linux-kernel - [PATCH] xhci: Fix Link TRB DMA in command ring stopped completion event

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Message-ID: <20241018195953.12315-1-quic_faisalh@quicinc.com>
Date: Sat, 19 Oct 2024 01:29:53 +0530
From: Faisal Hassan <quic_faisalh@...cinc.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mathias Nyman
	<mathias.nyman@...el.com>
CC: <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Faisal Hassan
	<quic_faisalh@...cinc.com>, <stable@...r.kernel.org>
Subject: [PATCH] xhci: Fix Link TRB DMA in command ring stopped completion event

During the aborting of a command, the software receives a command
completion event for the command ring stopped, with the TRB pointing
to the next TRB after the aborted command.

If the command we abort is located just before the Link TRB in the
command ring, then during the 'command ring stopped' completion event,
the xHC gives the Link TRB in the event's cmd DMA, which causes a
mismatch in handling command completion event.

To handle this situation, an additional check has been added to ignore
the mismatch error and continue the operation.

Cc: stable@...r.kernel.org
Signed-off-by: Faisal Hassan <quic_faisalh@...cinc.com>
---
 drivers/usb/host/xhci-ring.c | 38 +++++++++++++++++++++++++++++++++---
 1 file changed, 35 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index b2950c35c740..43926c378df9 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -126,6 +126,32 @@ static void inc_td_cnt(struct urb *urb)
 	urb_priv->num_tds_done++;
 }
 
+/*
+ * Return true if the DMA is pointing to a Link TRB in the ring;
+ * otherwise, return false.
+ */
+static bool is_dma_link_trb(struct xhci_ring *ring, dma_addr_t dma)
+{
+	struct xhci_segment *seg;
+	union xhci_trb *trb;
+	dma_addr_t trb_dma;
+	int i;
+
+	seg = ring->first_seg;
+	do {
+		for (i = 0; i < TRBS_PER_SEGMENT; i++) {
+			trb = &seg->trbs[i];
+			trb_dma = seg->dma + (i * sizeof(union xhci_trb));
+
+			if (trb_is_link(trb) && trb_dma == dma)
+				return true;
+		}
+		seg = seg->next;
+	} while (seg != ring->first_seg);
+
+	return false;
+}
+
 static void trb_to_noop(union xhci_trb *trb, u32 noop_type)
 {
 	if (trb_is_link(trb)) {
@@ -1718,13 +1744,21 @@ static void handle_cmd_completion(struct xhci_hcd *xhci,
 
 	trace_xhci_handle_command(xhci->cmd_ring, &cmd_trb->generic);
 
+	cmd_comp_code = GET_COMP_CODE(le32_to_cpu(event->status));
 	cmd_dequeue_dma = xhci_trb_virt_to_dma(xhci->cmd_ring->deq_seg,
 			cmd_trb);
 	/*
 	 * Check whether the completion event is for our internal kept
 	 * command.
+	 * For the 'command ring stopped' completion event, there is a
+	 * risk of a mismatch in dequeue pointers if we abort the command
+	 * just before the link TRB in the command ring. In this scenario,
+	 * the cmd_dma in the event would point to a link TRB, while the
+	 * software dequeue pointer circles back to the start.
 	 */
-	if (!cmd_dequeue_dma || cmd_dma != (u64)cmd_dequeue_dma) {
+	if ((!cmd_dequeue_dma || cmd_dma != (u64)cmd_dequeue_dma) &&
+	    !(cmd_comp_code == COMP_COMMAND_RING_STOPPED &&
+	      is_dma_link_trb(xhci->cmd_ring, cmd_dma))) {
 		xhci_warn(xhci,
 			  "ERROR mismatched command completion event\n");
 		return;
@@ -1734,8 +1768,6 @@ static void handle_cmd_completion(struct xhci_hcd *xhci,
 
 	cancel_delayed_work(&xhci->cmd_timer);
 
-	cmd_comp_code = GET_COMP_CODE(le32_to_cpu(event->status));
-
 	/* If CMD ring stopped we own the trbs between enqueue and dequeue */
 	if (cmd_comp_code == COMP_COMMAND_RING_STOPPED) {
 		complete_all(&xhci->cmd_ring_stop_completion);
-- 
2.17.1