Re: [RFC PATCH for 8.1 5/6] vdpa: move CVQ isolation check to net_init_vhost_vdpa

[Stefano Garzarella <sgarzare@redhat.com>]

On Wed, Mar 22, 2023 at 07:04:03PM +0100, Eugenio Perez Martin wrote:
>On Wed, Mar 22, 2023 at 3:27 PM Stefano Garzarella <sgarzare@redhat.com> wrote:
>>
>> On Fri, Mar 17, 2023 at 03:55:41PM +0100, Eugenio Pérez wrote:
>> >Evaluating it at start time instead of initialization time may make the
>> >guest capable of dynamically adding or removing migration blockers.
>> >
>> >Also, moving to initialization reduces the number of ioctls in the
>> >migration, reducing failure possibilities.
>> >
>> >Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
>> >---
>> > net/vhost-vdpa.c | 200 +++++++++++++++++++++++++++++++++++++----------
>> > 1 file changed, 157 insertions(+), 43 deletions(-)
>> >
>> >diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
>> >index 4397c0d4b3..818a24fb0e 100644
>> >--- a/net/vhost-vdpa.c
>> >+++ b/net/vhost-vdpa.c
>> >@@ -43,6 +43,13 @@ typedef struct VhostVDPAState {
>> >
>> >     /* The device always have SVQ enabled */
>> >     bool always_svq;
>> >+
>> >+    /* The device can isolate CVQ in its own ASID if MQ is negotiated */
>> >+    bool cvq_isolated_mq;
>> >+
>> >+    /* The device can isolate CVQ in its own ASID if MQ is not negotiated */
>> >+    bool cvq_isolated;
>> >+
>>
>> I am not familiar with how CVQ works, so my question might be trivial
>> ;-) but why do we need to have 2 variables depending on F_MQ?
>>
>
>You're right, it is not specified anywhere in the series.
>
>Vring ASID / group management is based on vq indexes. CVQ is always
>the last queue, but its position depends on MQ. If it is not acked,
>cvq will always be queue #2. if it is acked, it will be
>net_config->max_virtqueue_pairs*2.
>
>Previously this was done at device start, so we always know if mq has
>been acked or not. But now we are moving to initialization, so we need
>to probe both configurations.
>
>Is that clearer now? I'll add to the patch description for sure.

Yes, thanks for the explanation!

Stefano