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

From: H. Peter Anvin
Date: Thu Jan 21 2010 - 10:52:55 EST

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.


H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.

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