Message-ID: <4B55E5D8.1070402@zytor.com>
Date: Tue, 19 Jan 2010 09:03:20 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Gleb Natapov <gleb@redhat.com>
CC: Peter Zijlstra <peterz@infradead.org>, kvm@vger.kernel.org,
       linux-mm@kvack.org, linux-kernel@vger.kernel.org, avi@redhat.com,
       mingo@elte.hu, tglx@linutronix.de, riel@redhat.com,
       cl@linux-foundation.org
Subject: Re: [PATCH v3 04/12] Add "handle page fault" PV helper.
References: <1262700774-1808-1-git-send-email-gleb@redhat.com> <1262700774-1808-5-git-send-email-gleb@redhat.com> <1263490267.4244.340.camel@laptop> <20100117144411.GI31692@redhat.com> <4B541D08.9040802@zytor.com> <20100118085022.GA30698@redhat.com> <4B5510B1.9010202@zytor.com> <20100119065537.GF14345@redhat.com>
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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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