Avihai Horon <avih...@nvidia.com> wrote:
> Currently, if IOMMU of a VFIO container doesn't support dirty page
> tracking, migration is blocked completely. This is because a DMA-able
> VFIO device can dirty RAM pages without updating QEMU about it, thus
> breaking the migration.
>
> However, this doesn't mean that migration can't be done at all. If
> migration pre-copy phase is skipped, the VFIO device doesn't have a
> chance to dirty RAM pages that have been migrated already, thus
> eliminating the problem previously mentioned.
>
> Hence, in such case allow migration but skip pre-copy phase.
>
> Signed-off-by: Avihai Horon <avih...@nvidia.com>
I don't know (TM).
Several issues:
- Patch is ugly as hell (ok, that depends on taste)
- It changes migration_iteration_run() instead of directly
migration_thread.
- There is already another case where we skip the sending of RAM
(localhost migration with shared memory)
In migration/ram.c:
static int ram_find_and_save_block(RAMState *rs, bool last_stage)
{
PageSearchStatus pss;
int pages = 0;
bool again, found;
/* No dirty page as there is zero RAM */
if (!ram_bytes_total()) {
return pages;
}
This is the other place where we _don't_ send any RAM at all.
I don't have a great idea about how to make things clear at a higher
level, I have to think about this.
Later, Juan.
> ---
> hw/vfio/migration.c | 9 ++++++++-
> migration/migration.c | 5 +++++
> migration/migration.h | 3 +++
> 3 files changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> index 21e8f9d4d4..d4b6653026 100644
> --- a/hw/vfio/migration.c
> +++ b/hw/vfio/migration.c
> @@ -863,10 +863,17 @@ int vfio_migration_probe(VFIODevice *vbasedev, Error
> **errp)
> struct vfio_region_info *info = NULL;
> int ret = -ENOTSUP;
>
> - if (!vbasedev->enable_migration || !container->dirty_pages_supported) {
> + if (!vbasedev->enable_migration) {
> goto add_blocker;
> }
>
> + if (!container->dirty_pages_supported) {
> + warn_report(
> + "%s: IOMMU of the device's VFIO container doesn't support dirty
> page tracking, migration pre-copy phase will be skipped",
> + vbasedev->name);
> + migrate_get_current()->skip_precopy = true;
> + }
> +
> ret = vfio_get_dev_region_info(vbasedev,
> VFIO_REGION_TYPE_MIGRATION_DEPRECATED,
> VFIO_REGION_SUBTYPE_MIGRATION_DEPRECATED,
> diff --git a/migration/migration.c b/migration/migration.c
> index 5a31b23bd6..668343508d 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -3593,6 +3593,11 @@ static MigIterateState
> migration_iteration_run(MigrationState *s)
> uint64_t pending_size, pend_pre, pend_compat, pend_post;
> bool in_postcopy = s->state == MIGRATION_STATUS_POSTCOPY_ACTIVE;
>
> + if (s->skip_precopy) {
> + migration_completion(s);
> + return MIG_ITERATE_BREAK;
> + }
> +
> qemu_savevm_state_pending(s->to_dst_file, s->threshold_size, &pend_pre,
> &pend_compat, &pend_post);
> pending_size = pend_pre + pend_compat + pend_post;
> diff --git a/migration/migration.h b/migration/migration.h
> index a863032b71..876713e7e1 100644
> --- a/migration/migration.h
> +++ b/migration/migration.h
> @@ -332,6 +332,9 @@ struct MigrationState {
> * This save hostname when out-going migration starts
> */
> char *hostname;
> +
> + /* Whether to skip pre-copy phase of migration or not */
> + bool skip_precopy;
> };
>
> void migrate_set_state(int *state, int old_state, int new_state);
