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From: Barret Rhoden <>
To: Borislav Petkov <>,
	Sebastian Andrzej Siewior <>
Cc: Josh Bleecher Snyder <>,
	"Rik van Riel\"" <>,,,
	Thomas Gleixner <>,
	Ingo Molnar <>,
Subject: Re: [PATCH] x86/fpu: Don't cache access to fpu_fpregs_owner_ctx
Date: Wed, 27 Nov 2019 13:42:47 -0500
Message-ID: <> (raw)
In-Reply-To: <20191127140754.GB3812@zn.tnic>

>> Use this_cpu_read() instead this_cpu_read_stable() to avoid caching of
>> fpu_fpregs_owner_ctx during preemption points.
>> Fixes: 5f409e20b7945 ("x86/fpu: Defer FPU state load until return to userspace")
> Or
> a352a3b7b792 ("x86/fpu: Prepare copy_fpstate_to_sigframe() for TIF_NEED_FPU_LOAD")
> maybe, which adds the fpregs_unlock() ?

Using this_cpu_read_stable() (or some variant) seems to go back quite a 
while; not sure when exactly it became a problem.  If it helps, commit 
d9c9ce34ed5c ("x86/fpu: Fault-in user stack if 
copy_fpstate_to_sigframe() fails") was the one that popped up the most 
during Austin's bisection.

>> Also I would like to add
>> 	Debugged-by: Ian Lance Taylor
> Yes, pls. CCed.

To close the loop on this, here's what Austin wrote on the bugzilla:

> --- Comment #2 from Austin Clements ( ---
> I can confirm that the patch posted by Sebastian Andrzej Siewior at
> fixes the issue both in our C reproducer
> and in our original Go reproducer. (Sorry, I'm not subscribed to LKML, so I
> can't reply there, and I'm on an airplane, so it's hard to get subscribed :)
> Regarding the question about the "Debugged-by" line in the patch, debugging was
> a joint effort between myself (Austin Clements <>), David
> Chase <>, and Ian Lance Taylor <>.



  reply index

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-26 19:49 AVX register corruption from signal delivery Barret Rhoden
2019-11-26 20:20 ` Sebastian Andrzej Siewior
2019-11-26 21:23   ` Barret Rhoden
2019-11-26 22:13     ` Borislav Petkov
2019-11-26 22:30       ` Andy Lutomirski
2019-11-26 23:00         ` Borislav Petkov
2019-11-27 12:42     ` [PATCH] x86/fpu: Don't cache access to fpu_fpregs_owner_ctx Sebastian Andrzej Siewior
2019-11-27 14:07       ` Borislav Petkov
2019-11-27 18:42         ` Barret Rhoden [this message]
2019-11-28  8:53           ` [PATCH v2] " Sebastian Andrzej Siewior
2019-11-28  9:22             ` [tip: x86/urgent] " tip-bot2 for Sebastian Andrzej Siewior
2019-11-29 16:57             ` [PATCH v2] " David Laight
2019-11-29 17:08               ` 'Sebastian Andrzej Siewior'
2019-11-27 15:46       ` [PATCH] " Rik van Riel

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