Limits should be big enough that normal guest should not hit it.
Add a tracepoint to log them, just in case.  Also, while being
at it, log the existing link trb limit too.

Reported-by: 李强 <address@hidden>
Signed-off-by: Gerd Hoffmann <address@hidden>
---
 hw/usb/hcd-xhci.c   | 15 ++++++++++++++-
 hw/usb/trace-events |  1 +
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/hw/usb/hcd-xhci.c b/hw/usb/hcd-xhci.c
index fbf8a8b..28dd2f2 100644
--- a/hw/usb/hcd-xhci.c
+++ b/hw/usb/hcd-xhci.c
@@ -51,6 +51,8 @@
 #define EV_QUEUE (((3 * 24) + 16) * MAXSLOTS)
 
 #define TRB_LINK_LIMIT  4
+#define COMMAND_LIMIT   256
+#define TRANSFER_LIMIT  256
 
 #define LEN_CAP         0x40
 #define LEN_OPER        (0x400 + 0x10 * MAXPORTS)
@@ -943,6 +945,7 @@ static TRBType xhci_ring_fetch(XHCIState *xhci, XHCIRing *ring, XHCITRB *trb,
             return type;
         } else {
             if (++link_cnt > TRB_LINK_LIMIT) {
+                trace_usb_xhci_enforced_limit("trb-link");
                 return 0;
             }
             ring->dequeue = xhci_mask64(trb->parameter);
@@ -2060,6 +2063,7 @@ static void xhci_kick_epctx(XHCIEPContext *epctx, unsigned int streamid)
     XHCIRing *ring;
     USBEndpoint *ep = NULL;
     uint64_t mfindex;
+    unsigned int count = 0;
     int length;
     int i;
 
@@ -2172,6 +2176,10 @@ static void xhci_kick_epctx(XHCIEPContext *epctx, unsigned int streamid)
             epctx->retry = xfer;
             break;
         }
+        if (count++ > TRANSFER_LIMIT) {
+            trace_usb_xhci_enforced_limit("transfers");
+            break;
+        }
     }
     epctx->kick_active--;
 
@@ -2618,7 +2626,7 @@ static void xhci_process_commands(XHCIState *xhci)
     TRBType type;
     XHCIEvent event = {ER_COMMAND_COMPLETE, CC_SUCCESS};
     dma_addr_t addr;
-    unsigned int i, slotid = 0;
+    unsigned int i, slotid = 0, count = 0;
 
     DPRINTF("xhci_process_commands()\n");
     if (!xhci_running(xhci)) {
@@ -2735,6 +2743,11 @@ static void xhci_process_commands(XHCIState *xhci)
         }
         event.slotid = slotid;
         xhci_event(xhci, &event, 0);
+
+        if (count++ > COMMAND_LIMIT) {
+            trace_usb_xhci_enforced_limit("commands");
+            return;
+        }
     }
 }
 
diff --git a/hw/usb/trace-events b/hw/usb/trace-events
index fdd1d29..0c323d4 100644
--- a/hw/usb/trace-events
+++ b/hw/usb/trace-events
@@ -174,6 +174,7 @@ usb_xhci_xfer_retry(void *xfer) "%p"
 usb_xhci_xfer_success(void *xfer, uint32_t bytes) "%p: len %d"
 usb_xhci_xfer_error(void *xfer, uint32_t ret) "%p: ret %d"
 usb_xhci_unimplemented(const char *item, int nr) "%s (0x%x)"
+usb_xhci_enforced_limit(const char *item) "%s"
 
 # hw/usb/desc.c
 usb_desc_device(int addr, int len, int ret) "dev %d query device, len %d, ret %d"
-- 
1.8.3.1