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

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Message-ID: <4B55E5D8.1070402@zytor.com>
Date:	Tue, 19 Jan 2010 09:03:20 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Gleb Natapov <gleb@...hat.com>
CC:	Peter Zijlstra <peterz@...radead.org>, kvm@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org, avi@...hat.com,
	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 01/18/2010 10:55 PM, Gleb Natapov wrote:
>>
>> What I mean is that vector 14 is page faults -- that's what it is all
>> about.  Why on Earth do you need another vector?
>>
> Because this is not usual pagefault that tell the OS that page is not
> mapped. This is a notification to a guest OS that the page it is trying
> to access is swapped out by the host OS. There is nothing guest can do
> about it except schedule another task. So the guest should handle both
> type of exceptions: usual #PF when page is not mapped by the guest and
> new type of notifications. Ideally we would use one of unused exception
> vectors for new type of notifications.
> 

Ah, this kind of stuff.  We have talked about this in the past, and the
right way to do that is to have the guest OS pick a vector our of the
standard 0x20-0xff range, and then notify the hypervisor via a hypercall
which vector to use.

In Linux this means marking it as a system vector.  Note that there are
real hardware system vectors which will be mutually exclusive with this,
e.g. the UV one.

	-hpa

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

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