From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:52062) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Wnwow-0004co-AL for qemu-devel@nongnu.org; Fri, 23 May 2014 17:16:11 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Wnwor-0004si-C5 for qemu-devel@nongnu.org; Fri, 23 May 2014 17:16:06 -0400 Message-ID: <537FBA8A.6020704@suse.de> Date: Fri, 23 May 2014 23:15:54 +0200 From: Alexander Graf MIME-Version: 1.0 References: <1400821160-25258-1-git-send-email-aik@ozlabs.ru> <1400821160-25258-6-git-send-email-aik@ozlabs.ru> <537F30C7.3010704@suse.de> <537F392B.7020209@ozlabs.ru> <537F3972.9080907@suse.de> <537F7473.6000200@ozlabs.ru> In-Reply-To: <537F7473.6000200@ozlabs.ru> Content-Type: text/plain; charset=KOI8-R; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v6 5/7] vfio: Introduce VFIO address spaces List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alexey Kardashevskiy , qemu-devel@nongnu.org Cc: Alex Williamson , qemu-ppc@nongnu.org, David Gibson On 23.05.14 18:16, Alexey Kardashevskiy wrote: > On 05/23/2014 10:05 PM, Alexander Graf wrote: >> On 23.05.14 14:03, Alexey Kardashevskiy wrote: >>> On 05/23/2014 09:28 PM, Alexander Graf wrote: >>>> On 23.05.14 06:59, Alexey Kardashevskiy wrote: >>>>> From: David Gibson >>>>> >>>>> The only model so far supported for VFIO passthrough devices is the model >>>>> usually used on x86, where all of the guest's RAM is mapped into the >>>>> (host) IOMMU and there is no IOMMU visible in the guest. >>>>> >>>>> This patch begins to relax this model, introducing the notion of a >>>>> VFIOAddressSpace. This represents a logical DMA address space which will >>>>> be visible to one or more VFIO devices by appropriate mapping in the >>>>> (host) >>>>> IOMMU. Thus the currently global list of containers becomes local to >>>>> a VFIOAddressSpace, and we verify that we don't attempt to add a VFIO >>>>> group to multiple address spaces. >>>>> >>>>> For now, only one VFIOAddressSpace is created and used, corresponding to >>>>> main system memory, that will change in future patches. >>>>> >>>>> Signed-off-by: David Gibson >>>>> Signed-off-by: Alexey Kardashevskiy >>>> Don't we already have a DMA address space in the PCI bus? We could just use >>>> that one instead, no? >>> I do not know about x86, but for spapr that VFIOAddressSpace is nothing but >>> wrapper around an AddressSpace from the SPAPR PHB. >> So why do we need that wrapper? Can't we just use the PHB's AddressSpace? >> There's a good chance I'm not grasping something here :). > > We cannot attach VFIO containers (aka "groups" or "PEs" for spapr) to > AddressSpace, there is nothing like that in AddressSpace/MemoryRegion API > as this container thing is local to VFIO. Ok, please explain how this AddressSpace is different from the VFIO device's parent's IOMMU DMA AddressSpace and why we need it. Alex