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

From: Borislav Petkov
Date: Tue Sep 14 2021 - 04:28:24 EST

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@xxxxxxxxx>)

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@xxxxxxxxxxxxxxx>
> Fixes: 5567d11c21a1 ("x86/mce: Send #MC singal from task work")

Ah ok, that one makes sense.

> Signed-off-by: Tony Luck <tony.luck@xxxxxxxxx>
> ---
> > 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.