Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754724AbbGJTNS (ORCPT ); Fri, 10 Jul 2015 15:13:18 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:42972 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754519AbbGJTNQ (ORCPT ); Fri, 10 Jul 2015 15:13:16 -0400 Date: Fri, 10 Jul 2015 15:12:45 -0400 From: Konrad Rzeszutek Wilk To: Julien Grall Cc: xen-devel@lists.xenproject.org, linux-arm-kernel@lists.infradead.org, ian.campbell@citrix.com, stefano.stabellini@eu.citrix.com, linux-kernel@vger.kernel.org, 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 Message-ID: <20150710191245.GA31063@l.oracle.com> References: <1436474552-31789-1-git-send-email-julien.grall@citrix.com> <1436474552-31789-10-git-send-email-julien.grall@citrix.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1436474552-31789-10-git-send-email-julien.grall@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: 2129 Lines: 61 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? > > 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/