RE: [PATCH 2/2] PCI: hv: Fix synchronization between channel callback and hv_pci_bus_exit()

["Michael Kelley (LINUX)" <mikelley@microsoft.com>]

From: Andrea Parri (Microsoft) <parri.andrea@gmail.com> Sent: Wednesday, May 4, 2022 5:51 AM
> 
> [ Similarly to commit a765ed47e4516 ("PCI: hv: Fix synchronization
>   between channel callback and hv_compose_msi_msg()"): ]
> 
> The (on-stack) teardown packet becomes invalid once the completion
> timeout in hv_pci_bus_exit() has expired and hv_pci_bus_exit() has
> returned.  Prevent the channel callback from accessing the invalid
> packet by removing the ID associated to such packet from the VMbus
> requestor in hv_pci_bus_exit().
> 
> Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
> ---
>  drivers/pci/controller/pci-hyperv.c | 26 +++++++++++++++++++-------
>  1 file changed, 19 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> index 9a3e17b682eb7..db4b3f86726b2 100644
> --- a/drivers/pci/controller/pci-hyperv.c
> +++ b/drivers/pci/controller/pci-hyperv.c
> @@ -3620,6 +3620,7 @@ static int hv_pci_probe(struct hv_device *hdev,
>  static int hv_pci_bus_exit(struct hv_device *hdev, bool keep_devs)
>  {
>  	struct hv_pcibus_device *hbus = hv_get_drvdata(hdev);
> +	struct vmbus_channel *chan = hdev->channel;
>  	struct {
>  		struct pci_packet teardown_packet;
>  		u8 buffer[sizeof(struct pci_message)];
> @@ -3627,13 +3628,14 @@ static int hv_pci_bus_exit(struct hv_device *hdev, bool
> keep_devs)
>  	struct hv_pci_compl comp_pkt;
>  	struct hv_pci_dev *hpdev, *tmp;
>  	unsigned long flags;
> +	u64 trans_id;
>  	int ret;
> 
>  	/*
>  	 * After the host sends the RESCIND_CHANNEL message, it doesn't
>  	 * access the per-channel ringbuffer any longer.
>  	 */
> -	if (hdev->channel->rescind)
> +	if (chan->rescind)
>  		return 0;
> 
>  	if (!keep_devs) {
> @@ -3670,16 +3672,26 @@ static int hv_pci_bus_exit(struct hv_device *hdev, bool
> keep_devs)
>  	pkt.teardown_packet.compl_ctxt = &comp_pkt;
>  	pkt.teardown_packet.message[0].type = PCI_BUS_D0EXIT;
> 
> -	ret = vmbus_sendpacket(hdev->channel, &pkt.teardown_packet.message,
> -			       sizeof(struct pci_message),
> -			       (unsigned long)&pkt.teardown_packet,
> -			       VM_PKT_DATA_INBAND,
> -			       VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
> +	ret = vmbus_sendpacket_getid(chan, &pkt.teardown_packet.message,
> +				     sizeof(struct pci_message),
> +				     (unsigned long)&pkt.teardown_packet,
> +				     &trans_id, VM_PKT_DATA_INBAND,
> +
> VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED);
>  	if (ret)
>  		return ret;
> 
> -	if (wait_for_completion_timeout(&comp_pkt.host_event, 10 * HZ) == 0)
> +	if (wait_for_completion_timeout(&comp_pkt.host_event, 10 * HZ) == 0) {
> +		/*
> +		 * The completion packet on the stack becomes invalid after
> +		 * 'return'; remove the ID from the VMbus requestor if the
> +		 * identifier is still mapped to/associated with the packet.
> +		 *
> +		 * Cf. hv_pci_onchannelcallback().
> +		 */
> +		vmbus_request_addr_match(chan, trans_id,
> +					 (unsigned long)&pkt.teardown_packet);
>  		return -ETIMEDOUT;
> +	}
> 
>  	return 0;
>  }
> --
> 2.25.1

Reviewed-by: Michael Kelley <mikelley@microsoft.com>