From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:41788) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RDuPt-0007hu-H0 for qemu-devel@nongnu.org; Wed, 12 Oct 2011 04:43:58 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RDuPp-00032p-1K for qemu-devel@nongnu.org; Wed, 12 Oct 2011 04:43:57 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48993) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RDuPo-00032g-Ol for qemu-devel@nongnu.org; Wed, 12 Oct 2011 04:43:53 -0400 Date: Wed, 12 Oct 2011 10:44:38 +0200 From: "Michael S. Tsirkin" Message-ID: <20111012084437.GC7514@redhat.com> References: <1315197304-22469-1-git-send-email-david@gibson.dropbear.id.au> <1315197304-22469-2-git-send-email-david@gibson.dropbear.id.au> <20111002102547.GC30747@redhat.com> <4E883CF4.6060606@redhat.com> <20111002105238.GE30747@redhat.com> <20111012031137.GQ4849@truffala.fritz.box> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111012031137.GQ4849@truffala.fritz.box> Subject: Re: [Qemu-devel] [PATCH 1/9] Add stub functions for PCI device models to do PCI DMA List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Avi Kivity , qemu-devel@nongnu.org, joerg.roedel@amd.com, aliguori@us.ibm.com, rth@twiddle.net, agraf@suse.de, eduard.munteanu@linux360.ro, kraxel@redhat.com On Wed, Oct 12, 2011 at 02:11:37PM +1100, David Gibson wrote: > On Sun, Oct 02, 2011 at 12:52:39PM +0200, Michael S. Tsirkin wrote: > > On Sun, Oct 02, 2011 at 12:29:08PM +0200, Avi Kivity wrote: > > > On 10/02/2011 12:25 PM, Michael S. Tsirkin wrote: > > > >On Mon, Sep 05, 2011 at 02:34:56PM +1000, David Gibson wrote: > > > >> This patch adds functions to pci.[ch] to perform PCI DMA operations. At > > > >> present, these are just stubs which perform directly cpu physical memory > > > >> accesses. > > > >> > > > >> Using these stubs, however, distinguishes PCI device DMA transactions from > > > >> other accesses to physical memory, which will allow PCI IOMMU support to > > > >> be added in one place, rather than updating every PCI driver at that time. > > > >> > > > >> That is, it allows us to update individual PCI drivers to support an IOMMU > > > >> without having yet determined the details of how the IOMMU emulation will > > > >> operate. This will let us remove the most bitrot-sensitive part of an > > > >> IOMMU patch in advance. > > > >> > > > >> Signed-off-by: David Gibson > > > > > > > >So something I just thought about: > > > > > > > >all wrappers now go through cpu_physical_memory_rw. > > > >This is a problem as e.g. virtio assumes that > > > >accesses such as stw are atomic. cpu_physical_memory_rw > > > >is a memcpy which makes no such guarantees. > > > > > > > > > > Let's change cpu_physical_memory_rw() to provide that guarantee for > > > aligned two and four byte accesses. Having separate paths just for > > > that is not maintainable. > > > > Well, we also have stX_phys convert to target native endian-ness > > (nop for KVM but not necessarily for qemu). > > Yes.. as do the stX_pci_dma() helpers. They assume LE, rather than > having two variants, because PCI is an LE spec, and all normal PCI > devices work in LE. IMO, not really. PCI devices do DMA any way they like. LE is probably more common because both ARM and x86 processors are LE. > If we need to model some perverse BE PCI device, > it can reswap itself. An explicit API for this would be cleaner. -- MST