From xen-devel-bounces@lists.xen.org Mon Feb 10 10:47:30 2014 Received: (at maildrop) by bugs.xenproject.org; 10 Feb 2014 10:47:30 +0000 Received: from lists.xen.org ([50.57.142.19]) by bugs.xenproject.org with esmtp (Exim 4.80) (envelope-from ) id 1WCoOg-00050v-7H for xen-devel-maildrop-Eithu9ie@bugs.xenproject.org; Mon, 10 Feb 2014 10:47:30 +0000 Received: from localhost ([127.0.0.1] helo=lists.xen.org) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1WCoJn-0004Rh-4Z; Mon, 10 Feb 2014 10:42:27 +0000 Received: from mail6.bemta5.messagelabs.com ([195.245.231.135]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1WCoJl-0004RY-P7 for xen-devel@lists.xen.org; Mon, 10 Feb 2014 10:42:25 +0000 Received: from [85.158.139.211:27257] by server-3.bemta-5.messagelabs.com id DE/79-13671-01DA8F25; Mon, 10 Feb 2014 10:42:24 +0000 X-Env-Sender: Andrew.Cooper3@citrix.com X-Msg-Ref: server-9.tower-206.messagelabs.com!1392028942!2810580!1 X-Originating-IP: [66.165.176.63] X-SpamReason: No, hits=0.0 required=7.0 tests=sa_preprocessor: VHJ1c3RlZCBJUDogNjYuMTY1LjE3Ni42MyA9PiAzMDYwNDg=\n X-StarScan-Received: X-StarScan-Version: 6.9.16; banners=-,-,- X-VirusChecked: Checked Received: (qmail 3611 invoked from network); 10 Feb 2014 10:42:24 -0000 Received: from smtp02.citrix.com (HELO SMTP02.CITRIX.COM) (66.165.176.63) by server-9.tower-206.messagelabs.com with RC4-SHA encrypted SMTP; 10 Feb 2014 10:42:24 -0000 X-IronPort-AV: E=Sophos;i="4.95,817,1384300800"; d="scan'208";a="99428498" Received: from accessns.citrite.net (HELO FTLPEX01CL01.citrite.net) ([10.9.154.239]) by FTLPIPO02.CITRIX.COM with ESMTP; 10 Feb 2014 10:42:05 +0000 Received: from ukmail1.uk.xensource.com (10.80.16.128) by smtprelay.citrix.com (10.13.107.78) with Microsoft SMTP Server id 14.2.342.4; Mon, 10 Feb 2014 05:42:05 -0500 Received: from andrewcoop.uk.xensource.com ([10.80.2.18]) by ukmail1.uk.xensource.com with esmtp (Exim 4.69) (envelope-from ) id 1WCoJR-0006ob-BY; Mon, 10 Feb 2014 10:42:05 +0000 Message-ID: <52F8ACFD.7090801@citrix.com> Date: Mon, 10 Feb 2014 10:42:05 +0000 From: Andrew Cooper User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20131103 Icedove/17.0.10 MIME-Version: 1.0 To: Tim Deegan References: <1392012840-22555-1-git-send-email-yang.z.zhang@intel.com> <20140210080314.GA758@deinos.phlegethon.org> In-Reply-To: <20140210080314.GA758@deinos.phlegethon.org> X-Enigmail-Version: 1.6 X-DLP: MIA1 Cc: Yang Zhang , xiantao.zhang@intel.com, JBeulich@suse.com, xen-devel@lists.xen.org Subject: Re: [Xen-devel] [PATCH] Don't track all memory when enabling log dirty to track vram X-BeenThere: xen-devel@lists.xen.org X-Mailman-Version: 2.1.13 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org On 10/02/14 08:03, Tim Deegan wrote: > At 14:14 +0800 on 10 Feb (1392038040), Yang Zhang wrote: >> From: Yang Zhang >> >> When enabling log dirty mode, it sets all guest's memory to readonly. >> And in HAP enabled domain, it modifies all EPT entries to clear write bit >> to make sure it is readonly. This will cause problem if VT-d shares page >> table with EPT: the device may issue a DMA write request, then VT-d engine >> tells it the target memory is readonly and result in VT-d fault. > So that's a problem even if only the VGA framebuffer is being tracked > -- DMA from a passthrough device will either cause a spurious error or > fail to update the dirt bitmap. > > I think it would be better not to allow VT-d and EPT to share > pagetables in cases where devices are passed through (i.e. all cases > where VT-d is in use). > > Tim. Sadly, this would make shared VT-d/EPT completely pointless as a feature, causing extra memory overhead in Xen by having to maintain EPT and IOMMU tables separately. Any usecase which doesn't involve dirty vram tracking (e.g. headless VM with SRIOV, PVH dom0) would be adversely affected. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel