linux-kernel - Re: [PATCH] x86/fpu/xstate: Fix XSTATE_WARN

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Date:   Wed, 28 Sep 2022 18:27:42 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Andrew Cooper <andrew.cooper3@...rix.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>
Subject: Re: [PATCH] x86/fpu/xstate: Fix XSTATE_WARN_ON() to emit relevant
 diagnostics

On Wed, Aug 10, 2022 at 11:19:09PM +0100, Andrew Cooper wrote:
> "XSAVE consistency problem" has been reported under Xen, but that's the extent
> of my divination skills.
> 
> Modify XSTATE_WARN_ON() to force the caller to provide relevant diagnostic
> information, and modify each caller suitably.
> 
> For check_xstate_against_struct(), this removes a double WARN() where one will
> do perfectly fine.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@...rix.com>
> ---
> CC: Thomas Gleixner <tglx@...utronix.de>
> CC: Ingo Molnar <mingo@...hat.com>
> CC: Borislav Petkov <bp@...en8.de>
> CC: Dave Hansen <dave.hansen@...ux.intel.com>
> CC: x86@...nel.org
> CC: Marek Marczykowski-Górecki <marmarek@...isiblethingslab.com>
> 
> RFC: CC stable?  This has been wonky debugging for 7 years.
> 
> Apparently "size 832 != kernel_size 0" so let the debugging continue...

I've got a similar bug report from people running Linux guest on some
other prop. HV. And I wanted to give them a debugging patch which dumps
*all* the relevant data along the path of paranoid_xstate_size_valid(),
the loop in there and xstate_calculate_size().

Looking how you might need something like that too, how about you extend
your patch to do that and have it being toggled on by a xstate=debug
cmdline?

It feels like this would be a useful thing to have with the gazillion of
XSTATE features and dynamic buffer allocation...

Thx.

-- 
Regards/Gruss,
    Boris.

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