RE: [PATCH 3/3] vhost_user: support for memory regions

["Bathija, Pravin" <Pravin.Bathija@dell.com>]

Dear Maxime,

I have made the changes as you suggested and also have some queries inline as per your comments.


Internal Use - Confidential
> -----Original Message-----
> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> Sent: Friday, August 29, 2025 5:00 AM
> To: Bathija, Pravin <Pravin.Bathija@dell.com>; dev@dpdk.org
> Cc: pravin.m.bathija.dev@gmail.com
> Subject: Re: [PATCH 3/3] vhost_user: support for memory regions
>
>
> [EXTERNAL EMAIL]
>
> The title is not consistent with other commits in this library.
>
> On 8/12/25 4:33 AM, Pravin M Bathija wrote:
> > - modify data structures and add functions to support
> >    add and remove memory regions/slots
> > - define VHOST_MEMORY_MAX_NREGIONS & modify function
> >    vhost_user_set_mem_table accordingly
> > - dynamically add new memory slots via vhost_user_add_mem_reg
> > - remove unused memory slots via vhost_user_rem_mem_reg
> > - define data structure VhostUserSingleMemReg for single
> >    memory region
> > - modify data structures VhostUserRequest & VhostUserMsg
> >
>
> Please write full sentences, explaining the purpose of this change and not just
> listing the changes themselves.
Done the best I can in the new patch-set I just submitted.

>
> > Signed-off-by: Pravin M Bathija <pravin.bathija@dell.com>
> > ---
> >   lib/vhost/vhost_user.c | 325 +++++++++++++++++++++++++++++++++++---
> ---
> >   lib/vhost/vhost_user.h |  10 ++
> >   2 files changed, 291 insertions(+), 44 deletions(-)
> >
> > diff --git a/lib/vhost/vhost_user.c b/lib/vhost/vhost_user.c index
> > b73dec6a22..6367f54b97 100644
> > --- a/lib/vhost/vhost_user.c
> > +++ b/lib/vhost/vhost_user.c
> > @@ -74,6 +74,9 @@
> VHOST_MESSAGE_HANDLER(VHOST_USER_SET_FEATURES,
> vhost_user_set_features, false, t
> >   VHOST_MESSAGE_HANDLER(VHOST_USER_SET_OWNER,
> vhost_user_set_owner, false, true) \
> >   VHOST_MESSAGE_HANDLER(VHOST_USER_RESET_OWNER,
> vhost_user_reset_owner, false, false) \
> >   VHOST_MESSAGE_HANDLER(VHOST_USER_SET_MEM_TABLE,
> > vhost_user_set_mem_table, true, true) \
> > +VHOST_MESSAGE_HANDLER(VHOST_USER_GET_MAX_MEM_SLOTS,
> > +vhost_user_get_max_mem_slots, false, false) \
> > +VHOST_MESSAGE_HANDLER(VHOST_USER_ADD_MEM_REG,
> vhost_user_add_mem_reg,
> > +true, true) \ VHOST_MESSAGE_HANDLER(VHOST_USER_REM_MEM_REG,
> > +vhost_user_rem_mem_reg, true, true) \
>
> Shouldn't it be:
> VHOST_MESSAGE_HANDLER(VHOST_USER_REM_MEM_REG,
> vhost_user_rem_mem_reg, false, true)
>
> And if not, aren't you not leaking FDs in vhost_user_rem_mem_reg?
>
Good catch. I have made the suggested change in the new patch-set.

> >   VHOST_MESSAGE_HANDLER(VHOST_USER_SET_LOG_BASE,
> vhost_user_set_log_base, true, true) \
> >   VHOST_MESSAGE_HANDLER(VHOST_USER_SET_LOG_FD,
> vhost_user_set_log_fd, true, true) \
> >   VHOST_MESSAGE_HANDLER(VHOST_USER_SET_VRING_NUM,
> > vhost_user_set_vring_num, false, true) \ @@ -228,7 +231,17 @@
> async_dma_map(struct virtio_net *dev, bool do_map)
> >   }
> >
> >   static void
> > -free_mem_region(struct virtio_net *dev)
> > +free_mem_region(struct rte_vhost_mem_region *reg) {
> > +   if (reg != NULL && reg->host_user_addr) {
> > +           munmap(reg->mmap_addr, reg->mmap_size);
> > +           close(reg->fd);
> > +           memset(reg, 0, sizeof(struct rte_vhost_mem_region));
> > +   }
> > +}
> > +
> > +static void
> > +free_all_mem_regions(struct virtio_net *dev)
> >   {
> >     uint32_t i;
> >     struct rte_vhost_mem_region *reg;
> > @@ -239,12 +252,10 @@ free_mem_region(struct virtio_net *dev)
> >     if (dev->async_copy && rte_vfio_is_enabled("vfio"))
> >             async_dma_map(dev, false);
> >
> > -   for (i = 0; i < dev->mem->nregions; i++) {
> > +   for (i = 0; i < VHOST_MEMORY_MAX_NREGIONS; i++) {
> >             reg = &dev->mem->regions[i];
> > -           if (reg->host_user_addr) {
> > -                   munmap(reg->mmap_addr, reg->mmap_size);
> > -                   close(reg->fd);
> > -           }
> > +           if (reg->mmap_addr)
> > +                   free_mem_region(reg);
>
> Please split this patch in multiple ones.
> Do the refactorings in dedicated patches.

I have split the original patch into multiple patches.

>
> >     }
> >   }
> >
> > @@ -258,7 +269,7 @@ vhost_backend_cleanup(struct virtio_net *dev)
> >             vdpa_dev->ops->dev_cleanup(dev->vid);
> >
> >     if (dev->mem) {
> > -           free_mem_region(dev);
> > +           free_all_mem_regions(dev);
> >             rte_free(dev->mem);
> >             dev->mem = NULL;
> >     }
> > @@ -707,7 +718,7 @@ numa_realloc(struct virtio_net **pdev, struct
> vhost_virtqueue **pvq)
> >     vhost_devices[dev->vid] = dev;
> >
> >     mem_size = sizeof(struct rte_vhost_memory) +
> > -           sizeof(struct rte_vhost_mem_region) * dev->mem->nregions;
> > +           sizeof(struct rte_vhost_mem_region) *
> VHOST_MEMORY_MAX_NREGIONS;
> >     mem = rte_realloc_socket(dev->mem, mem_size, 0, node);
> >     if (!mem) {
> >             VHOST_CONFIG_LOG(dev->ifname, ERR, @@ -811,8 +822,10
> @@
> > hua_to_alignment(struct rte_vhost_memory *mem, void *ptr)
> >     uint32_t i;
> >     uintptr_t hua = (uintptr_t)ptr;
> >
> > -   for (i = 0; i < mem->nregions; i++) {
> > +   for (i = 0; i < VHOST_MEMORY_MAX_NREGIONS; i++) {
> >             r = &mem->regions[i];
> > +           if (r->host_user_addr == 0)
> > +                   continue;
> >             if (hua >= r->host_user_addr &&
> >                     hua < r->host_user_addr + r->size) {
> >                     return get_blk_size(r->fd);
> > @@ -1250,9 +1263,13 @@ vhost_user_postcopy_register(struct virtio_net
> *dev, int main_fd,
> >      * retrieve the region offset when handling userfaults.
> >      */
> >     memory = &ctx->msg.payload.memory;
> > -   for (i = 0; i < memory->nregions; i++) {
> > +   for (i = 0; i < VHOST_MEMORY_MAX_NREGIONS; i++) {
> > +           int reg_msg_index = 0;
> >             reg = &dev->mem->regions[i];
> > -           memory->regions[i].userspace_addr = reg->host_user_addr;
> > +           if (reg->host_user_addr == 0)
> > +                   continue;
> > +           memory->regions[reg_msg_index].userspace_addr = reg-
> >host_user_addr;
> > +           reg_msg_index++;
> >     }
> >
> >     /* Send the addresses back to qemu */ @@ -1279,8 +1296,10 @@
> > vhost_user_postcopy_register(struct virtio_net *dev, int main_fd,
> >     }
> >
> >     /* Now userfault register and we can use the memory */
> > -   for (i = 0; i < memory->nregions; i++) {
> > +   for (i = 0; i < VHOST_MEMORY_MAX_NREGIONS; i++) {
> >             reg = &dev->mem->regions[i];
> > +           if (reg->host_user_addr == 0)
> > +                   continue;
> >             if (vhost_user_postcopy_region_register(dev, reg) < 0)
> >                     return -1;
> >     }
> > @@ -1385,6 +1404,46 @@ vhost_user_mmap_region(struct virtio_net *dev,
> >     return 0;
> >   }
> >
> > +static int
> > +vhost_user_initialize_memory(struct virtio_net **pdev) {
> > +   struct virtio_net *dev = *pdev;
> > +   int numa_node = SOCKET_ID_ANY;
> > +
> > +   /*
> > +    * If VQ 0 has already been allocated, try to allocate on the same
> > +    * NUMA node. It can be reallocated later in numa_realloc().
> > +    */
> > +   if (dev->nr_vring > 0)
> > +           numa_node = dev->virtqueue[0]->numa_node;
> > +
> > +   dev->nr_guest_pages = 0;
> > +   if (dev->guest_pages == NULL) {
> > +           dev->max_guest_pages = 8;
> > +           dev->guest_pages = rte_zmalloc_socket(NULL,
> > +                                   dev->max_guest_pages *
> > +                                   sizeof(struct guest_page),
> > +                                   RTE_CACHE_LINE_SIZE,
> > +                                   numa_node);
> > +           if (dev->guest_pages == NULL) {
> > +                   VHOST_CONFIG_LOG(dev->ifname, ERR,
> > +                           "failed to allocate memory for dev-
> >guest_pages");
> > +                   return -1;
> > +           }
> > +   }
> > +
> > +   dev->mem = rte_zmalloc_socket("vhost-mem-table", sizeof(struct
> rte_vhost_memory) +
> > +           sizeof(struct rte_vhost_mem_region) *
> VHOST_MEMORY_MAX_NREGIONS, 0, numa_node);
> > +   if (dev->mem == NULL) {
> > +           VHOST_CONFIG_LOG(dev->ifname, ERR, "failed to allocate
> memory for dev->mem");
> > +           rte_free(dev->guest_pages);
> > +           dev->guest_pages = NULL;
> > +           return -1;
> > +   }
> > +
> > +   return 0;
> > +}
> > +
> >   static int
> >   vhost_user_set_mem_table(struct virtio_net **pdev,
> >                     struct vhu_msg_context *ctx,
> > @@ -1393,7 +1452,6 @@ vhost_user_set_mem_table(struct virtio_net
> **pdev,
> >     struct virtio_net *dev = *pdev;
> >     struct VhostUserMemory *memory = &ctx->msg.payload.memory;
> >     struct rte_vhost_mem_region *reg;
> > -   int numa_node = SOCKET_ID_ANY;
> >     uint64_t mmap_offset;
> >     uint32_t i;
> >     bool async_notify = false;
> > @@ -1438,39 +1496,13 @@ vhost_user_set_mem_table(struct virtio_net
> **pdev,
> >             if (dev->features & (1ULL << VIRTIO_F_IOMMU_PLATFORM))
> >                     vhost_user_iotlb_flush_all(dev);
> >
> > -           free_mem_region(dev);
> > +           free_all_mem_regions(dev);
> >             rte_free(dev->mem);
> >             dev->mem = NULL;
> >     }
> >
> > -   /*
> > -    * If VQ 0 has already been allocated, try to allocate on the same
> > -    * NUMA node. It can be reallocated later in numa_realloc().
> > -    */
> > -   if (dev->nr_vring > 0)
> > -           numa_node = dev->virtqueue[0]->numa_node;
> > -
> > -   dev->nr_guest_pages = 0;
> > -   if (dev->guest_pages == NULL) {
> > -           dev->max_guest_pages = 8;
> > -           dev->guest_pages = rte_zmalloc_socket(NULL,
> > -                                   dev->max_guest_pages *
> > -                                   sizeof(struct guest_page),
> > -                                   RTE_CACHE_LINE_SIZE,
> > -                                   numa_node);
> > -           if (dev->guest_pages == NULL) {
> > -                   VHOST_CONFIG_LOG(dev->ifname, ERR,
> > -                           "failed to allocate memory for dev-
> >guest_pages");
> > -                   goto close_msg_fds;
> > -           }
> > -   }
> > -
> > -   dev->mem = rte_zmalloc_socket("vhost-mem-table", sizeof(struct
> rte_vhost_memory) +
> > -           sizeof(struct rte_vhost_mem_region) * memory->nregions, 0,
> numa_node);
> > -   if (dev->mem == NULL) {
> > -           VHOST_CONFIG_LOG(dev->ifname, ERR, "failed to allocate
> memory for dev->mem");
> > -           goto free_guest_pages;
> > -   }
> > +   if (vhost_user_initialize_memory(pdev) < 0)
> > +           goto close_msg_fds;
>
> This part should be refactored into a dedicated preliminary patch.
The original patch has been divided into multiple patches.
>
> >
> >     for (i = 0; i < memory->nregions; i++) {
> >             reg = &dev->mem->regions[i];
> > @@ -1534,11 +1566,182 @@ vhost_user_set_mem_table(struct virtio_net
> **pdev,
> >     return RTE_VHOST_MSG_RESULT_OK;
> >
> >   free_mem_table:
> > -   free_mem_region(dev);
> > +   free_all_mem_regions(dev);
> >     rte_free(dev->mem);
> >     dev->mem = NULL;
> > +   rte_free(dev->guest_pages);
> > +   dev->guest_pages = NULL;
> > +close_msg_fds:
> > +   close_msg_fds(ctx);
> > +   return RTE_VHOST_MSG_RESULT_ERR;
> > +}
> > +
> > +
> > +static int
> > +vhost_user_get_max_mem_slots(struct virtio_net **pdev __rte_unused,
> > +                   struct vhu_msg_context *ctx,
> > +                   int main_fd __rte_unused)
> > +{
> > +   uint32_t max_mem_slots = VHOST_MEMORY_MAX_NREGIONS;
>
> This VHOST_MEMORY_MAX_NREGIONS value was hardcoded when only
> VHOST_USER_SET_MEM_TABLE was introduced.
>
> With this new features, my understanding is that we can get rid off this limit,
> right?
>
> The good news is increasing it should not break the DPDK ABI.
>
> Would it make sense to increase it?
I have increased the VHOST_MEMORY_MAX_NREGIONS to 128 and tested with qemu, talking to vhost testpmd and adding/removing 128 memory regions.

> > +
> > +   ctx->msg.payload.u64 = (uint64_t)max_mem_slots;
> > +   ctx->msg.size = sizeof(ctx->msg.payload.u64);
> > +   ctx->fd_num = 0;
> >
> > -free_guest_pages:
> > +   return RTE_VHOST_MSG_RESULT_REPLY;
> > +}
> > +
> > +static int
> > +vhost_user_add_mem_reg(struct virtio_net **pdev,
> > +                   struct vhu_msg_context *ctx,
> > +                   int main_fd __rte_unused)
> > +{
> > +   struct virtio_net *dev = *pdev;
> > +   struct VhostUserMemoryRegion *region = &ctx-
> >msg.payload.memory_single.region;
> > +   uint32_t i;
> > +
> > +   /* make sure new region will fit */
> > +   if (dev->mem != NULL && dev->mem->nregions >=
> VHOST_MEMORY_MAX_NREGIONS) {
> > +           VHOST_CONFIG_LOG(dev->ifname, ERR,
> > +                   "too many memory regions already (%u)",
> > +                   dev->mem->nregions);
> > +           goto close_msg_fds;
> > +   }
> > +
> > +   /* make sure supplied memory fd present */
> > +   if (ctx->fd_num != 1) {
> > +           VHOST_CONFIG_LOG(dev->ifname, ERR,
> > +                   "fd count makes no sense (%u)",
> > +                   ctx->fd_num);
> > +           goto close_msg_fds;
> > +   }
>
> There is a lack of support for vDPA devices.
> My understanding here is that the vDPA device does not get the new table
> entry.
>
> In set_mem_table, we call its close callback, but that might be a bit too much
> for simple memory hotplug. we might need another mechanism.
Could you please suggest the other mechanism ?

>
> > +
> > +   /* Make sure no overlap in guest virtual address space */
> > +   if (dev->mem != NULL && dev->mem->nregions > 0) {
> > +           for (uint32_t i = 0; i < VHOST_MEMORY_MAX_NREGIONS; i++)
> {
> > +                   struct rte_vhost_mem_region *current_region =
> > +&dev->mem->regions[i];
> > +
> > +                   if (current_region->mmap_size == 0)
> > +                           continue;
> > +
> > +                   uint64_t current_region_guest_start = current_region-
> >guest_user_addr;
> > +                   uint64_t current_region_guest_end =
> current_region_guest_start
> > +                                                           +
> current_region->mmap_size - 1;
>
> Shouldn't it use size instead of mmap_size to check for overlaps?
>
> > +                   uint64_t proposed_region_guest_start = region-
> >userspace_addr;
> > +                   uint64_t proposed_region_guest_end =
> proposed_region_guest_start
> > +                                                           + region-
> >memory_size - 1;
> > +                   bool overlap = false;
> > +
> > +                   bool current_region_guest_start_overlap =
> > +                           current_region_guest_start >=
> proposed_region_guest_start
> > +                           && current_region_guest_start <=
> proposed_region_guest_end;
> > +                   bool current_region_guest_end_overlap =
> > +                           current_region_guest_end >=
> proposed_region_guest_start
> > +                           && current_region_guest_end <=
> proposed_region_guest_end;
> > +                   bool proposed_region_guest_start_overlap =
> > +                           proposed_region_guest_start >=
> current_region_guest_start
> > +                           && proposed_region_guest_start <=
> current_region_guest_end;
> > +                   bool proposed_region_guest_end_overlap =
> > +                           proposed_region_guest_end >=
> current_region_guest_start
> > +                           && proposed_region_guest_end <=
> current_region_guest_end;
> > +
> > +                   overlap = current_region_guest_start_overlap
> > +                           || current_region_guest_end_overlap
> > +                           || proposed_region_guest_start_overlap
> > +                           || proposed_region_guest_end_overlap;
> > +
> > +                   if (overlap) {
> > +                           VHOST_CONFIG_LOG(dev->ifname, ERR,
> > +                                   "requested memory region overlaps
> with another region");
> > +                           VHOST_CONFIG_LOG(dev->ifname, ERR,
> > +                                   "\tRequested region address:0x%"
> PRIx64,
> > +                                   region->userspace_addr);
> > +                           VHOST_CONFIG_LOG(dev->ifname, ERR,
> > +                                   "\tRequested region size:0x%" PRIx64,
> > +                                   region->memory_size);
> > +                           VHOST_CONFIG_LOG(dev->ifname, ERR,
> > +                                   "\tOverlapping region address:0x%"
> PRIx64,
> > +                                   current_region->guest_user_addr);
> > +                           VHOST_CONFIG_LOG(dev->ifname, ERR,
> > +                                   "\tOverlapping region size:0x%"
> PRIx64,
> > +                                   current_region->mmap_size);
> > +                           goto close_msg_fds;
> > +                   }
> > +
> > +           }
> > +   }
> > +
> > +   /* convert first region add to normal memory table set */
> > +   if (dev->mem == NULL) {
> > +           if (vhost_user_initialize_memory(pdev) < 0)
> > +                   goto close_msg_fds;
> > +   }
> > +
> > +   /* find a new region and set it like memory table set does */
> > +   struct rte_vhost_mem_region *reg = NULL;
> > +   uint64_t mmap_offset;
> > +
> > +   for (uint32_t i = 0; i < VHOST_MEMORY_MAX_NREGIONS; i++) {
> > +           if (dev->mem->regions[i].guest_user_addr == 0) {
> > +                   reg = &dev->mem->regions[i];
> > +                   break;
> > +           }
> > +   }
> > +   if (reg == NULL) {
> > +           VHOST_CONFIG_LOG(dev->ifname, ERR, "no free memory
> region");
> > +           goto close_msg_fds;
> > +   }
> > +
> > +   reg->guest_phys_addr = region->guest_phys_addr;
> > +   reg->guest_user_addr = region->userspace_addr;
> > +   reg->size            = region->memory_size;
> > +   reg->fd              = ctx->fds[0];
> > +
> > +   mmap_offset = region->mmap_offset;
> > +
> > +   if (vhost_user_mmap_region(dev, reg, mmap_offset) < 0) {
> > +           VHOST_CONFIG_LOG(dev->ifname, ERR, "failed to mmap
> region");
> > +           goto close_msg_fds;
> > +   }
> > +
> > +   dev->mem->nregions++;
> > +
> > +   if (dev->async_copy && rte_vfio_is_enabled("vfio"))
> > +           async_dma_map(dev, true);
> > +
> > +   if (vhost_user_postcopy_register(dev, main_fd, ctx) < 0)
> > +           goto free_mem_table;
> > +
> > +   for (i = 0; i < dev->nr_vring; i++) {
> > +           struct vhost_virtqueue *vq = dev->virtqueue[i];
> > +
> > +           if (!vq)
> > +                   continue;
> > +
> > +           if (vq->desc || vq->avail || vq->used) {
> > +                   /* vhost_user_lock_all_queue_pairs locked all qps */
> > +                   VHOST_USER_ASSERT_LOCK(dev, vq,
> VHOST_USER_SET_MEM_TABLE);
>
> VHOST_USER_ASSERT_LOCK(dev, vq, VHOST_USER_ADD_MEM_REG); ?
>
> > +
> > +                   /*
> > +                    * If the memory table got updated, the ring addresses
> > +                    * need to be translated again as virtual addresses have
> > +                    * changed.
> > +                    */
> > +                   vring_invalidate(dev, vq);
> > +
> > +                   translate_ring_addresses(&dev, &vq);
> > +                   *pdev = dev;
> > +           }
> > +   }
> > +
> > +   dump_guest_pages(dev);
> > +
> > +   return RTE_VHOST_MSG_RESULT_OK;
> > +
> > +free_mem_table:
> > +   free_all_mem_regions(dev);
> > +   rte_free(dev->mem);
> > +   dev->mem = NULL;
> >     rte_free(dev->guest_pages);
> >     dev->guest_pages = NULL;
> >   close_msg_fds:
> > @@ -1546,6 +1749,40 @@ vhost_user_set_mem_table(struct virtio_net
> **pdev,
> >     return RTE_VHOST_MSG_RESULT_ERR;
> >   }
> >
> > +static int
> > +vhost_user_rem_mem_reg(struct virtio_net **pdev __rte_unused,
> > +                   struct vhu_msg_context *ctx __rte_unused,
> > +                   int main_fd __rte_unused)
> > +{
> > +   struct virtio_net *dev = *pdev;
> > +   struct VhostUserMemoryRegion *region =
> > +&ctx->msg.payload.memory_single.region;
> > +
>
> It lacks support for vDPA devices.
> In set_mem_table, we call the vDPA close cb to ensure it is not actively
> accessing memoring being unmapped.
>
> We need something similar here, otherwise the vDPA device is not aware of the
> memory being unplugged.

I have incorporated this change in the latest patch-set.

>
> > +   if (dev->mem != NULL && dev->mem->nregions > 0) {
> > +           for (uint32_t i = 0; i < VHOST_MEMORY_MAX_NREGIONS; i++)
> {
> > +                   struct rte_vhost_mem_region *current_region =
> > +&dev->mem->regions[i];
> > +
> > +                   if (current_region->guest_user_addr == 0)
> > +                           continue;
> > +
> > +                   /*
> > +                    * According to the vhost-user specification:
> > +                    * The memory region to be removed is identified by
> its guest address,
> > +                    * user address and size. The mmap offset is ignored.
> > +                    */
> > +                   if (region->userspace_addr == current_region-
> >guest_user_addr
> > +                           && region->guest_phys_addr ==
> current_region->guest_phys_addr
> > +                           && region->memory_size == current_region-
> >size) {
> > +                           free_mem_region(current_region);
> > +                           dev->mem->nregions--;
> > +                           return RTE_VHOST_MSG_RESULT_OK;
> > +                   }
>
> There is a lack of IOTLB entries invalidation here, as IOTLB entries in the cache
> could point to memory being unmapped in this function.
>
> Same comment for vring invalidation, as the vring adresses are not re-
> translated at each burst.
I will incorporate in the next version.
>
> > +           }
> > +   }
> > +
> > +   VHOST_CONFIG_LOG(dev->ifname, ERR, "failed to find region");
> > +   return RTE_VHOST_MSG_RESULT_ERR;
> > +}
> > +
> >   static bool
> >   vq_is_ready(struct virtio_net *dev, struct vhost_virtqueue *vq)
> >   {
> > diff --git a/lib/vhost/vhost_user.h b/lib/vhost/vhost_user.h index
> > ef486545ba..5a0e747b58 100644
> > --- a/lib/vhost/vhost_user.h
> > +++ b/lib/vhost/vhost_user.h
> > @@ -32,6 +32,7 @@
> >                                      (1ULL <<
> VHOST_USER_PROTOCOL_F_BACKEND_SEND_FD) | \
> >                                      (1ULL <<
> VHOST_USER_PROTOCOL_F_HOST_NOTIFIER) | \
> >                                      (1ULL <<
> VHOST_USER_PROTOCOL_F_PAGEFAULT) | \
> > +                                    (1ULL <<
> VHOST_USER_PROTOCOL_F_CONFIGURE_MEM_SLOTS) | \
> >                                      (1ULL <<
> VHOST_USER_PROTOCOL_F_STATUS))
> >
> >   typedef enum VhostUserRequest {
> > @@ -67,6 +68,9 @@ typedef enum VhostUserRequest {
> >     VHOST_USER_POSTCOPY_END = 30,
> >     VHOST_USER_GET_INFLIGHT_FD = 31,
> >     VHOST_USER_SET_INFLIGHT_FD = 32,
> > +   VHOST_USER_GET_MAX_MEM_SLOTS = 36,
> > +   VHOST_USER_ADD_MEM_REG = 37,
> > +   VHOST_USER_REM_MEM_REG = 38,
> >     VHOST_USER_SET_STATUS = 39,
> >     VHOST_USER_GET_STATUS = 40,
> >   } VhostUserRequest;
> > @@ -91,6 +95,11 @@ typedef struct VhostUserMemory {
> >     VhostUserMemoryRegion
> regions[VHOST_MEMORY_MAX_NREGIONS];
> >   } VhostUserMemory;
> >
> > +typedef struct VhostUserSingleMemReg {
> > +   uint64_t padding;
> > +   VhostUserMemoryRegion region;
> > +} VhostUserSingleMemReg;
> > +
> >   typedef struct VhostUserLog {
> >     uint64_t mmap_size;
> >     uint64_t mmap_offset;
> > @@ -186,6 +195,7 @@ typedef struct __rte_packed_begin VhostUserMsg {
> >             struct vhost_vring_state state;
> >             struct vhost_vring_addr addr;
> >             VhostUserMemory memory;
> > +           VhostUserSingleMemReg memory_single;
> >             VhostUserLog    log;
> >             struct vhost_iotlb_msg iotlb;
> >             VhostUserCryptoSessionParam crypto_session;