Re: [PATCH v1 1/1] migration: Avoid false-positive on non-supported scenarios for zero-copy-send

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Leonardo Bras (leobras@redhat.com) wrote:
> Migration with zero-copy-send currently has it's limitations, as it can't
> be used with TLS nor any kind of compression. In such scenarios, it should
> output errors during parameter / capability setting.
> 
> But currently there are some ways of setting this not-supported scenarios
> without printing the error message:
> 
> !) For 'compression' capability, it works by enabling it together with
> zero-copy-send. This happens because the validity test for zero-copy uses
> the helper unction migrate_use_compression(), which check for compression
> presence in s->enabled_capabilities[MIGRATION_CAPABILITY_COMPRESS].
> 
> The point here is: the validity test happens before the capability gets
> enabled. If all of them get enabled together, this test will not return
> error.
> 
> In order to fix that, replace migrate_use_compression() by directly testing
> the cap_list parameter migrate_caps_check().
> 
> 2) For features enabled by parameters such as TLS & 'multifd_compression',
> there was also a possibility of setting non-supported scenarios: setting
> zero-copy-send first, then setting the unsupported parameter.
> 
> In order to fix that, also add a check for parameters conflicting with
> zero-copy-send on migrate_params_check().
> 
> 3) XBZRLE is also a compression capability, so it makes sense to also add
> it to the list of capabilities which are not supported with zero-copy-send.
> 
> Fixes: 1abaec9a1b2c ("migration: Change zero_copy_send from migration parameter to migration capability")
> Signed-off-by: Leonardo Bras <leobras@redhat.com>

Yeh, it's unusual in that you need to check both the capabilities and
parameters; where as we have the inidividual 'caps_check' and
'params_check'.


Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> ---
>  migration/migration.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/migration/migration.c b/migration/migration.c
> index 78f5057373..c6260e54bf 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -1274,7 +1274,9 @@ static bool migrate_caps_check(bool *cap_list,
>  #ifdef CONFIG_LINUX
>      if (cap_list[MIGRATION_CAPABILITY_ZERO_COPY_SEND] &&
>          (!cap_list[MIGRATION_CAPABILITY_MULTIFD] ||
> -         migrate_use_compression() ||
> +         cap_list[MIGRATION_CAPABILITY_COMPRESS] ||
> +         cap_list[MIGRATION_CAPABILITY_XBZRLE] ||
> +         migrate_multifd_compression() ||
>           migrate_use_tls())) {
>          error_setg(errp,
>                     "Zero copy only available for non-compressed non-TLS multifd migration");
> @@ -1511,6 +1513,17 @@ static bool migrate_params_check(MigrationParameters *params, Error **errp)
>          error_prepend(errp, "Invalid mapping given for block-bitmap-mapping: ");
>          return false;
>      }
> +
> +#ifdef CONFIG_LINUX
> +    if (migrate_use_zero_copy_send() &&
> +        ((params->has_multifd_compression && params->multifd_compression) ||
> +         (params->has_tls_creds && params->tls_creds && *params->tls_creds))) {
> +        error_setg(errp,
> +                   "Zero copy only available for non-compressed non-TLS multifd migration");
> +        return false;
> +    }
> +#endif
> +
>      return true;
>  }
>  
> -- 
> 2.37.1
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK