In preparation to support VIRTIO_F_DMB, define the feature bit. A device that negotiates it holds its virtqueues and the buffers they reference in a Device Memory Buffer, a shared memory region the device owns. Every address the driver publishes to such a device is an offset into that region, so the device can only reach memory the driver placed there.
Define VIRTIO_F_DMB as 44 and raise VIRTIO_TRANSPORT_F_END to 45, so virtio_dev_probe() preserves the bit into finalize_features() where a transport can act on it. VIRTIO_DEVICE_F_MASK derives from the same bound, and the expansion drivers/vdpa/vdpa.c writes out by hand moves with it. The feature is a proposal before the virtio Technical Committee and has no allocated number, so 44 is provisional. Link: https://lore.kernel.org/virtio-comment/[email protected]/ Assisted-by: Kiro:claude-opus-5 checkpatch sparse Signed-off-by: Alexander Graf <[email protected]> --- drivers/vdpa/vdpa.c | 2 +- include/uapi/linux/virtio_config.h | 17 ++++++++++++++++- 2 files changed, 17 insertions(+), 2 deletions(-) diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c index 1757a33f298f..ae9326394c2e 100644 --- a/drivers/vdpa/vdpa.c +++ b/drivers/vdpa/vdpa.c @@ -548,7 +548,7 @@ vdpa_nl_cmd_mgmtdev_get_dumpit(struct sk_buff *msg, struct netlink_callback *cb) /* * Bitmask for all per-device features: feature bits VIRTIO_TRANSPORT_F_START - * through VIRTIO_TRANSPORT_F_END are unset, i.e. 0xfffff8000fffffff for + * through VIRTIO_TRANSPORT_F_END are unset, i.e. 0xffffc0000fffffff for * all 64bit features. If the features are extended beyond 64 bits, or new * "holes" are reserved for other type of features than per-device, this * macro would have to be updated. diff --git a/include/uapi/linux/virtio_config.h b/include/uapi/linux/virtio_config.h index 2445f365bce7..986e2b5fb3c8 100644 --- a/include/uapi/linux/virtio_config.h +++ b/include/uapi/linux/virtio_config.h @@ -52,7 +52,7 @@ * rest are per-device feature bits. */ #define VIRTIO_TRANSPORT_F_START 28 -#define VIRTIO_TRANSPORT_F_END 42 +#define VIRTIO_TRANSPORT_F_END 45 #ifndef VIRTIO_CONFIG_NO_LEGACY /* Do we get callbacks when the ring is completely used, even if we've @@ -120,4 +120,19 @@ */ #define VIRTIO_F_ADMIN_VQ 41 +/* + * This feature indicates that the device offers a Device Memory Buffer: a + * shared memory region, owned by the device, that holds the virtqueues and + * the buffers they reference. When this feature is negotiated, every address + * that the driver places in a virtqueue is an offset into the Device Memory + * Buffer region rather than a physical address or a bus address. The device + * is thereby confined to memory the driver has published in that region. + * + * The feature is a specification proposal before the virtio Technical + * Committee, not a ratified feature. The number below is provisional: the + * committee has allocated none for it, and it will change if the committee + * allocates a different one. Do not treat it as a stable interface yet. + */ +#define VIRTIO_F_DMB 44 + #endif /* _UAPI_LINUX_VIRTIO_CONFIG_H */
