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Date: Mon, 02 Nov 2009 21:33:45 +0200
From: Avi Kivity <avi@redhat.com>
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To: Rik van Riel <riel@redhat.com>
CC: Ingo Molnar <mingo@elte.hu>, Gleb Natapov <gleb@redhat.com>,
       kvm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org,
       "H. Peter Anvin" <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 02/11] Add "handle page fault" PV helper.
References: <1257076590-29559-1-git-send-email-gleb@redhat.com> <1257076590-29559-3-git-send-email-gleb@redhat.com> <20091102092214.GB8933@elte.hu> <4AEF2D0A.4070807@redhat.com>
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On 11/02/2009 09:03 PM, Rik van Riel wrote:
>> This patch is not acceptable unless it's done cleaner. Currently we
>> already have 3 callbacks in do_page_fault() (kmemcheck, mmiotrace,
>> notifier), and this adds a fourth one.
>
>
> There's another alternative - add our own exception vector
> for async page faults.  Not sure if that is warranted though,
> especially if we already have other callbacks in do_page_fault()
> and we can consolidate them.
>

We can't add an exception vector since all the existing ones are either 
taken or reserved.  We can try to use an interrupt vector as an 
exception, but that becomes messy, and I'm not sure hardware will allow 
us to inject an interrupt when interrupts are disabled.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.