From 4a3538e6f287b383daa82410769cec1b79e6df02 Mon Sep 17 00:00:00 2001 From: Phil Dennis-Jordan Date: Fri, 13 Dec 2024 17:06:14 +0100 Subject: [PATCH] hw/usb/hcd-xhci-pci: Use modulo to select MSI vector as per spec MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 (cherry picked from commit bb5b7fced6b5d3334ab20702fc846e47bb1fb731) Signed-off-by: Michael Tokarev --- 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 a039f5778a..516e6909d2 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; }