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    Subject[PATCH 5.15 419/667] Drivers: hv: vmbus: Fix handling of messages with transaction ID of zero
    Date
    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 f3761c73b074..6b967bb38690 100644
    --- a/drivers/hv/channel.c
    +++ b/drivers/hv/channel.c
    @@ -1221,7 +1221,9 @@ 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;
    }
    @@ -1246,7 +1248,7 @@ 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


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