Add Stefano and Anthony
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 <m...@redhat.com>
> ---
> 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)
>
> hwaddr virtio_queue_get_desc_addr(VirtIODevice *vdev, int n);
> hwaddr virtio_queue_get_avail_addr(VirtIODevice *vdev, int n);
> diff --git a/include/standard-headers/linux/virtio_config.h
> b/include/standard-headers/linux/virtio_config.h
> index bcc445b..3fcfbb1 100644
> --- a/include/standard-headers/linux/virtio_config.h
> +++ b/include/standard-headers/linux/virtio_config.h
> @@ -61,4 +61,6 @@
> /* v1.0 compliant. */
> #define VIRTIO_F_VERSION_1 32
>
> +/* Do not bypass the IOMMU (if configured) */
> +#define VIRTIO_F_IOMMU_PLATFORM 34
> #endif /* _LINUX_VIRTIO_CONFIG_H */
> --
> MST
