Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752169AbbGOI44 (ORCPT ); Wed, 15 Jul 2015 04:56:56 -0400 Received: from smtp02.citrix.com ([66.165.176.63]:45365 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751032AbbGOI4y (ORCPT ); Wed, 15 Jul 2015 04:56:54 -0400 X-IronPort-AV: E=Sophos;i="5.15,479,1432598400"; d="scan'208";a="284233609" Message-ID: <55A62052.7020008@citrix.com> Date: Wed, 15 Jul 2015 10:56:50 +0200 From: Julien Grall User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Konrad Rzeszutek Wilk CC: , , , David Vrabel , , Boris Ostrovsky , Subject: Re: [Xen-devel] [PATCH v2 09/20] xen/biomerge: Don't allow biovec to be merge when Linux is not using 4KB page References: <1436474552-31789-1-git-send-email-julien.grall@citrix.com> <1436474552-31789-10-git-send-email-julien.grall@citrix.com> <20150710191245.GA31063@l.oracle.com> In-Reply-To: <20150710191245.GA31063@l.oracle.com> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-DLP: MIA2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1635 Lines: 45 Hi Konrad, On 10/07/2015 21:12, Konrad Rzeszutek Wilk wrote: > On Thu, Jul 09, 2015 at 09:42:21PM +0100, Julien Grall wrote: >> When Linux is using 64K page granularity, every page will be slipt in >> multiple non-contiguous 4K MFN (page granularity of Xen). > > But you don't care about that on the Linux layer I think? In general use case (i.e arch agnostic) we care about it. We don't want to merge 2 biovec if they are not living on the same MFNs. > As in, is there an SWIOTLB that does PFN to MFN and vice-versa > translation? > > I thought that ARM guests are not exposed to the MFN<->PFN logic > and trying to figure that out to not screw up the DMA engine > on a PCIe device slurping up contingous MFNs which don't map > to contingous PFNs? I will let these 2 questions for Stefano. He knows better than me swiotlb for ARM. So far, I skipped swiotlb implementation for 64KB page granularity as I'm not sure what to do when a page is split across multiple MFNs. Although I don't think this can happen with this specific series as: - The memory is a direct mapping so any Linux page is using contiguous MFNs. - Foreign mapping is using the 4KB of the Linux page. This is for an easier implementation. For the latter, I plan to work on using the Linux page to map multiple foreign gfn. I have to talk with Stefano about it how to handle it. Regards, -- Julien Grall -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/