linux-kernel - Re: [patch V2 45/52] x86/fpu: Dont restore PKRU in fpregs_restore

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Date:   Wed, 16 Jun 2021 10:56:27 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Yu\, Yu-cheng" <yu-cheng.yu@...el.com>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Borislav Petkov <bp@...e.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Kan Liang <kan.liang@...ux.intel.com>
Subject: Re: [patch V2 45/52] x86/fpu: Dont restore PKRU in fpregs_restore_userspace()

On Tue, Jun 15 2021 at 17:52, Yu-cheng Yu wrote:
> On 6/14/2021 8:44 AM, Thomas Gleixner wrote:
>> +		 * If PKRU is enabled, then the PKRU value is already
>> +		 * correct because it was either set in switch_to() or in
>> +		 * flush_thread(). So it is excluded because it might be
>> +		 * not up to date in current->thread.fpu.xsave state.
>> +		 */
>> +		__restore_fpregs_from_fpstate(&fpu->state,
>> +					      xfeatures_mask_restore_user());
>
> This needs to be xfeatures_mask_restore_user() | 
> xfeatures_mask_supervisor().

Indeed. Good catch!

Thanks,

        tglx