From: Phil Dennis-Jordan Date: Fri, 13 Dec 2024 16:06:14 +0000 (+0100) Subject: hw/usb/hcd-xhci-pci: Use modulo to select MSI vector as per spec X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=bb5b7fced6b5d3334ab20702fc846e47bb1fb731;p=qemu.git hw/usb/hcd-xhci-pci: Use modulo to select MSI vector as per spec QEMU would crash with a failed assertion if the XHCI controller attempted to raise the interrupt on an interrupter corresponding to a MSI vector with a higher index than the highest configured for the device by the guest driver. This behaviour is correct on the MSI/PCI side: per PCI 3.0 spec, devices must ensure they do not send MSI notifications for vectors beyond the range of those allocated by the system/driver software. Unlike MSI-X, there is no generic way for handling aliasing in the case of fewer allocated vectors than requested, so the specifics are up to device implementors. (Section 6.8.3.4. "Sending Messages") 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. This makes the device work correctly in MSI mode with macOS's XHCI driver, which only allocates a single vector. Signed-off-by: Phil Dennis-Jordan Reviewed-by: Philippe Mathieu-Daudé Message-ID: <20250112210056.16658-2-phil@philjordan.eu> Signed-off-by: Philippe Mathieu-Daudé --- diff --git a/hw/usb/hcd-xhci-pci.c b/hw/usb/hcd-xhci-pci.c index a069b42338..49642aab58 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; }