linux-kernel - Re: [PATCH 1/2] x86/mm: Reinitialize TLB state on hotplug and resume

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Date:   Thu, 7 Sep 2017 09:31:07 +0200 (CEST)
From:   Jiri Kosina <jikos@...nel.org>
To:     Andy Lutomirski <luto@...nel.org>
cc:     X86 ML <x86@...nel.org>, Borislav Petkov <bpetkov@...e.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH 1/2] x86/mm: Reinitialize TLB state on hotplug and
 resume

On Wed, 6 Sep 2017, Andy Lutomirski wrote:

> When Linux brings a CPU down and back up, it switches to init_mm and then
> loads swapper_pg_dir into CR3.  With PCID enabled, this has the side effect
> of masking off the ASID bits in CR3.
> 
> This can result in some confusion in the TLB handling code.  If we
> bring a CPU down and back up with any ASID other than 0, we end up
> with the wrong ASID active on the CPU after resume.  This could
> cause our internal state to become corrupt, although major
> corruption is unlikely because init_mm doesn't have any user pages.
> More obviously, if CONFIG_DEBUG_VM=y, we'll trip over an assertion
> in the next context switch.  The result of *that* is a failure to
> resume from suspend with probability 1 - 1/6^(cpus-1).
> 
> Fix it by reinitializing cpu_tlbstate on resume and CPU bringup.
> 
> Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Reported-by: Jiri Kosina <jikos@...nel.org>
> Fixes: 10af6235e0d3 ("x86/mm: Implement PCID based optimization: try to preserve old TLB entries using PCID")
> Signed-off-by: Andy Lutomirski <luto@...nel.org>

Tested-by: Jiri Kosina <jkosina@...e.cz>

Thanks,

-- 
Jiri Kosina
SUSE Labs