Re: [PATCH v3 4/5] vhost_user: support function defines for back-end

[fengchengwen <fengchengwen@huawei.com>]

On 11/4/2025 12:21 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
> essetially common functions to initialize memory, unmap a set of
> memory regions, perform register copy and align memory addresses.
> 
> Signed-off-by: Pravin M Bathija <pravin.bathija@dell.com>
> ---
>  lib/vhost/vhost_user.c | 80 +++++++++++++++++++++++++++++++++++-------
>  1 file changed, 68 insertions(+), 12 deletions(-)
> 
> diff --git a/lib/vhost/vhost_user.c b/lib/vhost/vhost_user.c
> index 168432e7d1..9a85f2fc92 100644
> --- a/lib/vhost/vhost_user.c
> +++ b/lib/vhost/vhost_user.c
> @@ -228,7 +228,17 @@ 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 +249,10 @@ 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);
>  	}
>  }
>  
> @@ -258,7 +266,7 @@ 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 +715,7 @@ 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 +819,10 @@ 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 +1260,13 @@ 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++) {

I think the using MAX_NREGIONS are most for convienent, but it will impact the performance,
because the rte_vhost_va_from_guest_pa() should iter the entire array.

I think we should keep the original impl: make sure the nregions entry of memory-region is
always valid.

Beside, where is the modification for rte_vhost_va_from_guest_pa()???

> +		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 +1293,10 @@ 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 +1401,46 @@ vhost_user_mmap_region(struct virtio_net *dev,
>  	return 0;
>  }
>  
> +static int
> +vhost_user_initialize_memory(struct virtio_net **pdev)

This function should be part of 3/5, else the 3/5 will compile fail

> +{
> +	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;

It should be 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,