On 21.02.20 11:10, David Hildenbrand wrote: > 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? >
Lol, man this code is confusing. So, migration_is_idle() really only checks current_migration, not current_incoming. I didn't expect to be knees deep in migration code at this point ... if (migration_is_idle()) { return: } works. Thanks! -- Thanks, David / dhildenb