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

[Juan Quintela]

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

> ---
>  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++;