> +        * contains supervisor xfeatures even though supervisor are
> always
> +        * permitted for kernel and guest FPUs, and never permitted
> for user
> +        * FPUs.

What is a user FPU vs kernel FPU in this context? By user FPU do you
mean, like user FPU state in a sigframe or something? Or a kernel
task's FPU? If the former I think this comment could be made more
clear. Maybe just drop the bit about user FPUs. At least the comment
makes more sense to me without it.