Re: [PATCH v8 29/30] packet: Refactor vhost-user memory region handling

On Tue, Aug 05, 2025 at 05:46:27PM +0200, Laurent Vivier wrote:

This patch refactors the handling of vhost-user memory regions by introducing a new `struct vdev_memory` to encapsulate the regions array and their count (`nregions`) within the main `vu_dev` structure.

This new `vdev_memory` structure is then passed to the packet pool by re-using the existing `p->buf` field. A `p->buf_size` of 0 indicates that `p->buf` holds a pointer to `struct vdev_memory` instead of a regular packet buffer. A new helper, `get_vdev_memory()`, is added to abstract this access pattern.

Signed-off-by: Laurent Vivier --- packet.c | 18 ++++++++++++++++-- packet.h | 6 ++++-- tap.c | 4 ++-- tap.h | 1 - vhost_user.c | 28 +++++++++++----------------- virtio.c | 4 ++-- virtio.h | 18 ++++++++++++++---- vu_common.c | 22 ++++++++++++---------- 8 files changed, 61 insertions(+), 40 deletions(-)

diff --git a/packet.c b/packet.c index cbc43c2fc22d..4b93688509a4 100644 --- a/packet.c +++ b/packet.c @@ -22,6 +22,20 @@ #include "util.h" #include "log.h"

+/** + * get_vdev_memory() - Return a pointer to the memory regions of the pool + * @p: Packet pool + * + * Return: Null if none, otherwise a pointer to vdev_memory structure + */ +static struct vdev_memory *get_vdev_memory(const struct pool *p) +{ + if (p->buf_size) + return NULL; + + return (struct vdev_memory *)p->buf; +} + /** * packet_check_range() - Check if a memory range is valid for a pool * @p: Packet pool @@ -41,10 +55,10 @@ static int packet_check_range(const struct pool *p, const char *ptr, size_t len, return -1; }

- if (p->buf_size == 0) { + if (get_vdev_memory(p)) { int ret;

- ret = vu_packet_check_range((void *)p->buf, ptr, len); + ret = vu_packet_check_range(get_vdev_memory(p), ptr, len);

Seems like it would be marginally more natural to assign get_vdev_memory() to a temporary in the if, then re-use it here.

if (ret == -1) debug("cannot find region, %s:%i", func, line); diff --git a/packet.h b/packet.h index 43b9022075d1..e51cbd19fdc4 100644 --- a/packet.h +++ b/packet.h @@ -8,6 +8,7 @@

#include #include "iov.h" +#include "virtio.h"

/* Maximum size of a single packet stored in pool, including headers */ #define PACKET_MAX_LEN ((size_t)UINT16_MAX) @@ -15,7 +16,7 @@ /** * struct pool - Generic pool of packets stored in a buffer * @buf: Buffer storing packet descriptors, - * a struct vu_dev_region array for passt vhost-user mode + * a struct vdev_region for passt vhost-user mode * @buf_size: Total size of buffer, * 0 for passt vhost-user mode * @size: Number of usable descriptors for the pool @@ -30,7 +31,8 @@ struct pool { struct iovec pkt[]; };

-int vu_packet_check_range(void *buf, const char *ptr, size_t len); +int vu_packet_check_range(struct vdev_memory *memory, + const char *ptr, size_t len); void packet_add_do(struct pool *p, struct iov_tail *data, const char *func, int line); bool packet_get_do(const struct pool *p, const size_t idx, diff --git a/tap.c b/tap.c index bbc786468455..9fd00915bb01 100644 --- a/tap.c +++ b/tap.c @@ -1458,7 +1458,7 @@ static void tap_sock_tun_init(struct ctx *c) * @base: Buffer base * @size Buffer size */ -void tap_sock_update_pool(void *base, size_t size) +static void tap_sock_update_pool(void *base, size_t size) { int i;

@@ -1479,8 +1479,8 @@ void tap_sock_update_pool(void *base, size_t size) void tap_backend_init(struct ctx *c) { if (c->mode == MODE_VU) { - tap_sock_update_pool(NULL, 0); vu_init(c); + tap_sock_update_pool(&c->vdev->memory, 0); } else { tap_sock_update_pool(pkt_buf, sizeof(pkt_buf)); } diff --git a/tap.h b/tap.h index ce5510882d5d..21db4d219ecb 100644 --- a/tap.h +++ b/tap.h @@ -115,7 +115,6 @@ void tap_handler_passt(struct ctx *c, uint32_t events, const struct timespec *now); int tap_sock_unix_open(char *sock_path); void tap_sock_reset(struct ctx *c); -void tap_sock_update_pool(void *base, size_t size); void tap_backend_init(struct ctx *c); void tap_flush_pools(void); void tap_handler(struct ctx *c, const struct timespec *now); diff --git a/vhost_user.c b/vhost_user.c index c1522d549f00..f97ec6064cac 100644 --- a/vhost_user.c +++ b/vhost_user.c @@ -137,8 +137,8 @@ static void *qva_to_va(struct vu_dev *dev, uint64_t qemu_addr) unsigned int i;

/* Find matching memory region. */ - for (i = 0; i < dev->nregions; i++) { - const struct vu_dev_region *r = &dev->regions[i]; + for (i = 0; i < dev->memory.nregions; i++) { + const struct vu_dev_region *r = &dev->memory.regions[i];

if ((qemu_addr >= r->qva) && (qemu_addr < (r->qva + r->size))) { /* NOLINTNEXTLINE(performance-no-int-to-ptr) */ @@ -428,8 +428,8 @@ static bool vu_set_mem_table_exec(struct vu_dev *vdev, struct vhost_user_memory m = vmsg->payload.memory, *memory = &m; unsigned int i;

- for (i = 0; i < vdev->nregions; i++) { - const struct vu_dev_region *r = &vdev->regions[i]; + for (i = 0; i < vdev->memory.nregions; i++) { + const struct vu_dev_region *r = &vdev->memory.regions[i];

if (r->mmap_addr) { /* NOLINTNEXTLINE(performance-no-int-to-ptr) */ @@ -437,12 +437,12 @@ static bool vu_set_mem_table_exec(struct vu_dev *vdev, r->size + r->mmap_offset); } } - vdev->nregions = memory->nregions; + vdev->memory.nregions = memory->nregions;

debug("vhost-user nregions: %u", memory->nregions); - for (i = 0; i < vdev->nregions; i++) { + for (i = 0; i < vdev->memory.nregions; i++) { struct vhost_user_memory_region *msg_region = &memory->regions[i]; - struct vu_dev_region *dev_region = &vdev->regions[i]; + struct vu_dev_region *dev_region = &vdev->memory.regions[i]; void *mmap_addr;

debug("vhost-user region %d", i); @@ -484,13 +484,7 @@ static bool vu_set_mem_table_exec(struct vu_dev *vdev, } }

- /* As vu_packet_check_range() has no access to the number of - * memory regions, mark the end of the array with mmap_addr = 0 - */ - ASSERT(vdev->nregions < VHOST_USER_MAX_RAM_SLOTS - 1); - vdev->regions[vdev->nregions].mmap_addr = 0; - - tap_sock_update_pool(vdev->regions, 0); + ASSERT(vdev->memory.nregions < VHOST_USER_MAX_RAM_SLOTS);

It looks like the assertion is changing threshold by one, and I'm not sure why.

return false; } @@ -1106,8 +1100,8 @@ void vu_cleanup(struct vu_dev *vdev) vq->vring.avail = 0; }

- for (i = 0; i < vdev->nregions; i++) { - const struct vu_dev_region *r = &vdev->regions[i]; + for (i = 0; i < vdev->memory.nregions; i++) { + const struct vu_dev_region *r = &vdev->memory.regions[i];

if (r->mmap_addr) { /* NOLINTNEXTLINE(performance-no-int-to-ptr) */ @@ -1115,7 +1109,7 @@ void vu_cleanup(struct vu_dev *vdev) r->size + r->mmap_offset); } } - vdev->nregions = 0; + vdev->memory.nregions = 0;

vu_close_log(vdev);

diff --git a/virtio.c b/virtio.c index ed7842b4c78a..bd388c2dfc7f 100644 --- a/virtio.c +++ b/virtio.c @@ -102,8 +102,8 @@ static void *vu_gpa_to_va(const struct vu_dev *dev, uint64_t *plen, return NULL;

/* Find matching memory region. */ - for (i = 0; i < dev->nregions; i++) { - const struct vu_dev_region *r = &dev->regions[i]; + for (i = 0; i < dev->memory.nregions; i++) { + const struct vu_dev_region *r = &dev->memory.regions[i];

if ((guest_addr >= r->gpa) && (guest_addr < (r->gpa + r->size))) { diff --git a/virtio.h b/virtio.h index 32757458ea95..b55cc4042521 100644 --- a/virtio.h +++ b/virtio.h @@ -96,11 +96,22 @@ struct vu_dev_region { */ #define VHOST_USER_MAX_RAM_SLOTS 32

+/** + * struct vdev_memory - Describes the shared memory regions for a vhost-user + * device + * @nregions: Number of shared memory regions + * @regions: Guest shared memory regions + */ +struct vdev_memory { + uint32_t nregions; + struct vu_dev_region regions[VHOST_USER_MAX_RAM_SLOTS]; +}; + /** * struct vu_dev - vhost-user device information * @context: Execution context - * @nregions: Number of shared memory regions - * @regions: Guest shared memory regions + * @memory: Shared memory regions + * @vq: Virtqueues of the device * @features: Vhost-user features * @protocol_features: Vhost-user protocol features * @log_call_fd: Eventfd to report logging update @@ -109,8 +120,7 @@ struct vu_dev_region { */ struct vu_dev { struct ctx *context; - uint32_t nregions; - struct vu_dev_region regions[VHOST_USER_MAX_RAM_SLOTS]; + struct vdev_memory memory; struct vu_virtq vq[VHOST_USER_MAX_QUEUES]; uint64_t features; uint64_t protocol_features; diff --git a/vu_common.c b/vu_common.c index b77b21420c57..b716070ea3c3 100644 --- a/vu_common.c +++ b/vu_common.c @@ -25,26 +25,28 @@ /** * vu_packet_check_range() - Check if a given memory zone is contained in * a mapped guest memory region - * @buf: Array of the available memory regions + * @memory: Array of the available memory regions * @ptr: Start of desired data range - * @size: Length of desired data range + * @len: Length of desired data range * * Return: 0 if the zone is in a mapped memory region, -1 otherwise */ -int vu_packet_check_range(void *buf, const char *ptr, size_t len) +int vu_packet_check_range(struct vdev_memory *memory, + const char *ptr, size_t len) { - struct vu_dev_region *dev_region; + struct vu_dev_region *dev_region = memory->regions; + unsigned int i;

- for (dev_region = buf; dev_region->mmap_addr; dev_region++) { - uintptr_t base_addr = dev_region->mmap_addr + - dev_region->mmap_offset; + for (i = 0; i < memory->nregions; i++) { + uintptr_t base_addr = dev_region[i].mmap_addr + + dev_region[i].mmap_offset; /* NOLINTNEXTLINE(performance-no-int-to-ptr) */ const char *base = (const char *)base_addr;

- ASSERT(base_addr >= dev_region->mmap_addr); + ASSERT(base_addr >= dev_region[i].mmap_addr);

- if (len <= dev_region->size && base <= ptr && - (size_t)(ptr - base) <= dev_region->size - len) + if (len <= dev_region[i].size && base <= ptr && + (size_t)(ptr - base) <= dev_region[i].size - len) return 0; }

-- David Gibson (he or they) | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you, not the other way | around. http://www.ozlabs.org/~dgibson