RE: [PATCH 1/6] Drivers: hv: vmbus: Fix handling of messages with transaction ID of zero

[Michael Kelley (LINUX)]

From: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx> Sent: Wednesday, April 6, 2022 9:30 PM
> 
> vmbus_request_addr() returns 0 (zero) if the transaction ID passed
> to as argument is 0.  This is unfortunate for two reasons: first,
> netvsc_send_completion() does not check for a NULL cmd_rqst (before
> dereferencing the corresponding NVSP message); second, 0 is a *valid*
> value of cmd_rqst in netvsc_send_tx_complete(), cf. the call of
> vmbus_sendpacket() in netvsc_send_pkt().
> 
> vmbus_request_addr() has included the code in question 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 by hv_storvsc.  Since
> hv_storvsc moved to a tag-based mechanism to generate and retrieve
> transaction IDs with commit bf5fd8cae3c8f ("scsi: storvsc: Use
> blk_mq_unique_tag() to generate requestIDs"), vmbus_request_addr()
> can be modified to return VMBUS_RQST_ERROR if the ID is 0.  This
> change solves the issues in hv_netvsc (and makes the handling of
> messages with transaction ID of 0 consistent with the semantics
> "the ID is not contained in the requestor/invalid ID").
> 
> vmbus_next_request_id(), vmbus_request_addr() should still reserve
> the ID of 0 for Hyper-V, because Hyper-V will "ignore" (not respond
> to) VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED packets/requests with
> transaction ID of 0 from the guest.
> 
> Fixes: bf5fd8cae3c8f ("scsi: storvsc: Use blk_mq_unique_tag() to generate requestIDs")
> Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx>
> ---
> The above hv_netvsc issues precede bf5fd8cae3c8f; however, these
> changes should not be backported to earlier commits since such a
> back-port would 'break' hv_storvsc.
> 
>  drivers/hv/channel.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
> index dc5c35210c16a..20fc8d50a0398 100644
> --- a/drivers/hv/channel.c
> +++ b/drivers/hv/channel.c
> @@ -1245,7 +1245,9 @@ u64 vmbus_next_request_id(struct vmbus_channel
> *channel, u64 rqst_addr)
> 
>  	/*
>  	 * Cannot return an ID of 0, which is reserved for an unsolicited
> -	 * message from Hyper-V.
> +	 * message from Hyper-V; Hyper-V does not acknowledge (respond to)
> +	 * VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED requests with ID of
> +	 * 0 sent by the guest.
>  	 */
>  	return current_id + 1;
>  }
> @@ -1270,7 +1272,7 @@ u64 vmbus_request_addr(struct vmbus_channel *channel,
> u64 trans_id)
> 
>  	/* Hyper-V can send an unsolicited message with ID of 0 */
>  	if (!trans_id)
> -		return trans_id;
> +		return VMBUS_RQST_ERROR;
> 
>  	spin_lock_irqsave(&rqstor->req_lock, flags);
> 
> --
> 2.25.1

Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>