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Re: [PATCH v1 05/13] migrate/ram: Handle RAM block resizes during precop
From: |
David Hildenbrand |
Subject: |
Re: [PATCH v1 05/13] migrate/ram: Handle RAM block resizes during precopy |
Date: |
Fri, 21 Feb 2020 16:18:44 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 |
On 21.02.20 16:14, Dr. David Alan Gilbert wrote:
> * David Hildenbrand (address@hidden) 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" <address@hidden>
>> Cc: Juan Quintela <address@hidden>
>> Cc: Eduardo Habkost <address@hidden>
>> Cc: Paolo Bonzini <address@hidden>
>> Cc: Igor Mammedov <address@hidden>
>> Cc: "Michael S. Tsirkin" <address@hidden>
>> Cc: Richard Henderson <address@hidden>
>> Cc: Shannon Zhao <address@hidden>
>> Cc: Alex Bennée <address@hidden>
>> Cc: Peter Xu <address@hidden>
>> Signed-off-by: David Hildenbrand <address@hidden>
>> ---
>> 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
- Re: [PATCH v1 04/13] numa: Make all callbacks of ram block notifiers optional, (continued)
Re: [PATCH v1 05/13] migrate/ram: Handle RAM block resizes during precopy, Dr. David Alan Gilbert, 2020/02/21
[PATCH v1 08/13] migrate/ram: Simplify host page handling in ram_load_postcopy(), David Hildenbrand, 2020/02/19
[PATCH v1 09/13] migrate/ram: Consolidate variable reset after placement in ram_load_postcopy(), David Hildenbrand, 2020/02/19
[PATCH v1 07/13] migrate/ram: Get rid of "place_source" in ram_load_postcopy(), David Hildenbrand, 2020/02/19
Re: [PATCH v1 07/13] migrate/ram: Get rid of "place_source" in ram_load_postcopy(), David Hildenbrand, 2020/02/20