linux-kernel - Re: [PATCH v3 04/12] Add "handle page fault" PV helper.

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Date:	Fri, 22 Jan 2010 09:25:10 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Avi Kivity <avi@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
	kvm@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, mingo@...e.hu, tglx@...utronix.de,
	riel@...hat.com, cl@...ux-foundation.org
Subject: Re: [PATCH v3 04/12] Add "handle page fault" PV helper.

On Thu, Jan 21, 2010 at 07:47:22AM -0800, H. Peter Anvin wrote:
> On 01/21/2010 01:02 AM, Avi Kivity wrote:
> >>
> >> You can also just emulate the state transition -- since you know
> >> you're dealing with a flat protected-mode or long-mode OS (and just
> >> make that a condition of enabling the feature) you don't have to deal
> >> with all the strange combinations of directions that an unrestricted
> >> x86 event can take.  Since it's an exception, it is unconditional.
> > 
> > Do you mean create the stack frame manually?  I'd really like to avoid
> > that for many reasons, one of which is performance (need to do all the
> > virt-to-phys walks manually), the other is that we're certain to end up
> > with something horribly underspecified.  I'd really like to keep as
> > close as possible to the hardware.  For the alternative approach, see Xen.
> > 
> 
> I obviously didn't mean to do something which didn't look like a
> hardware-delivered exception.  That by itself provides a tight spec.
> The performance issue is real, of course.
> 
> Obviously, the design of VT-x was before my time at Intel, so I'm not
> familiar with why the tradeoffs that were done they way they were.
> 
Is it so out of question to reserver exception below 32 for PV use?

--
			Gleb.
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