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authorDavid Hildenbrand <david@redhat.com>2023-09-26 20:57:21 +0200
committerDavid Hildenbrand <david@redhat.com>2023-10-12 14:15:21 +0200
commit552b25229cf7c65d31ac9a60b1d9202672dd9c61 (patch)
treeb2162fe389d7b1ff920c034aae544779ec0ea624 /hw/virtio/vhost.c
parenta51e5124a655b3dad80b36b18547cb1eca2c5eb2 (diff)
vhost: Rework memslot filtering and fix "used_memslot" tracking
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: 988a27754bbb ("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>
Diffstat (limited to 'hw/virtio/vhost.c')
-rw-r--r--hw/virtio/vhost.c56
1 files changed, 47 insertions, 9 deletions
diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 9cfac40fde..0edd31a7e8 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;