[PATCH v5 3/4] vhost_user: support function defines for back-end
Bathija, Pravin
Pravin.Bathija at dell.com
Thu Jan 15 09:04:53 CET 2026
Dear Maxime,
Responses inline.
Internal Use - Confidential
> -----Original Message-----
> From: Maxime Coquelin <maxime.coquelin at redhat.com>
> Sent: Tuesday, January 6, 2026 8:29 AM
> To: Bathija, Pravin <Pravin.Bathija at dell.com>; dev at dpdk.org
> Cc: pravin.m.bathija.dev at gmail.com
> Subject: Re: [PATCH v5 3/4] vhost_user: support function defines for back-end
>
>
> [EXTERNAL EMAIL]
>
>
>
> On 11/13/25 1:44 PM, Pravin M Bathija wrote:
> > Here we define support functions which are called from the various
> > vhost-user back-end message functions like set memory table, get
> > memory slots, add memory region, remove memory region. These are
> > essentially common functions to initialize memory, unmap a set of
> > memory regions, perform register copy, align memory addresses and dma
> > map/unmap a single memory region.
> >
> > Signed-off-by: Pravin M Bathija <pravin.bathija at dell.com>
> > ---
> > lib/vhost/vhost_user.c | 150
> ++++++++++++++++++++++++++++++++++++++---
> > 1 file changed, 140 insertions(+), 10 deletions(-)
> >
> > diff --git a/lib/vhost/vhost_user.c b/lib/vhost/vhost_user.c index
> > 4bfb13fb98..7dc21fe42a 100644
> > --- a/lib/vhost/vhost_user.c
> > +++ b/lib/vhost/vhost_user.c
> > @@ -171,6 +171,80 @@ get_blk_size(int fd)
> > return ret == -1 ? (uint64_t)-1 : (uint64_t)stat.st_blksize;
> > }
> >
> > +static void
> > +async_dma_map_region(struct virtio_net *dev, struct
> > +rte_vhost_mem_region *reg, bool do_map) {
> > + uint32_t i;
> > + int ret = 0;
> > + int found = 0;
> > + struct guest_page *page;
> > +
> > + uint64_t reg_size = reg->size;
> > + uint64_t host_user_addr = reg->host_user_addr;
> > +
> > + for (i = 0; i < dev->nr_guest_pages; i++) {
> > + page = &dev->guest_pages[i];
> > + if (host_user_addr == page->host_user_addr) {
> > + found = 1;
> > + break;
> > + }
> > + }
> > +
> > + if (!found) {
> > + VHOST_CONFIG_LOG(dev->ifname, ERR, "DMA engine map:
> region not found");
> > + return;
> > + }
> > +
> > + if (do_map) {
> > + while (reg_size) {
> > + page = &dev->guest_pages[i];
> > + ret =
> rte_vfio_container_dma_map(RTE_VFIO_DEFAULT_CONTAINER_FD,
> > + page->host_user_addr,
> > + page->host_iova,
> > + page->size);
> > + if (ret) {
> > + if (rte_errno == ENODEV)
> > + return;
> > +
> > + /* DMA mapping errors won't stop
> VHOST_USER_SET_MEM_TABLE. */
> > + VHOST_CONFIG_LOG(dev->ifname, ERR,
> "DMA engine map failed");
> > + }
> > +
> > + reg_size -= page->size;
> > + ++i;
> > + if (i >= dev->nr_guest_pages) {
> > + /* shouldn't get here */
> > + VHOST_CONFIG_LOG(dev->ifname, ERR,
> "DMA engine map: No more pages");
> > + return;
> > + }
> > + }
> > + } else {
> > + while (reg_size) {
> > + page = &dev->guest_pages[i];
> > + ret =
> rte_vfio_container_dma_unmap(RTE_VFIO_DEFAULT_CONTAINER_FD,
> > + page->host_user_addr,
> > + page->host_iova,
> > + page->size);
> > + if (ret) {
> > + if (rte_errno == EINVAL)
> > + return;
> > +
> > + /* DMA mapping errors won't stop
> VHOST_USER_SET_MEM_TABLE. */
> > + VHOST_CONFIG_LOG(dev->ifname, ERR,
> "DMA engine unmap failed");
> > + }
> > +
> > + reg_size -= page->size;
> > + ++i;
> > + if (i >= dev->nr_guest_pages) {
> > + /* shouldn't get here */
> > + VHOST_CONFIG_LOG(dev->ifname, ERR,
> "DMA engine unmap: No more pages");
> > + return;
> > + }
> > + }
> > + }
> > +
> > +}
> > +
> > static void
> > async_dma_map(struct virtio_net *dev, bool do_map)
> > {
> > @@ -225,7 +299,17 @@ 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;
> > @@ -236,12 +320,10 @@ 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);
> > }
> > }
> >
> > @@ -255,7 +337,7 @@ 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;
> > }
> > @@ -704,7 +786,7 @@ 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, @@ -808,8 +890,10
> @@
> > 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);
> > @@ -1248,8 +1332,12 @@ vhost_user_postcopy_register(struct virtio_net
> *dev, int main_fd,
> > */
> > memory = &ctx->msg.payload.memory;
> > for (i = 0; i < memory->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++;
>
> How is it supposed to work?
> reg_msg_index is re-initialized to 0 at each iteration.
You are absolutely right, it is an oversight. reg_msg_index should be initialized before the for loop starts. I will make the necessary changes and retest.
>
> > }
> >
> > /* Send the addresses back to qemu */ @@ -1278,6 +1366,8 @@
> > 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++) {
> > reg = &dev->mem->regions[i];
> > + if (reg->host_user_addr == 0)
> > + continue;
> > if (vhost_user_postcopy_region_register(dev, reg) < 0)
> > return -1;
> > }
> > @@ -1382,6 +1472,46 @@ 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 = VHOST_MEMORY_MAX_NREGIONS;
> > + 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,
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