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Re: [Qemu-devel] [PATCH v1] migration/ram.c: do not set 'postcopy_runnin
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH v1] migration/ram.c: do not set 'postcopy_running' in POSTCOPY_INCOMING_END |
Date: |
Tue, 21 Nov 2017 18:54:57 +0000 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
* 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:
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