linux-kernel - Re: [PATCH v2 06/39] x86/fpu: Add helper for modifying xstate

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Message-ID: <9246d8b4d968c258e60e5cced2adc4b04d257b9c.camel@intel.com>
Date:   Tue, 4 Oct 2022 16:13:41 +0000
From:   "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To:     "keescook@...omium.org" <keescook@...omium.org>,
        "Hansen, Dave" <dave.hansen@...el.com>
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Subject: Re: [PATCH v2 06/39] x86/fpu: Add helper for modifying xstate

On Tue, 2022-10-04 at 07:18 -0700, Dave Hansen wrote:
> On 10/3/22 13:05, Edgecombe, Rick P wrote:
> > The CET state is xsaves managed. It gets lazily restored before
> > returning to userspace with the rest of the fpu stuff. This
> > function
> > will force restore all the fpu state to the registers early and
> > lock
> > them from being automatically saved/restored. Then the tasks CET
> > state
> > can be modified in the MSRs, before unlocking the fpregs. Last time
> > I
> > tried to modify the state directly in the xsave buffer when it was
> > efficient, but it had issues and Thomas suggested this.
> 
> Can you get the gist of this in a comment, please?

Sure.