Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755490AbbGPSbk (ORCPT ); Thu, 16 Jul 2015 14:31:40 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:46770 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752055AbbGPSbj (ORCPT ); Thu, 16 Jul 2015 14:31:39 -0400 Date: Thu, 16 Jul 2015 14:30:59 -0400 From: Konrad Rzeszutek Wilk To: Julien Grall Cc: Stefano Stabellini , ian.campbell@citrix.com, linux-kernel@vger.kernel.org, David Vrabel , xen-devel@lists.xenproject.org, Boris Ostrovsky , linux-arm-kernel@lists.infradead.org Subject: Re: [Xen-devel] [PATCH v2 09/20] xen/biomerge: Don't allow biovec to be merge when Linux is not using 4KB page Message-ID: <20150716183059.GC14309@x230.dumpdata.com> 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> <55A7D8AD.1090102@citrix.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55A7D8AD.1090102@citrix.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-Source-IP: aserv0022.oracle.com [141.146.126.234] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1680 Lines: 42 On Thu, Jul 16, 2015 at 05:15:41PM +0100, Julien Grall wrote: > Hi Stefano, > > On 16/07/2015 16:33, Stefano Stabellini wrote: > >On Fri, 10 Jul 2015, 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? > >> > >>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? > > > >Dom0 is mapped 1:1, so pfn == mfn normally, however grant maps > >unavoidably screw up the 1:1, so the swiotlb jumps in to save the day > >when a foreign granted page is involved in a dma operation. > > > >Regarding xen_biovec_phys_mergeable, we could check that all the pfn == > >mfn and return true in that case. > > I mentioned it in the commit message. Although, we would have to loop on > every pfn which is slow on 64KB (16 times for every page). Given the biovec > is called often, I don't think we can do a such things. OK - it would be good to have the gist of this email thread in the commit message. Thanks. > > 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/