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 16:27:07 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Ville Syrjälä <ville.syrjala@...ux.intel.com>
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 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?

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?

-- 
Regards/Gruss,
    Boris.

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