From mboxrd@z Thu Jan 1 00:00:00 1970 From: Olaf Hering Subject: Re: Need help with fixing the Xen waitqueue feature Date: Wed, 9 Nov 2011 23:11:49 +0100 Message-ID: <20111109221148.GA17166@aepfle.de> References: <20111108224414.83985CF73A@homiemail-mx7.g.dreamhost.com> <3c097da8e49a42af1210e4ffcd39fd48.squirrel@webmail.lagarcavilla.org> <20111109070927.GB26154@aepfle.de> <0bb01a4d216a68c4ae8441b037927f61.squirrel@webmail.lagarcavilla.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Return-path: Content-Disposition: inline In-Reply-To: <0bb01a4d216a68c4ae8441b037927f61.squirrel@webmail.lagarcavilla.org> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Andres Lagar-Cavilla Cc: keir.xen@gmail.com, xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org On Wed, Nov 09, Andres Lagar-Cavilla wrote: > After a bit of thinking, things are far more complicated. I don't think > this is a "race." If the pager removed a page that later gets scheduled by > the guest OS for IO, qemu will want to foreign-map that. With the > hypervisor returning ENOENT, the foreign map will fail, and there goes > qemu. The tools are supposed to catch ENOENT and try again. linux_privcmd_map_foreign_bulk() does that. linux_gnttab_grant_map() appears to do that as well. What code path uses qemu that leads to a crash? > I guess qemu/migrate/libxc could retry until the pager is done and the > mapping succeeds. It will be delicate. It won't work for pv backends. It > will flood the mem_event ring. There will no flood, only one request is sent per gfn in p2m_mem_paging_populate(). Olaf