vhost: new device IOTLB API

This patch tries to implement an device IOTLB for vhost. This could be
used with userspace(qemu) implementation of DMA remapping
to emulate an IOMMU for the guest.

The idea is simple, cache the translation in a software device IOTLB
(which is implemented as an interval tree) in vhost and use vhost_net
file descriptor for reporting IOTLB miss and IOTLB
update/invalidation. When vhost meets an IOTLB miss, the fault
address, size and access can be read from the file. After userspace
finishes the translation, it writes the translated address to the
vhost_net file to update the device IOTLB.

When device IOTLB is enabled by setting VIRTIO_F_IOMMU_PLATFORM all vq
addresses set by ioctl are treated as iova instead of virtual address and
the accessing can only be done through IOTLB instead of direct userspace
memory access. Before each round or vq processing, all vq metadata is
prefetched in device IOTLB to make sure no translation fault happens
during vq processing.

In most cases, virtqueues are contiguous even in virtual address space.
The IOTLB translation for virtqueue itself may make it a little
slower. We might add fast path cache on top of this patch.

Signed-off-by: Jason Wang <jasowang@redhat.com>
[mst: use virtio feature bit: VHOST_F_DEVICE_IOTLB -> VIRTIO_F_IOMMU_PLATFORM ]
[mst: fix build warnings ]
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
[ weiyj.lk: missing unlock on error ]
Signed-off-by: Wei Yongjun <weiyj.lk@gmail.com>

1 files changed, 28 insertions, 0 deletions

diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
index c4400b267716..56b7ab584cc0 100644
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h
@@ -47,6 +47,32 @@ struct vhost_vring_addr {
 	__u64 log_guest_addr;
 };
 
+/* no alignment requirement */
+struct vhost_iotlb_msg {
+	__u64 iova;
+	__u64 size;
+	__u64 uaddr;
+#define VHOST_ACCESS_RO      0x1
+#define VHOST_ACCESS_WO      0x2
+#define VHOST_ACCESS_RW      0x3
+	__u8 perm;
+#define VHOST_IOTLB_MISS           1
+#define VHOST_IOTLB_UPDATE         2
+#define VHOST_IOTLB_INVALIDATE     3
+#define VHOST_IOTLB_ACCESS_FAIL    4
+	__u8 type;
+};
+
+#define VHOST_IOTLB_MSG 0x1
+
+struct vhost_msg {
+	int type;
+	union {
+		struct vhost_iotlb_msg iotlb;
+		__u8 padding[64];
+	};
+};
+
 struct vhost_memory_region {
 	__u64 guest_phys_addr;
 	__u64 memory_size; /* bytes */
@@ -146,6 +172,8 @@ struct vhost_memory {
 #define VHOST_F_LOG_ALL 26
 /* vhost-net should add virtio_net_hdr for RX, and strip for TX packets. */
 #define VHOST_NET_F_VIRTIO_NET_HDR 27
+/* Vhost have device IOTLB */
+#define VHOST_F_DEVICE_IOTLB 63
 
 /* VHOST_SCSI specific definitions */