[cc +folks working on vfio-mdev migration] On Wed, 11 Apr 2018 19:20:14 +0200 Cédric Le Goater <[email protected]> wrote:
> Here is some context for this strange change request. > > On the POWER9 processor, the XIVE interrupt controller can control > interrupt sources using MMIO to trigger events, to EOI or to turn off > the sources. Priority management and interrupt acknowledgment is also > controlled by MMIO in the presenter subengine. > > These MMIO regions are exposed to guests in QEMU with a set of 'ram > device' memory mappings, similarly to VFIO, and the VMAs are populated > dynamically with the appropriate pages using a fault handler. > > But, these regions are an issue for migration. We need to discard the > associated RAMBlocks from the RAM state on the source VM and let the > destination VM rebuild the memory mappings on the new host in the > post_load() operation just before resuming the system. > > This is the goal of the following proposal. Does it make sense ? It > seems to be working enough to migrate a running guest but there might > be a better, more subtle, approach. Yulei, is this something you've run into with GVT-g migration? I don't see how we can read from or write to ram_device regions in a useful way during migration anyway, so the change initially looks correct to me. Thanks, Alex > Signed-off-by: Cédric Le Goater <[email protected]> > --- > migration/ram.c | 42 ++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 40 insertions(+), 2 deletions(-) > > diff --git a/migration/ram.c b/migration/ram.c > index 0e90efa09236..6404ccd046d8 100644 > --- a/migration/ram.c > +++ b/migration/ram.c > @@ -780,6 +780,10 @@ unsigned long migration_bitmap_find_dirty(RAMState *rs, > RAMBlock *rb, > unsigned long *bitmap = rb->bmap; > unsigned long next; > > + if (memory_region_is_ram_device(rb->mr)) { > + return size; > + } > + > if (rs->ram_bulk_stage && start > 0) { > next = start + 1; > } else { > @@ -826,6 +830,9 @@ uint64_t ram_pagesize_summary(void) > uint64_t summary = 0; > > RAMBLOCK_FOREACH(block) { > + if (memory_region_is_ram_device(block->mr)) { > + continue; > + } > summary |= block->page_size; > } > > @@ -850,6 +857,9 @@ static void migration_bitmap_sync(RAMState *rs) > qemu_mutex_lock(&rs->bitmap_mutex); > rcu_read_lock(); > RAMBLOCK_FOREACH(block) { > + if (memory_region_is_ram_device(block->mr)) { > + continue; > + } > migration_bitmap_sync_range(rs, block, 0, block->used_length); > } > rcu_read_unlock(); > @@ -1499,6 +1509,10 @@ static int ram_save_host_page(RAMState *rs, > PageSearchStatus *pss, > size_t pagesize_bits = > qemu_ram_pagesize(pss->block) >> TARGET_PAGE_BITS; > > + if (memory_region_is_ram_device(pss->block->mr)) { > + return 0; > + } > + > do { > tmppages = ram_save_target_page(rs, pss, last_stage); > if (tmppages < 0) { > @@ -1588,6 +1602,9 @@ uint64_t ram_bytes_total(void) > > rcu_read_lock(); > RAMBLOCK_FOREACH(block) { > + if (memory_region_is_ram_device(block->mr)) { > + continue; > + } > total += block->used_length; > } > rcu_read_unlock(); > @@ -1643,6 +1660,9 @@ static void ram_save_cleanup(void *opaque) > memory_global_dirty_log_stop(); > > QLIST_FOREACH_RCU(block, &ram_list.blocks, next) { > + if (memory_region_is_ram_device(block->mr)) { > + continue; > + } > g_free(block->bmap); > block->bmap = NULL; > g_free(block->unsentmap); > @@ -1710,6 +1730,9 @@ void > ram_postcopy_migrated_memory_release(MigrationState *ms) > unsigned long range = block->used_length >> TARGET_PAGE_BITS; > unsigned long run_start = find_next_zero_bit(bitmap, range, 0); > > + if (memory_region_is_ram_device(block->mr)) { > + continue; > + } > while (run_start < range) { > unsigned long run_end = find_next_bit(bitmap, range, run_start + > 1); > ram_discard_range(block->idstr, run_start << TARGET_PAGE_BITS, > @@ -1784,8 +1807,13 @@ static int > postcopy_each_ram_send_discard(MigrationState *ms) > int ret; > > RAMBLOCK_FOREACH(block) { > - PostcopyDiscardState *pds = > - postcopy_discard_send_init(ms, block->idstr); > + PostcopyDiscardState *pds; > + > + if (memory_region_is_ram_device(block->mr)) { > + continue; > + } > + > + pds = postcopy_discard_send_init(ms, block->idstr); > > /* > * Postcopy sends chunks of bitmap over the wire, but it > @@ -1996,6 +2024,10 @@ int ram_postcopy_send_discard_bitmap(MigrationState > *ms) > unsigned long *bitmap = block->bmap; > unsigned long *unsentmap = block->unsentmap; > > + if (memory_region_is_ram_device(block->mr)) { > + continue; > + } > + > if (!unsentmap) { > /* We don't have a safe way to resize the sentmap, so > * if the bitmap was resized it will be NULL at this > @@ -2151,6 +2183,9 @@ static void ram_list_init_bitmaps(void) > /* Skip setting bitmap if there is no RAM */ > if (ram_bytes_total()) { > QLIST_FOREACH_RCU(block, &ram_list.blocks, next) { > + if (memory_region_is_ram_device(block->mr)) { > + continue; > + } > pages = block->max_length >> TARGET_PAGE_BITS; > block->bmap = bitmap_new(pages); > bitmap_set(block->bmap, 0, pages); > @@ -2227,6 +2262,9 @@ static int ram_save_setup(QEMUFile *f, void *opaque) > qemu_put_be64(f, ram_bytes_total() | RAM_SAVE_FLAG_MEM_SIZE); > > RAMBLOCK_FOREACH(block) { > + if (memory_region_is_ram_device(block->mr)) { > + continue; > + } > qemu_put_byte(f, strlen(block->idstr)); > qemu_put_buffer(f, (uint8_t *)block->idstr, strlen(block->idstr)); > qemu_put_be64(f, block->used_length);
