Re: [PATCH v5 3/4] vhost_user: support function defines for back-end

[Maxime Coquelin <maxime.coquelin@redhat.com>]

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@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.

>   	}
>   
>   	/* 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,