In preparation to support VIRTIO_F_DMB, read the platform DMA bypass quirk from either feature. The data DMA of a device that negotiates DMB is routed through the IOMMU in front of the region it owns, so the driver has to map every address it publishes through virtio_map_ops. VIRTIO_F_ACCESS_PLATFORM asks a driver for the same thing, and virtio_has_dma_quirk() looks only at it.
virtio_features_ok() demands VIRTIO_F_ACCESS_PLATFORM of a device under restricted memory access, so accept VIRTIO_F_DMB there too. Assisted-by: Kiro:claude-opus-5 checkpatch sparse Signed-off-by: Alexander Graf <[email protected]> --- drivers/virtio/virtio.c | 10 ++++++++-- include/linux/virtio_config.h | 13 ++++++++++++- 2 files changed, 20 insertions(+), 3 deletions(-) diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c index 6f112593566c..3f9d4a3b5930 100644 --- a/drivers/virtio/virtio.c +++ b/drivers/virtio/virtio.c @@ -216,9 +216,15 @@ static int virtio_features_ok(struct virtio_device *dev) return -ENODEV; } - if (!virtio_has_feature(dev, VIRTIO_F_ACCESS_PLATFORM)) { + /* + * VIRTIO_F_ACCESS_PLATFORM and VIRTIO_F_DMB both ensure that + * the device does not access guest memory directly, bypassing + * the platform DMA topology. + */ + if (!virtio_has_feature(dev, VIRTIO_F_ACCESS_PLATFORM) && + !virtio_has_feature(dev, VIRTIO_F_DMB)) { dev_warn(&dev->dev, - "device must provide VIRTIO_F_ACCESS_PLATFORM\n"); + "device must provide VIRTIO_F_ACCESS_PLATFORM or VIRTIO_F_DMB\n"); return -ENODEV; } } diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h index a10d7c27a2aa..a30eb708046a 100644 --- a/include/linux/virtio_config.h +++ b/include/linux/virtio_config.h @@ -273,8 +273,19 @@ static inline bool virtio_has_dma_quirk(const struct virtio_device *vdev) /* * Note the reverse polarity of the quirk feature (compared to most * other features), this is for compatibility with legacy systems. + * + * VIRTIO_F_ACCESS_PLATFORM says that the device is subject to the + * platform DMA topology and the driver maps every address it + * publishes through that topology. The device performs no direct + * guest memory access, so the quirk does not apply. + * + * VIRTIO_F_DMB says that the device holds the virtqueues and the + * buffers they reference in a region it owns, and routes its data + * DMA through the IOMMU in front of that region. The driver maps + * through that IOMMU, so the quirk does not apply either. */ - return !virtio_has_feature(vdev, VIRTIO_F_ACCESS_PLATFORM); + return !(virtio_has_feature(vdev, VIRTIO_F_ACCESS_PLATFORM) || + virtio_has_feature(vdev, VIRTIO_F_DMB)); } static inline
