From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Vrabel Subject: Re: [PATCH v3 0/3] xen/arm: fix "xen_add_mach_to_phys_entry: cannot add" problem Date: Fri, 1 Aug 2014 16:28:49 +0100 Message-ID: <53DBB231.5010900@citrix.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Stefano Stabellini , xen-devel@lists.xensource.com Cc: Julien Grall , v1ne2go@gmail.com, Ian Campbell , linux-arm-kernel@lists.infradead.org List-Id: xen-devel@lists.xenproject.org On 01/08/14 15:55, Stefano Stabellini wrote: > Hi all, > Xen support in Linux for ARM and ARM64 suffers from lack of support for > multiple mfn to pfn mappings: whenever a frontend grants the same page > multiple times to the backend, the mfn to pfn accounting in > arch/arm/xen/p2m.c fails. The issue has become critical since v3.15, > when xen-netfront/xen-netback switched from grant copies to grant > mappings, therefore causing the issue to happen much more often. > > Fixing the mfn to pfn accounting in p2m.c is difficult and expensive, > therefore we are looking for alternative solutions. One idea is avoiding > mfn to pfn conversions altogether. The only code path that needs them is > swiotlb-xen:unmap_page (and single_for_cpu and single_for_device). > > To avoid mfn to pfn conversions we rely on a second p2m mapping done by > Xen (a separate patch series will be sent for Xen). In Linux we use it > to perform the cache maintenance operations without mfns conversions. > > > The Xen side patch series that introduces XENFEAT_grant_map_identity is: > http://marc.info/?l=xen-devel&m=140690433923855 If the Xen side is in master, you can apply this series to devel/for-linus-3.17 David