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virtio-mem: Support "x-ignore-shared" migration 

To achieve desired "x-ignore-shared" functionality, we should not
discard all RAM when realizing the device and not mess with
preallocation/postcopy when loading device state. In essence, we should
not touch RAM content.

As "x-ignore-shared" gets set after realizing the device, we cannot
rely on that. Let's simply skip discarding of RAM on incoming migration.
Note that virtio_mem_post_load() will call
virtio_mem_restore_unplugged() -- unless "x-ignore-shared" is set. So
once migration finished we'll have a consistent state.

The initial system reset will also not discard any RAM, because
virtio_mem_unplug_all() will not call virtio_mem_unplug_all() when no
memory is plugged (which is the case before loading the device state).

Note that something like VM templating -- see commit b17fbbe55c
("migration: allow private destination ram with x-ignore-shared") -- is
currently incompatible with virtio-mem and ram_block_discard_range() will
warn in case a private file mapping is supplied by virtio-mem.

For VM templating with virtio-mem, it makes more sense to either
(a) Create the template without the virtio-mem device and hotplug a
    virtio-mem device to the new VM instances using proper own memory
    backend.
(b) Use a virtio-mem device that doesn't provide any memory in the
    template (requested-size=0) and use private anonymous memory.

Message-ID: <20230706075612.67404-5-david@redhat.com>
Tested-by: Mario Casquero <mcasquer@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
master
David Hildenbrand 2023-07-06 09:56:09 +02:00
parent f161c88a03
commit b01fd4b67a
1 changed files with 38 additions and 9 deletions
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47
hw/virtio/virtio-mem.c
View File

@ -18,6 +18,7 @@
#include "sysemu/numa.h"
#include "sysemu/sysemu.h"
#include "sysemu/reset.h"
#include "sysemu/runstate.h"
#include "hw/virtio/virtio.h"
#include "hw/virtio/virtio-bus.h"
#include "hw/virtio/virtio-mem.h"
@ -901,11 +902,23 @@ static void virtio_mem_device_realize(DeviceState *dev, Error **errp)
return;
}
ret = ram_block_discard_range(rb, 0, qemu_ram_get_used_length(rb));
if (ret) {
error_setg_errno(errp, -ret, "Unexpected error discarding RAM");
ram_block_coordinated_discard_require(false);
return;
/*
* We don't know at this point whether shared RAM is migrated using
* QEMU or migrated using the file content. "x-ignore-shared" will be
* configured after realizing the device. So in case we have an
* incoming migration, simply always skip the discard step.
*
* Otherwise, make sure that we start with a clean slate: either the
* memory backend might get reused or the shared file might still have
* memory allocated.
*/
if (!runstate_check(RUN_STATE_INMIGRATE)) {
ret = ram_block_discard_range(rb, 0, qemu_ram_get_used_length(rb));
if (ret) {
error_setg_errno(errp, -ret, "Unexpected error discarding RAM");
ram_block_coordinated_discard_require(false);
return;
}
}
virtio_mem_resize_usable_region(vmem, vmem->requested_size, true);
@ -977,10 +990,6 @@ static int virtio_mem_post_load(void *opaque, int version_id)
RamDiscardListener *rdl;
int ret;
if (vmem->prealloc && !vmem->early_migration) {
warn_report("Proper preallocation with migration requires a newer QEMU machine");
}
/*
* We started out with all memory discarded and our memory region is mapped
* into an address space. Replay, now that we updated the bitmap.
@ -993,6 +1002,18 @@ static int virtio_mem_post_load(void *opaque, int version_id)
}
}
/*
* If shared RAM is migrated using the file content and not using QEMU,
* don't mess with preallocation and postcopy.
*/
if (migrate_ram_is_ignored(vmem->memdev->mr.ram_block)) {
return 0;
}
if (vmem->prealloc && !vmem->early_migration) {
warn_report("Proper preallocation with migration requires a newer QEMU machine");
}
if (migration_in_incoming_postcopy()) {
return 0;
}
@ -1025,6 +1046,14 @@ static int virtio_mem_post_load_early(void *opaque, int version_id)
return 0;
}
/*
* If shared RAM is migrated using the file content and not using QEMU,
* don't mess with preallocation and postcopy.
*/
if (migrate_ram_is_ignored(rb)) {
return 0;
}
/*
* We restored the bitmap and verified that the basic properties
* match on source and destination, so we can go ahead and preallocate