On 21.02.20 16:14, Dr. David Alan Gilbert wrote: > * David Hildenbrand (da...@redhat.com) wrote: >> Resizing while migrating is dangerous and does not work as expected. >> The whole migration code works on the usable_length of ram blocks and does >> not expect this to change at random points in time. >> >> In the case of precopy, the ram block size must not change on the source, >> after syncing the RAM block list in ram_save_setup(), so as long as the >> guest is still running on the source. >> >> Resizing can be trigger *after* (but not during) a reset in >> ACPI code by the guest >> - hw/arm/virt-acpi-build.c:acpi_ram_update() >> - hw/i386/acpi-build.c:acpi_ram_update() >> >> Use the ram block notifier to get notified about resizes. Let's simply >> cancel migration and indicate the reason. We'll continue running on the >> source. No harm done. >> >> Update the documentation. Postcopy will be handled separately. >> >> Cc: "Dr. David Alan Gilbert" <dgilb...@redhat.com> >> Cc: Juan Quintela <quint...@redhat.com> >> Cc: Eduardo Habkost <ehabk...@redhat.com> >> Cc: Paolo Bonzini <pbonz...@redhat.com> >> Cc: Igor Mammedov <imamm...@redhat.com> >> Cc: "Michael S. Tsirkin" <m...@redhat.com> >> Cc: Richard Henderson <richard.hender...@linaro.org> >> Cc: Shannon Zhao <shannon.z...@linaro.org> >> Cc: Alex Bennée <alex.ben...@linaro.org> >> Cc: Peter Xu <pet...@redhat.com> >> Signed-off-by: David Hildenbrand <da...@redhat.com> >> --- >> exec.c | 5 +++-- >> include/exec/memory.h | 10 ++++++---- >> migration/migration.c | 9 +++++++-- >> migration/migration.h | 1 + >> migration/ram.c | 41 +++++++++++++++++++++++++++++++++++++++++ >> 5 files changed, 58 insertions(+), 8 deletions(-) >> >> diff --git a/exec.c b/exec.c >> index b75250e773..8b015821d6 100644 >> --- a/exec.c >> +++ b/exec.c >> @@ -2120,8 +2120,9 @@ static int memory_try_enable_merging(void *addr, >> size_t len) >> return qemu_madvise(addr, len, QEMU_MADV_MERGEABLE); >> } >> >> -/* Only legal before guest might have detected the memory size: e.g. on >> - * incoming migration, or right after reset. >> +/* >> + * Resizing RAM while migrating can result in the migration being canceled. >> + * Care has to be taken if the guest might have already detected the memory. >> * >> * As memory core doesn't know how is memory accessed, it is up to >> * resize callback to update device state and/or add assertions to detect >> diff --git a/include/exec/memory.h b/include/exec/memory.h >> index e85b7de99a..de111347e8 100644 >> --- a/include/exec/memory.h >> +++ b/include/exec/memory.h >> @@ -113,7 +113,7 @@ typedef struct IOMMUNotifier IOMMUNotifier; >> #define RAM_SHARED (1 << 1) >> >> /* Only a portion of RAM (used_length) is actually used, and migrated. >> - * This used_length size can change across reboots. >> + * Resizing RAM while migrating can result in the migration being canceled. >> */ >> #define RAM_RESIZEABLE (1 << 2) >> >> @@ -843,7 +843,9 @@ void >> memory_region_init_ram_shared_nomigrate(MemoryRegion *mr, >> * RAM. Accesses into the region will >> * modify memory directly. Only an >> initial >> * portion of this RAM is actually used. >> - * The used size can change across >> reboots. >> + * Changing the size while migrating >> + * can result in the migration being >> + * canceled. >> * >> * @mr: the #MemoryRegion to be initialized. >> * @owner: the object that tracks the region's reference count >> @@ -1464,8 +1466,8 @@ void *memory_region_get_ram_ptr(MemoryRegion *mr); >> >> /* memory_region_ram_resize: Resize a RAM region. >> * >> - * Only legal before guest might have detected the memory size: e.g. on >> - * incoming migration, or right after reset. >> + * Resizing RAM while migrating can result in the migration being canceled. >> + * Care has to be taken if the guest might have already detected the memory. >> * >> * @mr: a memory region created with @memory_region_init_resizeable_ram. >> * @newsize: the new size the region >> diff --git a/migration/migration.c b/migration/migration.c >> index 8fb68795dc..ac9751dbe5 100644 >> --- a/migration/migration.c >> +++ b/migration/migration.c >> @@ -175,13 +175,18 @@ void migration_object_init(void) >> } >> } >> >> +void migration_cancel(void) >> +{ >> + migrate_fd_cancel(current_migration); >> +} >> + >> void migration_shutdown(void) >> { >> /* >> * Cancel the current migration - that will (eventually) >> * stop the migration using this structure >> */ >> - migrate_fd_cancel(current_migration); >> + migration_cancel(); >> object_unref(OBJECT(current_migration)); >> } >> >> @@ -2019,7 +2024,7 @@ void qmp_migrate(const char *uri, bool has_blk, bool >> blk, >> >> void qmp_migrate_cancel(Error **errp) >> { >> - migrate_fd_cancel(migrate_get_current()); >> + migration_cancel(); >> } >> >> void qmp_migrate_continue(MigrationStatus state, Error **errp) >> diff --git a/migration/migration.h b/migration/migration.h >> index 8473ddfc88..79fd74afa5 100644 >> --- a/migration/migration.h >> +++ b/migration/migration.h >> @@ -343,5 +343,6 @@ int foreach_not_ignored_block(RAMBlockIterFunc func, >> void *opaque); >> void migration_make_urgent_request(void); >> void migration_consume_urgent_request(void); >> bool migration_rate_limit(void); >> +void migration_cancel(void); >> >> #endif >> diff --git a/migration/ram.c b/migration/ram.c >> index ed23ed1c7c..57f32011a3 100644 >> --- a/migration/ram.c >> +++ b/migration/ram.c >> @@ -52,6 +52,7 @@ >> #include "migration/colo.h" >> #include "block.h" >> #include "sysemu/sysemu.h" >> +#include "sysemu/runstate.h" >> #include "savevm.h" >> #include "qemu/iov.h" >> #include "multifd.h" >> @@ -3710,8 +3711,48 @@ static SaveVMHandlers savevm_ram_handlers = { >> .resume_prepare = ram_resume_prepare, >> }; >> >> +static void ram_mig_ram_block_resized(RAMBlockNotifier *n, void *host, >> + size_t old_size, size_t new_size) >> +{ >> + ram_addr_t offset; >> + Error *err = NULL; >> + RAMBlock *rb = qemu_ram_block_from_host(host, false, &offset); >> + >> + if (ramblock_is_ignored(rb)) { >> + return; >> + } >> + >> + /* >> + * Some resizes are triggered on the migration target by precopy code, >> + * when synchronizing RAM block sizes. In these cases, the VM is not >> + * running and migration is not idle. We have to ignore these resizes, >> + * as we only care about resizes during precopy on the migration source. >> + * This handler is always registered, so ignore when migration is idle. >> + */ >> + if (migration_is_idle() || !runstate_is_running() || >> + postcopy_is_running()) { >> + return; >> + } >> + >> + /* >> + * Precopy code cannot deal with the size of ram blocks changing at >> + * random points in time. We're still running on the source, abort >> + * the migration and continue running here. Make sure to wait until >> + * migration was canceled. >> + */ >> + error_setg(&err, "RAM block '%s' resized during precopy.", rb->idstr); >> + migrate_set_error(migrate_get_current(), err); >> + error_free(err); >> + migration_cancel(); >> +} >> + >> +static RAMBlockNotifier ram_mig_ram_notifier = { >> + .ram_block_resized = ram_mig_ram_block_resized, >> +}; >> + >> void ram_mig_init(void) >> { >> qemu_mutex_init(&XBZRLE.lock); >> register_savevm_live("ram", 0, 4, &savevm_ram_handlers, &ram_state); >> + ram_block_notifier_add(&ram_mig_ram_notifier); > > Can we avoid the question of the 'is_idle' checks by doing this > registration in save_setup/load_setup and unregistering in > save_cleanup/load_cleanup?
Well, I figured it out now :) migration_is_idle() is enough to handle it in this patch. > > That means if we land in the handler we know we're in either an incoming > or outgoing migration and then you just have to check which? Can save/load race with other QEMU code that might register/unregister notifiers? I want to avoid having to introduce locking just for that. -- Thanks, David / dhildenb