vhost-user: Attempt to fix a race with set_mem_table.
The set_mem_table command currently does not seek a reply. Hence, there is no easy way for a remote application to notify to QEMU when it finished setting up memory, or if there were errors doing so. As an example: (1) Qemu sends a SET_MEM_TABLE to the backend (eg, a vhost-user net application). SET_MEM_TABLE does not require a reply according to the spec. (2) Qemu commits the memory to the guest. (3) Guest issues an I/O operation over a new memory region which was configured on (1). (4) The application has not yet remapped the memory, but it sees the I/O request. (5) The application cannot satisfy the request because it does not know about those GPAs. While a guaranteed fix would require a protocol extension (committed separately), a best-effort workaround for existing applications is to send a GET_FEATURES message before completing the vhost_user_set_mem_table() call. Since GET_FEATURES requires a reply, an application that processes vhost-user messages synchronously would probably have completed the SET_MEM_TABLE before replying. Signed-off-by: Prerna Saxena <prerna.saxena@nutanix.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
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@ -263,66 +263,6 @@ static int vhost_user_set_log_base(struct vhost_dev *dev, uint64_t base,
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return 0;
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}
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static int vhost_user_set_mem_table(struct vhost_dev *dev,
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struct vhost_memory *mem)
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{
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int fds[VHOST_MEMORY_MAX_NREGIONS];
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int i, fd;
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size_t fd_num = 0;
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bool reply_supported = virtio_has_feature(dev->protocol_features,
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VHOST_USER_PROTOCOL_F_REPLY_ACK);
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VhostUserMsg msg = {
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.request = VHOST_USER_SET_MEM_TABLE,
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.flags = VHOST_USER_VERSION,
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};
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if (reply_supported) {
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msg.flags |= VHOST_USER_NEED_REPLY_MASK;
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}
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for (i = 0; i < dev->mem->nregions; ++i) {
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struct vhost_memory_region *reg = dev->mem->regions + i;
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ram_addr_t offset;
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MemoryRegion *mr;
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assert((uintptr_t)reg->userspace_addr == reg->userspace_addr);
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mr = memory_region_from_host((void *)(uintptr_t)reg->userspace_addr,
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&offset);
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fd = memory_region_get_fd(mr);
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if (fd > 0) {
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msg.payload.memory.regions[fd_num].userspace_addr = reg->userspace_addr;
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msg.payload.memory.regions[fd_num].memory_size = reg->memory_size;
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msg.payload.memory.regions[fd_num].guest_phys_addr = reg->guest_phys_addr;
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msg.payload.memory.regions[fd_num].mmap_offset = offset;
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assert(fd_num < VHOST_MEMORY_MAX_NREGIONS);
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fds[fd_num++] = fd;
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}
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}
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msg.payload.memory.nregions = fd_num;
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if (!fd_num) {
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error_report("Failed initializing vhost-user memory map, "
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"consider using -object memory-backend-file share=on");
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return -1;
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}
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msg.size = sizeof(msg.payload.memory.nregions);
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msg.size += sizeof(msg.payload.memory.padding);
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msg.size += fd_num * sizeof(VhostUserMemoryRegion);
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if (vhost_user_write(dev, &msg, fds, fd_num) < 0) {
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return -1;
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}
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if (reply_supported) {
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return process_message_reply(dev, msg.request);
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}
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return 0;
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}
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static int vhost_user_set_vring_addr(struct vhost_dev *dev,
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struct vhost_vring_addr *addr)
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{
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@ -537,6 +477,73 @@ static int vhost_user_get_features(struct vhost_dev *dev, uint64_t *features)
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return vhost_user_get_u64(dev, VHOST_USER_GET_FEATURES, features);
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}
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static int vhost_user_set_mem_table(struct vhost_dev *dev,
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struct vhost_memory *mem)
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{
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int fds[VHOST_MEMORY_MAX_NREGIONS];
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int i, fd;
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size_t fd_num = 0;
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uint64_t features;
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bool reply_supported = virtio_has_feature(dev->protocol_features,
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VHOST_USER_PROTOCOL_F_REPLY_ACK);
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VhostUserMsg msg = {
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.request = VHOST_USER_SET_MEM_TABLE,
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.flags = VHOST_USER_VERSION,
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};
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if (reply_supported) {
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msg.flags |= VHOST_USER_NEED_REPLY_MASK;
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}
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for (i = 0; i < dev->mem->nregions; ++i) {
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struct vhost_memory_region *reg = dev->mem->regions + i;
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ram_addr_t offset;
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MemoryRegion *mr;
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assert((uintptr_t)reg->userspace_addr == reg->userspace_addr);
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mr = memory_region_from_host((void *)(uintptr_t)reg->userspace_addr,
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&offset);
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fd = memory_region_get_fd(mr);
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if (fd > 0) {
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msg.payload.memory.regions[fd_num].userspace_addr
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= reg->userspace_addr;
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msg.payload.memory.regions[fd_num].memory_size = reg->memory_size;
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msg.payload.memory.regions[fd_num].guest_phys_addr
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= reg->guest_phys_addr;
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msg.payload.memory.regions[fd_num].mmap_offset = offset;
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assert(fd_num < VHOST_MEMORY_MAX_NREGIONS);
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fds[fd_num++] = fd;
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}
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}
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msg.payload.memory.nregions = fd_num;
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if (!fd_num) {
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error_report("Failed initializing vhost-user memory map, "
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"consider using -object memory-backend-file share=on");
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return -1;
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}
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msg.size = sizeof(msg.payload.memory.nregions);
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msg.size += sizeof(msg.payload.memory.padding);
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msg.size += fd_num * sizeof(VhostUserMemoryRegion);
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vhost_user_write(dev, &msg, fds, fd_num);
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if (reply_supported) {
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return process_message_reply(dev, msg.request);
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} else {
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/* Note: It is (yet) unknown when the client application has finished
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* remapping the GPA.
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* Attempt to prevent a race by sending a command that requires a reply.
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*/
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vhost_user_get_features(dev, &features);
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}
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return 0;
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}
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static int vhost_user_set_owner(struct vhost_dev *dev)
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{
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VhostUserMsg msg = {
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