Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161043AbbHGQss (ORCPT ); Fri, 7 Aug 2015 12:48:48 -0400 Received: from smtp02.citrix.com ([66.165.176.63]:50681 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932588AbbHGQsN (ORCPT ); Fri, 7 Aug 2015 12:48:13 -0400 X-IronPort-AV: E=Sophos;i="5.15,630,1432598400"; d="scan'208";a="292474703" From: Julien Grall To: CC: , , , , "Julien Grall" , Konrad Rzeszutek Wilk , Boris Ostrovsky , David Vrabel Subject: [PATCH v3 09/20] xen/biomerge: Don't allow biovec to be merge when Linux is not using 4KB page Date: Fri, 7 Aug 2015 17:46:48 +0100 Message-ID: <1438966019-19322-10-git-send-email-julien.grall@citrix.com> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1438966019-19322-1-git-send-email-julien.grall@citrix.com> References: <1438966019-19322-1-git-send-email-julien.grall@citrix.com> MIME-Version: 1.0 Content-Type: text/plain X-DLP: MIA1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2276 Lines: 70 On ARM all dma-capable devices on a same platform may not be protected by an IOMMU. The DMA requests have to use the BFN (i.e MFN on ARM) in order to use correctly the device. While the DOM0 memory is allocated in a 1:1 fashion (PFN == MFN), grant mapping will screw this contiguous mapping. When Linux is using 64KB page granularitary, the page may be split accross multiple non-contiguous MFN (Xen is using 4KB page granularity). Therefore a DMA request will likely fail. Checking that a 64KB page is using contiguous MFN is tedious. For now, always says that biovec are not mergeable. Signed-off-by: Julien Grall --- Cc: Konrad Rzeszutek Wilk Cc: Boris Ostrovsky Cc: David Vrabel There is some ideas to check whether two biovec could be merged (see [1]) but it's not critical and can be consider as a performance improvement. Changes in v3: - Update commit message - s/mfn/bfn/ base on the new renaming - Update TODO Changes in v2: - Remove the workaround and check if the Linux page granularity is the same as Xen or not [1] https://lkml.org/lkml/2015/7/17/418 --- drivers/xen/biomerge.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/drivers/xen/biomerge.c b/drivers/xen/biomerge.c index 8ae2fc90..4da69db 100644 --- a/drivers/xen/biomerge.c +++ b/drivers/xen/biomerge.c @@ -6,10 +6,18 @@ bool xen_biovec_phys_mergeable(const struct bio_vec *vec1, const struct bio_vec *vec2) { +#if XEN_PAGE_SIZE == PAGE_SIZE unsigned long bfn1 = pfn_to_bfn(page_to_pfn(vec1->bv_page)); unsigned long bfn2 = pfn_to_bfn(page_to_pfn(vec2->bv_page)); return __BIOVEC_PHYS_MERGEABLE(vec1, vec2) && ((bfn1 == bfn2) || ((bfn1+1) == bfn2)); +#else + /* + * XXX: Add support for merging bio_vec 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/