linux-kernel - Re: [PATCH v6 08/12] Handle async PF in a guest.

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Message-ID: <4CB0B8EF.3050702@redhat.com>
Date:	Sat, 09 Oct 2010 20:48:15 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Gleb Natapov <gleb@...hat.com>
CC:	kvm@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, mingo@...e.hu,
	a.p.zijlstra@...llo.nl, tglx@...utronix.de, hpa@...or.com,
	riel@...hat.com, cl@...ux-foundation.org, mtosatti@...hat.com
Subject: Re: [PATCH v6 08/12] Handle async PF in a guest.

  On 10/07/2010 08:03 PM, Gleb Natapov wrote:
> >  >>
> >  >Host side keeps track of outstanding apfs and will not send apf for the
> >  >same phys address twice. It will halt vcpu instead.
> >
> >  What about different pages, running the scheduler code?
> >
> We can get couple of nested apfs, just like we can get nested
> interrupts. Since scheduler disables preemption second apf will halt.

How much is a couple?

Consider:

SIGSTOP
Entire process swapped out
SIGCONT

We can get APF's on the current code, the scheduler code, the stack, any 
debugging code in between (e.g. ftrace), and the page tables for all of 
these.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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