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vhost: Rework memslot filtering and fix "used_memslot" tracking

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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@redhat.com

Message-ID: <20230926185738.277351-2-david@redhat.com>
Fixes: 988a27754b ("vhost: allow backends to filter memory sections")
Cc: Tiwei Bie <tiwei.bie@intel.com>
Acked-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
This commit is contained in:
David Hildenbrand 2023-09-26 20:57:21 +02:00
parent a51e5124a6
commit 552b25229c
3 changed files with 52 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
hw/virtio/vhost-user.c
View File

@ -2622,10 +2622,9 @@ 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,
@ -2868,6 +2867,7 @@ 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,
@ -2894,7 +2894,6 @@ 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,

54
hw/virtio/vhost.c
View File

@ -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;
}
return slots_limit > used_memslots;
free = MIN(free, cur_free);
}
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;
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;

5
include/hw/virtio/vhost-backend.h
View File

@ -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;