Messages in this thread | | | Subject | Re: [PATCH] x86/fpu: Don't cache access to fpu_fpregs_owner_ctx | From | Barret Rhoden <> | Date | Wed, 27 Nov 2019 13:42:47 -0500 |
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>> 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 (austin@google.com) --- > I can confirm that the patch posted by Sebastian Andrzej Siewior at > https://lkml.org/lkml/2019/11/27/304 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 <austin@google.com>), David > Chase <drchase@golang.org>, and Ian Lance Taylor <ian@airs.com>.
Thanks,
Barret
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