From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Roedel, Joerg" Subject: Re: [PATCH] KVM: MMU: Do not unconditionally read PDPTE from guest memory Date: Tue, 2 Aug 2011 15:11:25 +0200 Message-ID: <20110802131125.GR5176@amd.com> References: <1311842177-9542-1-git-send-email-avi@redhat.com> <20110729113111.GL5176@amd.com> <4E350D8C.7060508@redhat.com> <20110802093109.GP5176@amd.com> <4E37EED8.6030203@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Cc: Marcelo Tosatti , "kvm@vger.kernel.org" To: Avi Kivity Return-path: Received: from va3ehsobe002.messaging.microsoft.com ([216.32.180.12]:49138 "EHLO VA3EHSOBE002.bigfish.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754497Ab1HBNLk (ORCPT ); Tue, 2 Aug 2011 09:11:40 -0400 Content-Disposition: inline In-Reply-To: <4E37EED8.6030203@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Tue, Aug 02, 2011 at 08:34:32AM -0400, Avi Kivity wrote: > On 08/02/2011 12:31 PM, Roedel, Joerg wrote: > > On Sun, Jul 31, 2011 at 04:08:44AM -0400, Avi Kivity wrote: > > > On 07/29/2011 02:31 PM, Roedel, Joerg wrote: > > > > On Thu, Jul 28, 2011 at 04:36:17AM -0400, Avi Kivity wrote: > > > > > Architecturally, PDPTEs are cached in the PDPTRs when CR3 is reloaded. > > > > > On SVM, it is not possible to implement this, but on VMX this is possible > > > > > and was indeed implemented until nested SVM changed this to unconditionally > > > > > read PDPTEs dynamically. This has noticable impact when running PAE guests. > > > > > > > > > > Fix by changing the MMU to read PDPTRs from the cache, falling back to > > > > > reading from memory for the nested MMU. > > > > > > > > > > Signed-off-by: Avi Kivity > > > > > > > > Hmm, interesting. Sorry for breaking it. I tested the patch on nested > > > > svm, it works fine. > > > > > > Does pae-on-pae work for you? > > > > Only tested pae-on-longmode. I'll see if I can find my 32bit > > installation again and test this too. > > I wanted to test it since any mixup in where the PTPTRs were taken from > would be readily apparent. But it crashes even without the patch. Hmm, it worked when it was merged. I'll take a look at it. Joerg -- AMD Operating System Research Center Advanced Micro Devices GmbH Einsteinring 24 85609 Dornach General Managers: Alberto Bozzo, Andrew Bowd Registration: Dornach, Landkr. Muenchen; Registerger. Muenchen, HRB Nr. 43632