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Re: [Qemu-devel] [PATCH v4 2/2] vhost-user: Attempt to fix a race with s
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH v4 2/2] vhost-user: Attempt to fix a race with set_mem_table. |
Date: |
Wed, 27 Jul 2016 16:30:00 +0300 |
On Wed, Jul 27, 2016 at 02:52:37AM -0700, Prerna Saxena wrote:
> From: Prerna Saxena <address@hidden>
>
> 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 <address@hidden>
Could you pls reorder patchset so this is 1/2?
1/1 is still under review but I'd like to make sure
we have some kind of fix in place for 2.7.
> ---
> hw/virtio/vhost-user.c | 123
> ++++++++++++++++++++++++++-----------------------
> 1 file changed, 65 insertions(+), 58 deletions(-)
>
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index 0cdb918..f96607e 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -254,64 +254,6 @@ static int vhost_user_set_log_base(struct vhost_dev
> *dev, uint64_t base,
> return 0;
> }
>
> -static int vhost_user_set_mem_table(struct vhost_dev *dev,
> - struct vhost_memory *mem)
> -{
> - int fds[VHOST_MEMORY_MAX_NREGIONS];
> - int i, fd;
> - size_t fd_num = 0;
> - bool reply_supported = virtio_has_feature(dev->protocol_features,
> - VHOST_USER_PROTOCOL_F_REPLY_ACK);
> -
> - VhostUserMsg msg = {
> - .request = VHOST_USER_SET_MEM_TABLE,
> - .flags = VHOST_USER_VERSION,
> - };
> -
> - if (reply_supported) {
> - msg.flags |= VHOST_USER_NEED_RESPONSE_MASK;
> - }
> -
> - for (i = 0; i < dev->mem->nregions; ++i) {
> - struct vhost_memory_region *reg = dev->mem->regions + i;
> - ram_addr_t offset;
> - MemoryRegion *mr;
> -
> - assert((uintptr_t)reg->userspace_addr == reg->userspace_addr);
> - mr = memory_region_from_host((void *)(uintptr_t)reg->userspace_addr,
> - &offset);
> - fd = memory_region_get_fd(mr);
> - if (fd > 0) {
> - msg.payload.memory.regions[fd_num].userspace_addr =
> reg->userspace_addr;
> - msg.payload.memory.regions[fd_num].memory_size =
> reg->memory_size;
> - msg.payload.memory.regions[fd_num].guest_phys_addr =
> reg->guest_phys_addr;
> - msg.payload.memory.regions[fd_num].mmap_offset = offset;
> - assert(fd_num < VHOST_MEMORY_MAX_NREGIONS);
> - fds[fd_num++] = fd;
> - }
> - }
> -
> - msg.payload.memory.nregions = fd_num;
> -
> - if (!fd_num) {
> - error_report("Failed initializing vhost-user memory map, "
> - "consider using -object memory-backend-file share=on");
> - return -1;
> - }
> -
> - msg.size = sizeof(msg.payload.memory.nregions);
> - msg.size += sizeof(msg.payload.memory.padding);
> - msg.size += fd_num * sizeof(VhostUserMemoryRegion);
> -
> - vhost_user_write(dev, &msg, fds, fd_num);
> -
> - if (reply_supported) {
> - return process_message_reply(dev, msg.request);
> - }
> -
> - return 0;
> -}
> -
> static int vhost_user_set_vring_addr(struct vhost_dev *dev,
> struct vhost_vring_addr *addr)
> {
> @@ -514,6 +456,71 @@ static int vhost_user_get_features(struct vhost_dev
> *dev, uint64_t *features)
> return vhost_user_get_u64(dev, VHOST_USER_GET_FEATURES, features);
> }
>
> +static int vhost_user_set_mem_table(struct vhost_dev *dev,
> + struct vhost_memory *mem)
> +{
> + int fds[VHOST_MEMORY_MAX_NREGIONS];
> + int i, fd;
> + size_t fd_num = 0;
> + uint64_t features;
> + bool reply_supported = virtio_has_feature(dev->protocol_features,
> + VHOST_USER_PROTOCOL_F_REPLY_ACK);
> +
> + VhostUserMsg msg = {
> + .request = VHOST_USER_SET_MEM_TABLE,
> + .flags = VHOST_USER_VERSION,
> + };
> +
> + if (reply_supported) {
> + msg.flags |= VHOST_USER_NEED_RESPONSE_MASK;
> + }
> +
> + for (i = 0; i < dev->mem->nregions; ++i) {
> + struct vhost_memory_region *reg = dev->mem->regions + i;
> + ram_addr_t offset;
> + MemoryRegion *mr;
> +
> + assert((uintptr_t)reg->userspace_addr == reg->userspace_addr);
> + mr = memory_region_from_host((void *)(uintptr_t)reg->userspace_addr,
> + &offset);
> + fd = memory_region_get_fd(mr);
> + if (fd > 0) {
> + msg.payload.memory.regions[fd_num].userspace_addr =
> reg->userspace_addr;
> + msg.payload.memory.regions[fd_num].memory_size =
> reg->memory_size;
> + msg.payload.memory.regions[fd_num].guest_phys_addr =
> reg->guest_phys_addr;
> + msg.payload.memory.regions[fd_num].mmap_offset = offset;
> + assert(fd_num < VHOST_MEMORY_MAX_NREGIONS);
> + fds[fd_num++] = fd;
> + }
> + }
> +
> + msg.payload.memory.nregions = fd_num;
> +
> + if (!fd_num) {
> + error_report("Failed initializing vhost-user memory map, "
> + "consider using -object memory-backend-file share=on");
> + return -1;
> + }
> +
> + msg.size = sizeof(msg.payload.memory.nregions);
> + msg.size += sizeof(msg.payload.memory.padding);
> + msg.size += fd_num * sizeof(VhostUserMemoryRegion);
> +
> + vhost_user_write(dev, &msg, fds, fd_num);
> +
> + if (reply_supported) {
> + return process_message_reply(dev, msg.request);
> + } else {
> + /* Note: It is (yet) unknown when the client application has finished
> + * remapping the GPA.
> + * Attempt to prevent a race by sending a command that requires a
> reply.
> + */
> + vhost_user_get_features(dev, &features);
> + }
> +
> + return 0;
> +}
> +
> static int vhost_user_set_owner(struct vhost_dev *dev)
> {
> VhostUserMsg msg = {
> --
> 1.8.1.2
[Qemu-devel] [PATCH v4 2/2] vhost-user: Attempt to fix a race with set_mem_table., Prerna Saxena, 2016/07/27
- Re: [Qemu-devel] [PATCH v4 2/2] vhost-user: Attempt to fix a race with set_mem_table.,
Michael S. Tsirkin <=