From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH v4 0/4] virtio: Clean up scatterlists and use the DMA API Date: Tue, 28 Jul 2015 10:16:09 +0200 Message-ID: <55B73A49.9050206__6217.75177210129$1438071450$gmane$org@redhat.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Andy Lutomirski , Rusty Russell , "Michael S. Tsirkin" Cc: "linux-s390@vger.kernel.org" , Benjamin Herrenschmidt , Linux Virtualization , Christian Borntraeger , Stefan Hajnoczi , Cornelia Huck , "linux390@de.ibm.com" , xen-devel List-Id: xen-devel@lists.xenproject.org On 28/07/2015 03:08, Andy Lutomirski wrote: > On Mon, Sep 1, 2014 at 10:39 AM, Andy Lutomirski wrote: >> This fixes virtio on Xen guests as well as on any other platform >> that uses virtio_pci on which physical addresses don't match bus >> addresses. >> >> This can be tested with: >> >> virtme-run --xen xen --kimg arch/x86/boot/bzImage --console >> >> using virtme from here: >> >> https://git.kernel.org/cgit/utils/kernel/virtme/virtme.git >> >> Without these patches, the guest hangs forever. With these patches, >> everything works. >> > > Dusting off an ancient thread. > > Now that the dust has accumulated^Wsettled, is it worth pursuing this? > I think the situation is considerably worse than it was when I > originally wrote these patches: I think that QEMU now supports a nasty > mode in which the guest's PCI bus appears to be behind an IOMMU but > the virtio devices on that bus punch straight through that IOMMU. That is an experimental feature (it's x-iommu), so it can change. The plan was: - for PPC, virtio never honors IOMMU - for non-PPC, either have virtio always honor IOMMU, or enforce that virtio is not under IOMMU. Paolo > I have a half-hearted port to modern kernels here: > > https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/log/?h=virtio_ring_xen > > I didn't implement DMA API access for virtio_pci_modern, and I have no > idea what to do about detecting whether a given virtio device honors > its IOMMU or not. > > --Andy >