linux-kernel - Re: [patch] x86, mm: avoid stale tlb entries by clearing prev mm

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Date:	Thu, 3 Feb 2011 22:06:16 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	"Mallick, Asit K" <asit.k.mallick@...el.com>
Subject: Re: [patch] x86, mm: avoid stale tlb entries by clearing prev
 mm_cpumask after switching mm


* Suresh Siddha <suresh.b.siddha@...el.com> wrote:

> On Thu, 2011-02-03 at 11:48 -0800, Linus Torvalds wrote:
> > On Thu, Feb 3, 2011 at 11:34 AM, Suresh Siddha
> > <suresh.b.siddha@...el.com> wrote:
> > >
> > > True. 'stale' is the wrong word. Do you want me to send a corrected one
> > > by replacing it with 'bogus'?
> > 
> > Please.
> > 
> > > my understanding is that unless we end up using that TLB entry, we will
> > > not have the issues like machine checks due to cacheability issues etc.
> > > If it is not global, upcoming cr3 change will flush it and meanwhile I
> > > don't think there is a scenario where we refer to these user-addresses.
> > 
> > Quite possible. The situation I envisioned was the same speculative
> > memory access that causes the TLB fill to also cause a cache fill -
> > for a noncacheable region (because the bogus TLB entry sets the random
> > address to cacheable).
> > 
> > And then what happens when somebody else accesses the same memory
> > noncacheably (through a valid TLB entry), and finds it in the cache?
> > 
> > I dunno. Not really important. The important part is the "possible
> > random bogus TLB entry", the fact that the CPU can act strangely after
> > that is pretty much a given.
> > 
> 
> Ok. Updated patch appended.

Linus, the patch fine to me too.

Acked-by: Ingo Molnar <mingo@...e.hu>

Do you want to apply it or should I?

Thanks,

	Ingo
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