[PATCH 5.17 492/772] Drivers: hv: vmbus: Fix handling of messages with transaction ID of zero

Greg Kroah-Hartman
2022-06-07T21:36:36Z

From: Andrea Parri (Microsoft) <parri.andrea@gmail.com>

[ Upstream commit 82cd4bacff88a11e36f143e2cb950174b09c86c3 ]

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@gmail.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20220419122325.10078-2-parri.andrea@gmail.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 dc5c35210c16..20fc8d50a039 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);

--
2.35.1