linux-kernel - Re: [PATCH v2 8/8] x86/fpu/xstate: Restore supervisor xstates for __fpu__restore

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Message-ID: <20200306205039.GA5337@cz.tnic>
Date:   Fri, 6 Mar 2020 21:50:39 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v2 8/8] x86/fpu/xstate: Restore supervisor xstates for
 __fpu__restore_sig()

On Wed, Mar 04, 2020 at 10:18:46AM -0800, Yu-cheng Yu wrote:
> There is another way to keep this patch...
> 
> if (xfeatures_mask_supervisor()) {
> 	fpu->state.xsave.xfeatures &= xfeatures_mask_supervisor();

Is the subsequent XSAVE in copy_user_to_fpregs_zeroing() going to
restore the user bits in XSTATE_BV you just cleared?

Sorry, it looks like it would but the SDM text is abysmal.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette