From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Jan Beulich" Subject: Re: Ideas for PV on SeaBIOS Date: Thu, 19 May 2011 09:08:37 +0100 Message-ID: <4DD4EC2502000078000420F7@vpn.id2.novell.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: Content-Disposition: inline List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Daniel Castro Cc: xen-devel@lists.xensource.com, seabios@seabios.org List-Id: xen-devel@lists.xenproject.org >>> On 19.05.11 at 07:33, Daniel Castro wrote: > In order to give PV Drivers to SeaBIOS we will need to solve a few > problems, one is the following: > Does a booting kernel informs the BIOS that it will leave real mode > and not use it again? When the booting kernel uses CPU real mode for > the last time, how can we (Xen or SeaBIOS) know that real mode will no > longer be used, and hence BIOS calls will not be issued? > We want upon last real mode usage to leave all Xen PV information in a > clean state, this means, closing the channel and ring between the > newly created domain and the host system. How can you be certain an OS won't switch back to real mode even after an extended period of up-time? Or that such switching back would affect you (could be calling e.g. the video or PCI BIOS functions only). There is INT15 AX=3DEC00 with BX specifying the target operating mode, but that's apparently being called only before entering long mode (i.e. wouldn't cover 32-bit OSes). And it would neither be a guarantee that the OS might not later return to real mode. Jan