On Thu, Apr 21, 2016 at 04:43:45PM +0300, Michael S. Tsirkin wrote: > This adds a flag to enable/disable bypassing the IOMMU by > virtio devices. > > This is on top of patch > http://article.gmane.org/gmane.comp.emulators.qemu/403467 > virtio: convert to use DMA api > > Tested with patchset > http://article.gmane.org/gmane.linux.kernel.virtualization/27545 > virtio-pci: iommu support (note: bit number has been kept at 34 > intentionally to match posted guest code. a non-RFC version will > renumber bits to be contigious). > > changes from v1: > drop PASSTHROUGH flag > > The interaction between virtio and DMA API is messy. > > On most systems with virtio, physical addresses match bus addresses, > and it doesn't particularly matter whether we use the DMA API. > > On some systems, including Xen and any system with a physical device > that speaks virtio behind a physical IOMMU, we must use the DMA API > for virtio DMA to work at all. > > Add a feature bit to detect that: VIRTIO_F_IOMMU_PLATFORM. > > If not there, we preserve historic behavior and bypass the DMA > API unless within Xen guest. This is actually required for > systems, including SPARC and PPC64, where virtio-pci devices are > enumerated as though they are behind an IOMMU, but the virtio host > ignores the IOMMU, so we must either pretend that the IOMMU isn't > there or somehow map everything as the identity. > > Re: non-virtio devices. > > It turns out that on old QEMU hosts, only emulated devices which were > part of QEMU use the IOMMU. Should we want to bypass the IOMMU for such > devices *only*, it would be rather easy to detect them by looking at > subsystem vendor and device ID. Thus, no new interfaces are required > except for virtio which always uses the same subsystem vendor and device ID. > > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx> > --- > include/hw/virtio/virtio-access.h | 3 ++- > include/hw/virtio/virtio.h | 4 +++- > include/standard-headers/linux/virtio_config.h | 2 ++ > 3 files changed, 7 insertions(+), 2 deletions(-) > > diff --git a/include/hw/virtio/virtio-access.h b/include/hw/virtio/virtio-access.h > index 967cc75..bb6f34e 100644 > --- a/include/hw/virtio/virtio-access.h > +++ b/include/hw/virtio/virtio-access.h > @@ -23,7 +23,8 @@ static inline AddressSpace *virtio_get_dma_as(VirtIODevice *vdev) > BusState *qbus = qdev_get_parent_bus(DEVICE(vdev)); > VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus); > > - if (k->get_dma_as) { > + if (virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM) && > + k->get_dma_as) { > return k->get_dma_as(qbus->parent); > } > return &address_space_memory; > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h > index b12faa9..44f3788 100644 > --- a/include/hw/virtio/virtio.h > +++ b/include/hw/virtio/virtio.h > @@ -228,7 +228,9 @@ typedef struct VirtIORNGConf VirtIORNGConf; > DEFINE_PROP_BIT64("notify_on_empty", _state, _field, \ > VIRTIO_F_NOTIFY_ON_EMPTY, true), \ > DEFINE_PROP_BIT64("any_layout", _state, _field, \ > - VIRTIO_F_ANY_LAYOUT, true) > + VIRTIO_F_ANY_LAYOUT, true), \ > + DEFINE_PROP_BIT64("iommu_platform", _state, _field, \ > + VIRTIO_F_IOMMU_PLATFORM, false) Looks like the impact of this patch is that users who relied on k->get_dma_as today may now have to explicitly add iommu_platform=on. Are there any such users (e.g. Xen)? Instead of breaking the command-line for these users you could invert the flag's meaning ("iommu_bypass=on") and set it in the SPARC/PPC machine types. Stefan
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