Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755909AbbGPPel (ORCPT ); Thu, 16 Jul 2015 11:34:41 -0400 Received: from smtp02.citrix.com ([66.165.176.63]:50797 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754796AbbGPPej (ORCPT ); Thu, 16 Jul 2015 11:34:39 -0400 X-IronPort-AV: E=Sophos;i="5.15,488,1432598400"; d="scan'208";a="284766076" Date: Thu, 16 Jul 2015 16:33:19 +0100 From: Stefano Stabellini X-X-Sender: sstabellini@kaball.uk.xensource.com To: Konrad Rzeszutek Wilk CC: Julien Grall , , , , , , "Boris Ostrovsky" , David Vrabel Subject: Re: [PATCH v2 09/20] xen/biomerge: Don't allow biovec to be merge when Linux is not using 4KB page In-Reply-To: <20150710191245.GA31063@l.oracle.com> Message-ID: 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> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" X-DLP: MIA2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2589 Lines: 70 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'm not sure how to handle efficiently the check to know whether we can > > merge 2 biovec with a such case. So for now, always says that biovec are > > not mergeable. > > > > Signed-off-by: Julien Grall > > Cc: Konrad Rzeszutek Wilk > > Cc: Boris Ostrovsky > > Cc: David Vrabel > > --- > > Changes in v2: > > - Remove the workaround and check if the Linux page granularity > > is the same as Xen or not > > --- > > drivers/xen/biomerge.c | 7 +++++++ > > 1 file changed, 7 insertions(+) > > > > diff --git a/drivers/xen/biomerge.c b/drivers/xen/biomerge.c > > index 0edb91c..571567c 100644 > > --- a/drivers/xen/biomerge.c > > +++ b/drivers/xen/biomerge.c > > @@ -6,10 +6,17 @@ > > bool xen_biovec_phys_mergeable(const struct bio_vec *vec1, > > const struct bio_vec *vec2) > > { > > +#if XEN_PAGE_SIZE == PAGE_SIZE > > unsigned long mfn1 = pfn_to_mfn(page_to_pfn(vec1->bv_page)); > > unsigned long mfn2 = pfn_to_mfn(page_to_pfn(vec2->bv_page)); > > > > return __BIOVEC_PHYS_MERGEABLE(vec1, vec2) && > > ((mfn1 == mfn2) || ((mfn1+1) == mfn2)); > > +#else > > + /* XXX: bio_vec are not mergeable when using different page size in > > + * Xen and Linux > > + */ > > + return 0; > > +#endif > > } > > EXPORT_SYMBOL(xen_biovec_phys_mergeable); > > -- > > 2.1.4 > > > -- 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/