On 21.02.20 10:18, David Hildenbrand wrote: > On 20.02.20 21:17, Peter Xu wrote: >> On Thu, Feb 20, 2020 at 04:16:02PM +0100, David Hildenbrand wrote: >>> On 19.02.20 17:17, David Hildenbrand 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() || >> >> So I noticed that I mis-misread the code after chat with Dave... >> >> migration_is_idle() should only return false if on the source and only >> if during migration. Destination should still return true for that >> (destination VM reads state from MigrationIncomingState.state >> instead). >> >> With that, I think we can drop the confusing !runstate_is_running() >> check because migration_is_idle() will cover that (and touch up the >> comment too)? > > So, we want to cancel migration whenever we are on the source and we are > migrating (postcopy). Resizing will only happen while the VM is running > on the source once we're migrating. > > So you're saying that > > if (migration_is_idle() || postcopy_is_running()) { > return: > } > > is enough. Will migration_is_idle() always return true on the > destination (I remember something different, but might be *I* misread > the code)? > > Then this would distill down to > > if (migration_is_idle()) { > return: > } > > Which would be nice.
... but looking at process_incoming_migration_co(), we'll set the state to MIGRATION_STATUS_ACTIVE right at the start. So dropping postcopy_is_running() would be wrong and dropping !runstate_is_running() would be wrong as well right now. What we actually want is if (!migration_outgoing()) { return; } Any experts? -- Thanks, David / dhildenb