On 20.06.23 15:06, Michael S. Tsirkin wrote:
On Tue, Jun 20, 2023 at 03:03:54PM +0200, David Hildenbrand wrote:
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 b17fbbe55cba
("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.
Signed-off-by: David Hildenbrand <da...@redhat.com>
---
hw/virtio/virtio-mem.c | 47 ++++++++++++++++++++++++++++++++++--------
1 file changed, 38 insertions(+), 9 deletions(-)
diff --git a/hw/virtio/virtio-mem.c b/hw/virtio/virtio-mem.c
index 9f6169af32..b013dfbaf0 100644
--- a/hw/virtio/virtio-mem.c
+++ b/hw/virtio/virtio-mem.c
@@ -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-access.h"
@@ -886,11 +887,23 @@ 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
+ * configurated
configurated == configured?
Thanks!
--
Cheers,
David / dhildenb
