From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julien Grall Subject: Re: [PATCH v3 0/3] map grant refs at pfn = mfn Date: Fri, 01 Aug 2014 17:21:21 +0100 Message-ID: <53DBBE81.3070902@linaro.org> References: <53DB8A01.5020205@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Thomas Leonard , Stefano Stabellini Cc: Julien Grall , "xen-devel@lists.xensource.com" , Ian Campbell List-Id: xen-devel@lists.xenproject.org On 01/08/14 17:16, Thomas Leonard wrote: > On 1 August 2014 16:13, Stefano Stabellini > wrote: >> On Fri, 1 Aug 2014, Thomas Leonard wrote: >>> On 24/07/14 14:30, Stefano Stabellini wrote: >>>> Hi all, >>>> this patch series introduces a second p2m mapping of grant reference on >>>> ARM at guest physical address == machine address of the grant ref. It >>>> is safe because dom0 is already mapped 1:1. We export >>>> XENFEAT_grant_map_identity to signal the guest that this second p2m >>>> mapping is >>>> available. >>>> >>>> One reason for wanting the second p2m mapping is to avoid tracking mfn >>>> to pfn mappings in the guest kernel. Since the same mfn can be granted >>>> multiple times to the backend, finding the right pfn corresponding to a >>>> given mfn can be difficult and expensive. Providing a second mapping at >>>> a known address allow the kernel to access the page without knowing the >>>> pfn. >>> >>> Is there a version of these patches for Xen 4.4 that I can test? The >>> restriction on duplicate pages is causing trouble for networking on Mirage too >>> (http://roscidus.com/blog/blog/2014/07/28/my-first-unikernel/#tcp-retransmissions). >> >> The backport is non-trivial because >> 552710b388630dfa461932940a998e120c42277d is missing from 4.4, >> nonetheless it wasn't too hard to port: >> >> git://xenbits.xen.org/people/sstabellini/xen-unstable.git grant_map_identity_4.4 > > Thanks. I merged it with the stable-4.4 branch (as that has some > useful fixes too), but it crashed for me when I started my Mirage > guest: You have to drop the BUG_ON line 729. Regards, -- Julien Grall