* 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.
If this is always true of RAM devices (which I suspect it is). Interestingly, your patch comes less than 2 weeks after Lai Jiangshan's 'add capability to bypass the shared memory' https://lists.nongnu.org/archive/html/qemu-devel/2018-03/msg07511.html which is the only other case I think we've got of someone trying to avoid transmitting a block. We should try and merge the two sets to make them consistent; you've covered some more cases (the other patch wasn't expected to work with Postcopy anyway). (At this rate then we can expect another 20 for the year....) We should probably have: 1) A bool is_migratable_block(RAMBlock *) 2) A RAMBLOCK_FOREACH_MIGRATABLE(block) macro that is like RAMBLOCK_FOREACH but does the call to is_migratable_block then the changes should be mostly pretty tidy. A sanity check is probably needed on load as well, to give a neat error if for some reason the source transmits pages to you. One other thing I notice is your code changes ram_bytes_total(), where as the other patch avoids it; I think your code is actually more correct. Is there *any* case in existing QEMUs where we migrate ram devices succesfully, if so we've got to make it backwards compatible; but I think you're saying there isn't. Dave > Thanks, > > C. > > 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; > + } > + Now we shouldn't actually end up here should we - so I suggest an error_report and returning -EINVAL. > 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); > -- > 2.13.6 > -- Dr. David Alan Gilbert / [email protected] / Manchester, UK
