From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:44168) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QN7C4-0004ed-Vh for qemu-devel@nongnu.org; Thu, 19 May 2011 13:39:29 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QN7C4-0003F2-3U for qemu-devel@nongnu.org; Thu, 19 May 2011 13:39:28 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48268) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QN7C3-0003Er-Si for qemu-devel@nongnu.org; Thu, 19 May 2011 13:39:28 -0400 Date: Thu, 19 May 2011 20:39:23 +0300 From: Gleb Natapov Message-ID: <20110519173923.GF27310@redhat.com> References: <4DD3C5B9.1080908@redhat.com> <4DD420A5.2020606@web.de> <4DD51CF3.5040306@codemonkey.ws> <4DD51D36.7040504@siemens.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4DD51D36.7040504@siemens.com> Subject: Re: [Qemu-devel] [RFC] Memory API List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jan Kiszka Cc: Avi Kivity , qemu-devel On Thu, May 19, 2011 at 03:37:58PM +0200, Jan Kiszka wrote: > On 2011-05-19 15:36, Anthony Liguori wrote: > > On 05/18/2011 02:40 PM, Jan Kiszka wrote: > >> On 2011-05-18 15:12, Avi Kivity wrote: > >>> void cpu_register_memory_region(MemoryRegion *mr, target_phys_addr_t > >>> addr); > >> > >> OK, let's allow overlapping, but make it explicit: > >> > >> void cpu_register_memory_region_overlap(MemoryRegion *mr, > >> target_phys_addr_t addr, > >> int priority); > > > > The device doesn't actually know how overlapping is handled. This is > > based on the bus hierarchy. > > Devices don't register their regions, buses do. > Today PCI device may register region that overlaps with any other registered memory region without even knowing it. Guest can write any RAM address into PCI BAR and this RAM address will be come mmio are. More interesting is what happens when guest reprogram PCI BAR to other address - the RAM that was at the previous address just disappears. Obviously this is crazy behaviour, but the question is how do we want to handle it? One option is to disallow such overlapping registration, another is to restore RAM mapping after PCI BAR is reprogrammed. If we chose second one the PCI will not know that _overlap() should be called. Another example may be APIC region and PCI. They overlap, but neither CPU nor PCI knows about it. -- Gleb.