Daniel Henrique Barboza <danie...@linux.vnet.ibm.com> wrote:
> When migrating a VM with 'migrate_set_capability postcopy-ram on'
> a postcopy_state is set during the process, ending up with the
> state POSTCOPY_INCOMING_END when the migration is over. This
> postcopy_state is taken into account inside ram_load to check
> how it will load the memory pages. This same ram_load is called when
> in a loadvm command.
>
> Inside ram_load, the logic to see if we're at postcopy_running state
> is:
>
> postcopy_running = postcopy_state_get() >= POSTCOPY_INCOMING_LISTENING
>
> postcopy_state_get() returns this enum type:
>
> typedef enum {
> POSTCOPY_INCOMING_NONE = 0,
> POSTCOPY_INCOMING_ADVISE,
> POSTCOPY_INCOMING_DISCARD,
> POSTCOPY_INCOMING_LISTENING,
> POSTCOPY_INCOMING_RUNNING,
> POSTCOPY_INCOMING_END
> } PostcopyState;
>
> In the case where ram_load is executed and postcopy_state is
> POSTCOPY_INCOMING_END, postcopy_running will be set to 'true' and
> ram_load will behave like a postcopy is in progress. This scenario isn't
> achievable in a migration but it is reproducible when executing
> savevm/loadvm after migrating with 'postcopy-ram on', causing loadvm
> to fail with Error -22:
>
> Source:
>
> (qemu) migrate_set_capability postcopy-ram on
> (qemu) migrate tcp:127.0.0.1:4444
>
> Dest:
>
> (qemu) migrate_set_capability postcopy-ram on
> (qemu)
> ubuntu1704-intel login:
> Ubuntu 17.04 ubuntu1704-intel ttyS0
>
> ubuntu1704-intel login: (qemu)
> (qemu) savevm test1
> (qemu) loadvm test1
> Unknown combination of migration flags: 0x4 (postcopy mode)
> error while loading state for instance 0x0 of device 'ram'
> Error -22 while loading VM state
> (qemu)
>
> This patch fixes this problem by changing a bit the semantics
> of postcopy_running inside ram_load, verifying first if
> we're not in the POSTCOPY_INCOMING_END state. In this case,
> postcopy_running is set to 'false'.
>
> Signed-off-by: Daniel Henrique Barboza <danie...@linux.vnet.ibm.com>
Reviewed-by: Juan Quintela <quint...@redhat.com>
queued
> ---
> migration/ram.c | 22 +++++++++++++++-------
> 1 file changed, 15 insertions(+), 7 deletions(-)
>
> diff --git a/migration/ram.c b/migration/ram.c
> index 8620aa400a..43ed719668 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -2803,13 +2803,21 @@ static int ram_load(QEMUFile *f, void *opaque, int
> version_id)
> int flags = 0, ret = 0, invalid_flags = 0;
> static uint64_t seq_iter;
> int len = 0;
> - /*
> - * If system is running in postcopy mode, page inserts to host memory
> must
> - * be atomic
> - */
> - bool postcopy_running = postcopy_state_get() >=
> POSTCOPY_INCOMING_LISTENING;
> - /* ADVISE is earlier, it shows the source has the postcopy capability on
> */
> - bool postcopy_advised = postcopy_state_get() >= POSTCOPY_INCOMING_ADVISE;
> + bool postcopy_advised = false, postcopy_running = false;
> + uint8_t postcopy_state = postcopy_state_get();
> +
> + if (postcopy_state != POSTCOPY_INCOMING_END) {
> + /*
> + * If system is running in postcopy mode, page inserts to host memory
> + * must be atomic
> + */
> + postcopy_running = postcopy_state >= POSTCOPY_INCOMING_LISTENING;
> +
> + /* ADVISE is earlier, it shows the source has the postcopy
> + * capability on
> + */
> + postcopy_advised = postcopy_state >= POSTCOPY_INCOMING_ADVISE;
> + }
>
> seq_iter++;
