On Sep 19, 2014 2:33 PM, "Benjamin Herrenschmidt" <benh@xxxxxxxxxxxxxxxxxxx> wrote: > > On Wed, 2014-09-17 at 09:07 -0700, Andy Lutomirski wrote: > > It shouldn't. That being said, at some point this problem will need > > solving on PPC, and this patch doesn't help much, other than adding > > the virtio_ring piece. > > > > I'd really like to see the generic or arch IOMMU code handle this so > > that the PPC special case in the virtio-pci driver can go away. > > > > Another reason that this kind of special casing doesn't belong in > > virtio-pci: if anyone ever binds vfio to a virtio-pci device, if the > > DMA API doesn't work right, then the kernel will go boom or be > > compromised. > > Well, that's also for these reasons that I think your patch shouldn't go > through those virtio_* variants that test that "use_dma_api" flag or > whatever you called it last time I looked :-) > > You should just unconditionally call the DMA API and we should fixup the > special cases by overriding the hooks. Unconditionally for virtio-pci or unconditionally for all drivers? I wouldn't be surprised if some of the virtio-mmio archs have trouble, too. Aarch64, at least, seems to be okay with using the DMA API on virtio_mmio devices, even with IOMMU support compiled in. Are there other relevant architectures that are easy to test? > > I can help you do the override hack for PPC for now, until we can do > something saner accross all architectures. Sure. The question is: should the patches go in to 3.18 as is our should they wait? It would be straightforward to remove the use_dma_api switch PPC, s390, and virtio_mmio are ready. --Andy > > The main problem is s390 but I had a quick chat with Utz Bacher earlier > this week and he seemed to think having s390 use the DMA API shouldn't > be a big deal, they can also hookup some transparent set of ops if > necessary. > > Cheers, > Ben. > > _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
