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

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Date:   Thu, 14 Oct 2021 17:34:14 +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 04:27:07PM +0200, Borislav Petkov wrote:
> On Thu, Oct 14, 2021 at 02:44:33PM +0300, Ville Syrjälä wrote:
> > I have a 32bit installation here that stopped working. Bisected it
> > to commit d298b03506d3 ("x86/fpu: Restore the masking out of reserved
> > MXCSR bits").
> 
> Lemme make sure I understand this correctly: this patch is bad and with
> it reverted it works?

Yes.

>
> Because before this patch, the restoring would be a more restrictive
> than before and this patch reverts the code to the old behavior for
> invalid MXCSR bits.
> 
> > Tested the same disk on on both a 64bit capable Pentium D
> > and a 32bit only Pentium 4 just to rule out the specific CPU.
> > Busted on both.
> 
> So that's a purely 32-bit installation and a 32-bit kernel and you've
> booted it on two different machines?

Yes.

-- 
Ville Syrjälä
Intel