Re: [Qemu-devel] [PATCH v1] migration/ram.c: do not set 'postcopy_running' in POSTCOPY_INCOMING_END

[Juan Quintela]

"Dr. David Alan Gilbert" <address@hidden> wrote:
> * Juan Quintela (address@hidden) wrote:
>> Daniel Henrique Barboza <address@hidden> 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 <address@hidden>
>> 
>> Reviewed-by: Juan Quintela <address@hidden>
>> 
>> queued
>
> Wrong version; v3 is:

My bad, sorry.  Got a new one.

No clue why search on my INBOX didn't found this version.

compiling a new pull request.

>
> http://lists.nongnu.org/archive/html/qemu-devel/2017-11/msg03188.html
>
> Dave
>
>> > ---
>> >  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++;
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK