On 3/4/25 23:04, Maciej S. Szmigiero wrote:
> From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
>
> Allow capping the maximum count of in-flight VFIO device state buffers
> queued at the destination, otherwise a malicious QEMU source could
> theoretically cause the target QEMU to allocate unlimited amounts of memory
> for buffers-in-flight.
>
> Since this is not expected to be a realistic threat in most of VFIO live
> migration use cases and the right value depends on the particular setup
> disable the limit by default by setting it to UINT64_MAX.
I agree with Avihai that a limit on bytes would make more sense.
-rc0 is in ~2w. We have time to prepare a patch for this.
Should there be a correlation with :
/*
* This is an arbitrary size based on migration of mlx5 devices, where typically
* total device migration size is on the order of 100s of MB. Testing with
* larger values, e.g. 128MB and 1GB, did not show a performance improvement.
*/
#define VFIO_MIG_DEFAULT_DATA_BUFFER_SIZE (1 * MiB)
Thanks,
C.
> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
> ---
> hw/vfio/migration-multifd.c | 16 ++++++++++++++++
> hw/vfio/pci.c | 9 +++++++++
> include/hw/vfio/vfio-common.h | 1 +
> 3 files changed, 26 insertions(+)
>
> diff --git a/hw/vfio/migration-multifd.c b/hw/vfio/migration-multifd.c
> index 233724710b37..d6dabaf869ca 100644
> --- a/hw/vfio/migration-multifd.c
> +++ b/hw/vfio/migration-multifd.c
> @@ -54,6 +54,7 @@ typedef struct VFIOMultifd {
> QemuMutex load_bufs_mutex; /* Lock order: this lock -> BQL */
> uint32_t load_buf_idx;
> uint32_t load_buf_idx_last;
> + uint32_t load_buf_queued_pending_buffers;
> } VFIOMultifd;
>
> static void vfio_state_buffer_clear(gpointer data)
> @@ -125,6 +126,17 @@ static bool vfio_load_state_buffer_insert(VFIODevice *vbasedev,
>
> assert(packet->idx >= multifd->load_buf_idx);
>
> + multifd->load_buf_queued_pending_buffers++;
> + if (multifd->load_buf_queued_pending_buffers >
> + vbasedev->migration_max_queued_buffers) {
> + error_setg(errp,
> + "%s: queuing state buffer %" PRIu32
> + " would exceed the max of %" PRIu64,
> + vbasedev->name, packet->idx,
> + vbasedev->migration_max_queued_buffers);
> + return false;
> + }
> +
> lb->data = g_memdup2(&packet->data, packet_total_size - sizeof(*packet));
> lb->len = packet_total_size - sizeof(*packet);
> lb->is_present = true;
> @@ -381,6 +393,9 @@ static bool vfio_load_bufs_thread(void *opaque, bool *should_quit, Error **errp)
> goto thread_exit;
> }
>
> + assert(multifd->load_buf_queued_pending_buffers > 0);
> + multifd->load_buf_queued_pending_buffers--;
> +
> if (multifd->load_buf_idx == multifd->load_buf_idx_last - 1) {
> trace_vfio_load_state_device_buffer_end(vbasedev->name);
> }
> @@ -417,6 +432,7 @@ static VFIOMultifd *vfio_multifd_new(void)
>
> multifd->load_buf_idx = 0;
> multifd->load_buf_idx_last = UINT32_MAX;
> + multifd->load_buf_queued_pending_buffers = 0;
> qemu_cond_init(&multifd->load_bufs_buffer_ready_cond);
>
> multifd->load_bufs_thread_running = false;
> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> index 21605bac2fb0..ce407f971000 100644
> --- a/hw/vfio/pci.c
> +++ b/hw/vfio/pci.c
> @@ -3383,6 +3383,8 @@ static const Property vfio_pci_dev_properties[] = {
> vbasedev.migration_multifd_transfer,
> vfio_pci_migration_multifd_transfer_prop, OnOffAuto,
> .set_default = true, .defval.i = ON_OFF_AUTO_AUTO),
> + DEFINE_PROP_UINT64("x-migration-max-queued-buffers", VFIOPCIDevice,
> + vbasedev.migration_max_queued_buffers, UINT64_MAX),
> DEFINE_PROP_BOOL("migration-events", VFIOPCIDevice,
> vbasedev.migration_events, false),
> DEFINE_PROP_BOOL("x-no-mmap", VFIOPCIDevice, vbasedev.no_mmap, false),
> @@ -3444,6 +3446,13 @@ static void vfio_pci_dev_class_init(ObjectClass *klass, void *data)
> "x-migration-multifd-transfer",
> "Transfer this device state via "
> "multifd channels when live migrating it");
> + object_class_property_set_description(klass, /* 10.0 */
> + "x-migration-max-queued-buffers",
> + "Maximum count of in-flight VFIO "
> + "device state buffers queued at the "
> + "destination when doing live "
> + "migration of device state via "
> + "multifd channels");
> }
>
> static const TypeInfo vfio_pci_dev_info = {
> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> index 04b123a6c929..c033c3c5134f 100644
> --- a/include/hw/vfio/vfio-common.h
> +++ b/include/hw/vfio/vfio-common.h
> @@ -155,6 +155,7 @@ typedef struct VFIODevice {
> bool ram_block_discard_allowed;
> OnOffAuto enable_migration;
> OnOffAuto migration_multifd_transfer;
> + uint64_t migration_max_queued_buffers;
> bool migration_events;
> VFIODeviceOps *ops;
> unsigned int num_irqs;
>