From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with ESMTP id B132D6B007D for ; Thu, 21 Jan 2010 10:51:54 -0500 (EST) Message-ID: <4B58770A.3050107@zytor.com> Date: Thu, 21 Jan 2010 07:47:22 -0800 From: "H. Peter Anvin" MIME-Version: 1.0 Subject: Re: [PATCH v3 04/12] Add "handle page fault" PV helper. References: <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> <4B55E5D8.1070402@zytor.com> <20100119174438.GA19450@redhat.com> <4B5611A9.4050301@zytor.com> <20100120100254.GC5238@redhat.com> <4B5740CD.4020005@zytor.com> <4B58181B.60405@redhat.com> In-Reply-To: <4B58181B.60405@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Avi Kivity Cc: Gleb Natapov , Peter Zijlstra , kvm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, mingo@elte.hu, tglx@linutronix.de, riel@redhat.com, cl@linux-foundation.org List-ID: 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. -hpa -- H. Peter Anvin, Intel Open Source Technology Center I work for Intel. I don't speak on their behalf. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org