linux-kernel - Re: [PATCH v3] x86/mce: Avoid infinite loop for copy from user recovery

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Message-ID: <YUBdGBRyMT0LCm1x@zn.tnic>
Date:   Tue, 14 Sep 2021 10:28:08 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Jue Wang <juew@...gle.com>, Ding Hui <dinghui@...gfor.com.cn>,
        naoya.horiguchi@....com, osalvador@...e.de,
        Youquan Song <youquan.song@...el.com>, huangcun@...gfor.com.cn,
        x86@...nel.org, linux-edac@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] x86/mce: Avoid infinite loop for copy from user
 recovery

On Mon, Sep 13, 2021 at 02:52:39PM -0700, Luck, Tony wrote:
> Also mark queue_task_work() as "noinstr" (as reported kernel test robot
> <lkp@...el.com>)

Yeah, that's not enough - I have a patchset in the works for all this so
I'm going to drop your annotation.

> Cc: <stable@...r.kernel.org>
> Fixes: 5567d11c21a1 ("x86/mce: Send #MC singal from task work")

Ah ok, that one makes sense.

> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
> 
> > What about a Fixes: tag?
> 
> Added a Fixes tag.
> 
> Also added "noinstr" to queue_task_work() per a kernel robot report.
> 
> Also re-wrote the commit comment (based on questions raised against v2)

Thanks - very much appreciated and it reads really good!

> > I guess backporting this to the respective kernels is predicated upon
> > the existence of those other "places" in the kernel where code assumes
> > the EFAULT was because of a #PF.
> 
> Not really. I don't expect to change any kernel code that just bounces
> off the same machine check a few times. This patch does work best in
> conjunction with patches 2 & 3 (unchanged, not reposted here). But it
> will fix some old issues even without those two.

Ok, got it.

/me queues.

-- 
Regards/Gruss,
    Boris.

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