From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:37103) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RLa6m-0001u6-SN for qemu-devel@nongnu.org; Wed, 02 Nov 2011 08:39:57 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RLa6k-0008Mt-9e for qemu-devel@nongnu.org; Wed, 02 Nov 2011 08:39:56 -0400 Received: from e38.co.us.ibm.com ([32.97.110.159]:51778) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RLa6j-0008Ml-W0 for qemu-devel@nongnu.org; Wed, 02 Nov 2011 08:39:54 -0400 Received: from /spool/local by e38.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 2 Nov 2011 06:39:32 -0600 Received: from d03av05.boulder.ibm.com (d03av05.boulder.ibm.com [9.17.195.85]) by d03relay01.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id pA2CdCNf309562 for ; Wed, 2 Nov 2011 06:39:12 -0600 Received: from d03av05.boulder.ibm.com (loopback [127.0.0.1]) by d03av05.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id pA2CdBbv031011 for ; Wed, 2 Nov 2011 06:39:11 -0600 Message-ID: <4EB139ED.7080400@us.ibm.com> Date: Wed, 02 Nov 2011 07:39:09 -0500 From: Anthony Liguori MIME-Version: 1.0 References: <1317360376-12090-1-git-send-email-david@gibson.dropbear.id.au> <4EB07096.4070806@us.ibm.com> <87r51rtdgw.fsf@rustcorp.com.au> In-Reply-To: <87r51rtdgw.fsf@rustcorp.com.au> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] virtio: Add PCI memory BAR in addition to PIO BAR List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Rusty Russell Cc: Alexey Kardashevskiy , "Michael S. Tsirkin" , qemu-devel@nongnu.org, Sasha Levin , David Gibson On 11/01/2011 10:22 PM, Rusty Russell wrote: > On Tue, 01 Nov 2011 17:20:06 -0500, Anthony Liguori wrote: >> On 09/30/2011 12:26 AM, David Gibson wrote: >>> Currently, virtio devices are usually presented to the guest as an >>> emulated PCI device, virtio_pci. Although the actual IO operations >>> are done through system memory, the configuration of the virtio device >>> is done through the one PCI IO space BAR that virtio_pci presents. >>> >>> But PCI IO space (aka PIO) is deprecated for modern PCI devices, and >>> on some systems with many PCI domains accessing PIO space can be >>> problematic. For example on the existing PowerVM implementation of >>> the PAPR spec, PCI PIO access is not supported at all. We're hoping >>> that our KVM implementation will support PCI PIO (once we support PCI >>> at all), but it will probably have some irritating limitations. >>> >>> This patch, therefore, extends the virtio_pci device to have a PCI >>> memory space (MMIO) BAR as well as the IO BAR. The MMIO BAR contains >>> exactly the same registers, in exactly the same layout as the existing >>> PIO BAR. >>> >>> Because the PIO BAR is still present, existing guest drivers should >>> still work fine. With this change in place, future guest drivers can >>> check for an MMIO BAR and use that if present (falling back to PIO >>> when possible to support older qemu versions). >>> >>> Signed-off-by: David Gibson >> >> Seems harmless for QEMU, so applied. You should update the virtio-pci spec too. >> >> Regards, > > Can you revert this? We just reverted the kernel part, figuring we need > a rethink. Already did. Regards, Anthony Liguori > > Thanks, > Rusty. >