Having multiple vhost devices, some filtering out fd-less memslots and some not, can mess up the "used_memslot" accounting. Consequently our "free memslot" checks become unreliable and we might run out of free memslots at runtime later. An example sequence which can trigger a potential issue that involves different vhost backends (vhost-kernel and vhost-user) and hotplugged memory devices can be found at [1]. Let's make the filtering mechanism less generic and distinguish between backends that support private memslots (without a fd) and ones that only support shared memslots (with a fd). Track the used_memslots for both cases separately and use the corresponding value when required. Note: Most probably we should filter out MAP_PRIVATE fd-based RAM regions (for example, via memory-backend-memfd,...,shared=off or as default with memory-backend-file) as well. When not using MAP_SHARED, it might not work as expected. Add a TODO for now. [1] https://lkml.kernel.org/r/fad9136f-08d3-3fd9-71a1-502069c000cf@xxxxxxxxxx Fixes: 988a27754bbb ("vhost: allow backends to filter memory sections") Cc: Tiwei Bie <tiwei.bie@xxxxxxxxx> Acked-by: Igor Mammedov <imammedo@xxxxxxxxxx> Reviewed-by: Peter Xu <peterx@xxxxxxxxxx> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> --- hw/virtio/vhost-user.c | 7 ++-- hw/virtio/vhost.c | 56 ++++++++++++++++++++++++++----- include/hw/virtio/vhost-backend.h | 5 ++- 3 files changed, 52 insertions(+), 16 deletions(-) diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c index 8dcf049d42..1e7553352a 100644 --- a/hw/virtio/vhost-user.c +++ b/hw/virtio/vhost-user.c @@ -2500,10 +2500,9 @@ vhost_user_crypto_close_session(struct vhost_dev *dev, uint64_t session_id) return 0; } -static bool vhost_user_mem_section_filter(struct vhost_dev *dev, - MemoryRegionSection *section) +static bool vhost_user_no_private_memslots(struct vhost_dev *dev) { - return memory_region_get_fd(section->mr) >= 0; + return true; } static int vhost_user_get_inflight_fd(struct vhost_dev *dev, @@ -2746,6 +2745,7 @@ const VhostOps user_ops = { .vhost_backend_init = vhost_user_backend_init, .vhost_backend_cleanup = vhost_user_backend_cleanup, .vhost_backend_memslots_limit = vhost_user_memslots_limit, + .vhost_backend_no_private_memslots = vhost_user_no_private_memslots, .vhost_set_log_base = vhost_user_set_log_base, .vhost_set_mem_table = vhost_user_set_mem_table, .vhost_set_vring_addr = vhost_user_set_vring_addr, @@ -2772,7 +2772,6 @@ const VhostOps user_ops = { .vhost_set_config = vhost_user_set_config, .vhost_crypto_create_session = vhost_user_crypto_create_session, .vhost_crypto_close_session = vhost_user_crypto_close_session, - .vhost_backend_mem_section_filter = vhost_user_mem_section_filter, .vhost_get_inflight_fd = vhost_user_get_inflight_fd, .vhost_set_inflight_fd = vhost_user_set_inflight_fd, .vhost_dev_start = vhost_user_dev_start, diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c index e2f6ffb446..c1e6148833 100644 --- a/hw/virtio/vhost.c +++ b/hw/virtio/vhost.c @@ -45,20 +45,33 @@ static struct vhost_log *vhost_log; static struct vhost_log *vhost_log_shm; +/* Memslots used by backends that support private memslots (without an fd). */ static unsigned int used_memslots; + +/* Memslots used by backends that only support shared memslots (with an fd). */ +static unsigned int used_shared_memslots; + static QLIST_HEAD(, vhost_dev) vhost_devices = QLIST_HEAD_INITIALIZER(vhost_devices); bool vhost_has_free_slot(void) { - unsigned int slots_limit = ~0U; + unsigned int free = UINT_MAX; struct vhost_dev *hdev; QLIST_FOREACH(hdev, &vhost_devices, entry) { unsigned int r = hdev->vhost_ops->vhost_backend_memslots_limit(hdev); - slots_limit = MIN(slots_limit, r); + unsigned int cur_free; + + if (hdev->vhost_ops->vhost_backend_no_private_memslots && + hdev->vhost_ops->vhost_backend_no_private_memslots(hdev)) { + cur_free = r - used_shared_memslots; + } else { + cur_free = r - used_memslots; + } + free = MIN(free, cur_free); } - return slots_limit > used_memslots; + return free > 0; } static void vhost_dev_sync_region(struct vhost_dev *dev, @@ -474,8 +487,7 @@ static int vhost_verify_ring_mappings(struct vhost_dev *dev, * vhost_section: identify sections needed for vhost access * * We only care about RAM sections here (where virtqueue and guest - * internals accessed by virtio might live). If we find one we still - * allow the backend to potentially filter it out of our list. + * internals accessed by virtio might live). */ static bool vhost_section(struct vhost_dev *dev, MemoryRegionSection *section) { @@ -502,8 +514,16 @@ static bool vhost_section(struct vhost_dev *dev, MemoryRegionSection *section) return false; } - if (dev->vhost_ops->vhost_backend_mem_section_filter && - !dev->vhost_ops->vhost_backend_mem_section_filter(dev, section)) { + /* + * Some backends (like vhost-user) can only handle memory regions + * that have an fd (can be mapped into a different process). Filter + * the ones without an fd out, if requested. + * + * TODO: we might have to limit to MAP_SHARED as well. + */ + if (memory_region_get_fd(section->mr) < 0 && + dev->vhost_ops->vhost_backend_no_private_memslots && + dev->vhost_ops->vhost_backend_no_private_memslots(dev)) { trace_vhost_reject_section(mr->name, 2); return false; } @@ -568,7 +588,14 @@ static void vhost_commit(MemoryListener *listener) dev->n_mem_sections * sizeof dev->mem->regions[0]; dev->mem = g_realloc(dev->mem, regions_size); dev->mem->nregions = dev->n_mem_sections; - used_memslots = dev->mem->nregions; + + if (dev->vhost_ops->vhost_backend_no_private_memslots && + dev->vhost_ops->vhost_backend_no_private_memslots(dev)) { + used_shared_memslots = dev->mem->nregions; + } else { + used_memslots = dev->mem->nregions; + } + for (i = 0; i < dev->n_mem_sections; i++) { struct vhost_memory_region *cur_vmr = dev->mem->regions + i; struct MemoryRegionSection *mrs = dev->mem_sections + i; @@ -1400,6 +1427,7 @@ int vhost_dev_init(struct vhost_dev *hdev, void *opaque, VhostBackendType backend_type, uint32_t busyloop_timeout, Error **errp) { + unsigned int used; uint64_t features; int i, r, n_initialized_vqs = 0; @@ -1495,7 +1523,17 @@ int vhost_dev_init(struct vhost_dev *hdev, void *opaque, memory_listener_register(&hdev->memory_listener, &address_space_memory); QLIST_INSERT_HEAD(&vhost_devices, hdev, entry); - if (used_memslots > hdev->vhost_ops->vhost_backend_memslots_limit(hdev)) { + /* + * The listener we registered properly updated the corresponding counter. + * So we can trust that these values are accurate. + */ + if (hdev->vhost_ops->vhost_backend_no_private_memslots && + hdev->vhost_ops->vhost_backend_no_private_memslots(hdev)) { + used = used_shared_memslots; + } else { + used = used_memslots; + } + if (used > hdev->vhost_ops->vhost_backend_memslots_limit(hdev)) { error_setg(errp, "vhost backend memory slots limit is less" " than current number of present memory slots"); r = -EINVAL; diff --git a/include/hw/virtio/vhost-backend.h b/include/hw/virtio/vhost-backend.h index 31a251a9f5..df2821ddae 100644 --- a/include/hw/virtio/vhost-backend.h +++ b/include/hw/virtio/vhost-backend.h @@ -108,8 +108,7 @@ typedef int (*vhost_crypto_create_session_op)(struct vhost_dev *dev, typedef int (*vhost_crypto_close_session_op)(struct vhost_dev *dev, uint64_t session_id); -typedef bool (*vhost_backend_mem_section_filter_op)(struct vhost_dev *dev, - MemoryRegionSection *section); +typedef bool (*vhost_backend_no_private_memslots_op)(struct vhost_dev *dev); typedef int (*vhost_get_inflight_fd_op)(struct vhost_dev *dev, uint16_t queue_size, @@ -138,6 +137,7 @@ typedef struct VhostOps { vhost_backend_init vhost_backend_init; vhost_backend_cleanup vhost_backend_cleanup; vhost_backend_memslots_limit vhost_backend_memslots_limit; + vhost_backend_no_private_memslots_op vhost_backend_no_private_memslots; vhost_net_set_backend_op vhost_net_set_backend; vhost_net_set_mtu_op vhost_net_set_mtu; vhost_scsi_set_endpoint_op vhost_scsi_set_endpoint; @@ -172,7 +172,6 @@ typedef struct VhostOps { vhost_set_config_op vhost_set_config; vhost_crypto_create_session_op vhost_crypto_create_session; vhost_crypto_close_session_op vhost_crypto_close_session; - vhost_backend_mem_section_filter_op vhost_backend_mem_section_filter; vhost_get_inflight_fd_op vhost_get_inflight_fd; vhost_set_inflight_fd_op vhost_set_inflight_fd; vhost_dev_start_op vhost_dev_start; -- 2.41.0
