On Mon, Mar 28, 2022 at 04:42:41PM +0200, Andrea Parri (Microsoft) wrote:
> vmbus_requestor has included code for handling unsolicited messages
> since its introduction with commit e8b7db38449ac ("Drivers: hv: vmbus:
> Add vmbus_requestor data structure for VMBus hardening"); such code was
> motivated by the early use of vmbus_requestor from storvsc. Since
> storvsc moved to a tag-based mechanism to generate/retrieve request IDs
> with commit bf5fd8cae3c8f ("scsi: storvsc: Use blk_mq_unique_tag() to
> generate requestIDs"), the special handling of unsolicited messages in
> vmbus_requestor is not useful and can be removed.
As it turns out, this is not quite right. In particular...
> @@ -1243,11 +1243,7 @@ u64 vmbus_next_request_id(struct vmbus_channel *channel, u64 rqst_addr)
>
> spin_unlock_irqrestore(&rqstor->req_lock, flags);
>
> - /*
> - * Cannot return an ID of 0, which is reserved for an unsolicited
> - * message from Hyper-V.
> - */
> - return current_id + 1;
> + return current_id;
Hyper-V treats requests with ID of 0 as "non-transactional" and it does
not respond to such requests.
> @@ -1268,15 +1264,8 @@ u64 vmbus_request_addr(struct vmbus_channel *channel, u64 trans_id)
> if (!channel->rqstor_size)
> return VMBUS_NO_RQSTOR;
>
> - /* Hyper-V can send an unsolicited message with ID of 0 */
> - if (!trans_id)
> - return trans_id;
This remains problematic: I will elaborate and propose some solution in
the next iteration (to be sent shortly).
Thanks,
Andrea
> -
> spin_lock_irqsave(&rqstor->req_lock, flags);
>
> - /* Data corresponding to trans_id is stored at trans_id - 1 */
> - trans_id--;
> -
> /* Invalid trans_id */
> if (trans_id >= rqstor->size || !test_bit(trans_id, rqstor->req_bitmap)) {
> spin_unlock_irqrestore(&rqstor->req_lock, flags);
