linux-kernel - Re: [regression] commit d298b03506d3 ("x86/fpu: Restore the masking out of reserved MXCSR bits")

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Message-ID: <YWhG0kv/d/hddf+t@intel.com>
Date:   Thu, 14 Oct 2021 18:03:46 +0300
From:   Ville Syrjälä <ville.syrjala@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Ser Olmy <ser.olmy@...tonmail.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [regression] commit d298b03506d3 ("x86/fpu: Restore the masking
 out of reserved MXCSR bits")

On Thu, Oct 14, 2021 at 04:56:56PM +0200, Borislav Petkov wrote:
> On Thu, Oct 14, 2021 at 05:43:14PM +0300, Ville Syrjälä wrote:
> > Hmm. Actually I just stared at the code a bit more it looks
> > a bit funny. Was it supposed to do this instead?
> > 
> > - fpu->state.fxsave.mxcsr &= ~mxcsr_feature_mask;
> > + fpu->state.fxsave.mxcsr &= mxcsr_feature_mask;
> 
> Whoops, I had it like that in the original patch:
> 
> https://lore.kernel.org/all/163354193576.25758.8132624386883258818.tip-bot2@tip-bot2/
> 
> I blame tglx. :-)
> 
> Does it work if you remove the mask negation "~"?

The machine is currently preoccupied with other things. Should free up
in an hour or two. Once it does I'll give this a spin and report back.

-- 
Ville Syrjälä
Intel