QEMU would crash with a failed assertion if the XHCI controller
attempted to raise the interrupt on a higher vector than the
highest configured for the device by the guest driver.

It turns out the XHCI spec (Implementation Note in section 4.17,
"Interrupters") requires that the host controller signal the MSI
vector with the number computed by taking the interrupter number
modulo the number of enabled MSI vectors.

This change introduces that modulo calculation, fixing the
failed assertion and making the device work correctly in MSI mode
with macOS's XHCI driver.

Signed-off-by: Phil Dennis-Jordan <phil@philjordan.eu>
---

v2:

 * Switch to modulo arithmetic for MSI vector number rather than dropping,
   as per spec.

 hw/usb/hcd-xhci-pci.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/hw/usb/hcd-xhci-pci.c b/hw/usb/hcd-xhci-pci.c
index a039f5778a6..516e6909d20 100644
--- a/hw/usb/hcd-xhci-pci.c
+++ b/hw/usb/hcd-xhci-pci.c
@@ -74,6 +74,7 @@ static bool xhci_pci_intr_raise(XHCIState *xhci, int n, bool level)
     }
 
     if (msi_enabled(pci_dev) && level) {
+        n %= msi_nr_vectors_allocated(pci_dev);
         msi_notify(pci_dev, n);
         return true;
     }
-- 
2.39.5 (Apple Git-154)