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

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Date:   Thu, 7 Sep 2017 09:48:34 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Jiri Kosina <jikos@...nel.org>
Cc:     Andy Lutomirski <luto@...nel.org>, 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


* Jiri Kosina <jikos@...nel.org> wrote:

> 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>

The fix should be upstream already, as of 1c9fe4409ce3 and later.

Thanks,

	Ingo