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

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Message-ID: <4B5510B1.9010202@zytor.com>
Date:	Mon, 18 Jan 2010 17:53:53 -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 12:50 AM, Gleb Natapov wrote:
> On Mon, Jan 18, 2010 at 12:34:16AM -0800, H. Peter Anvin wrote:
>> On 01/17/2010 06:44 AM, Gleb Natapov wrote:
>>> On Thu, Jan 14, 2010 at 06:31:07PM +0100, Peter Zijlstra wrote:
>>>> On Tue, 2010-01-05 at 16:12 +0200, Gleb Natapov wrote:
>>>>> Allow paravirtualized guest to do special handling for some page faults.
>>>>>
>>>>> The patch adds one 'if' to do_page_fault() function. The call is patched
>>>>> out when running on physical HW. I ran kernbech on the kernel with and
>>>>> without that additional 'if' and result were rawly the same:
>>>>
>>>> So why not program a different handler address for the #PF/#GP faults
>>>> and avoid the if all together?
>>> I would gladly use fault vector reserved by x86 architecture, but I am
>>> not sure Intel will be happy about it.
>>>
>>
>> That's what it's there for... see Peter Z.'s response.
>>
> Do you mean I can use one of exception vectors reserved by Intel
> (20-31)? What Peter Z says is that I can register my own handler for
> #PF and avoid the 'if' in non PV case as far as I understand him.
> 

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?

	-hpa

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

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