linux-kernel - Re: [patch 0/2] x86/alternatives: Prevent crash in NOP optimizer

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Date:   Fri, 8 Dec 2023 03:35:01 -0500
From:   Paul Gortmaker <paul.gortmaker@...driver.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        regressions@...mhuis.info, richard.purdie@...uxfoundation.org,
        regressions@...ts.linux.dev
Subject: Re: [patch 0/2] x86/alternatives: Prevent crash in NOP optimizer

[[patch 0/2] x86/alternatives: Prevent crash in NOP optimizer] On 07/12/2023 (Thu 20:49) Thomas Gleixner wrote:

> The following series addresses the regression report from Paul on behalf of
> the yocto project. It turns out that the recent changes to alternatives
> opened a race window where interrupts are enabled and NOPs are optimized in
> place. An interrupt hitting into the modification will observe inconsistent
> text and crash and burn.
> 
> A 32bit QEMU crashes w/o these fixes reliably within about 50 boot
> attempts. With the fix applied it survived close to 600 attempts by
> now.

I can confirm that - since I was already set up for it, I let it run
overnight for about 1250 attempts.  With an average of one in 200 that I
was seeing before, I should have had around six fails.  Didn't see one.

> Thanks to Paul for providing all the information!

On behalf of Richard and myself, thanks for the complex fix.

Paul.
--

> 
> Thanks,
> 
> 	tglx
> 
>