linux-kernel - Re: PFs on pages pinned with get_user

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Date:	Thu, 29 Jan 2009 17:11:23 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frank Mehnert <Frank.Mehnert@....COM>
Cc:	linux-kernel@...r.kernel.org, Avi Kivity <avi@...hat.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: PFs on pages pinned with get_user_pages()

On Thu, 2009-01-29 at 17:03 +0100, Frank Mehnert wrote:
> On Thursday 29 January 2009, Peter Zijlstra wrote:
> > > > That aside, is there any reason you have to avoid scheduling? Otherwise
> > > > I would just allow so and be done with it.
> > >
> > > The reason is that our code expects that to ensure syncing of the CPU
> > > state with the saved state. I fear it is quite difficult to change
> > > that...
> >
> > Ah, is that what KVM uses the preempt notifiers for? Could you too?
> 
> Right, that could be an option.
> 
> We will try to change our code which is a big effort as we try
> to keep the code as unique as possible between the different
> hosts we support (Linux, Solaris, Windows, Mac OS X).
> 
> Just to be sure: There is no other option than disabling interrupts
> or calling disable_preemption() to prevent scheduling?

Thing is, lock_page() and down_read() require to be able to schedule(),
so there's no way around that.

So even if there was another way to disable scheduling, you'd still have
the same problem.

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