From mboxrd@z Thu Jan 1 00:00:00 1970 From: Olaf Hering Subject: Re: fixed location of share info page in HVM guests Date: Mon, 27 Aug 2012 23:56:36 +0200 Message-ID: <20120827215636.GA22031@aepfle.de> References: <20120827213226.GA17915@aepfle.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline 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: Keir Fraser Cc: xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org On Mon, Aug 27, Keir Fraser wrote: > On 27/08/2012 22:32, "Olaf Hering" wrote: > > >>> Recently I tried to move the shared_info page in the pvops kernel during > >>> shutdown, see "xen PVonHVM: move shared_info to MMIO before kexec" > >>> patch. But this change was reverted because it caused reboot failures > >>> because the actual moving of the shared page is fragile. > >> > >> How was it fragile? Moving it into MMIO should just work? > > > > The moving itself is not the issue, but the possible access to the page > > during the move. Its not atomic, nor can it easily be atomic. > > Why not map it into MMIO in the first place, rather than into the middle of > RAM? Do that early during boot, and early during resume from > save/restore/migrate (i.e., places you presumably already map the > shared_info page, but into the middle of RAM)? I think there is no easy way to know where the PCI device is located at the time the shared info page is configured in the early kernel setup. Olaf