---
src/util/virpci.c | 106 +++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 99 insertions(+), 7 deletions(-)
diff --git a/src/util/virpci.c b/src/util/virpci.c
index 2348a98003..f2ce24e6aa 100644
--- a/src/util/virpci.c
+++ b/src/util/virpci.c
@@ -1081,6 +1081,81 @@ virPCIDeviceInit(virPCIDevice *dev, int cfgfd)
return 0;
}
+/*
+ * Check if a PCI device is directly attached to a root bus (no parent bridge).
+ *
+ * Modern systems like Intel Arrow Lake (Core Ultra 200) can have multiple
+ * root buses (e.g., bus 0x00 for CPU devices and bus 0x80 for PCH devices).
+ * We detect root bus attachment by examining the sysfs topology: a device
+ * is on a root bus if its sysfs path is a direct child of a pciXXXX:YY
+ * directory (e.g., /sys/devices/pci0000:80/0000:80:14.0).
+ *
+ * Returns 1 if on root bus, 0 if not, -1 on error.
+ */
+static int
+virPCIDeviceIsOnRootBus(virPCIDevice *dev)
+{
+ unsigned int domain, bus;
+ g_autofree char *devPath = NULL;
+ g_autofree char *realPath = NULL;
+ g_autofree char *parentDir = NULL;
+ const char *parentName;
+
+ /* Get the sysfs symlink path for this device */
+ devPath = g_strdup_printf(PCI_SYSFS "devices/%s", dev->name);
+
+ /* Resolve the symlink to get the real path in /sys/devices/... */
+ if (virFileResolveLink(devPath, &realPath) < 0) {
+ VIR_DEBUG("%s %s: failed to resolve sysfs path %s",
+ dev->id, dev->name, devPath);
+ return -1;
+ }
+
+ parentDir = g_path_get_dirname(realPath);
+ if (!parentDir)
+ return -1;
+
+ parentName = strrchr(parentDir, '/');
+ if (!parentName)
+ return -1;
+ parentName++; // skip the '/'
+
+ /*
+ * Detect root bus by parsing the parent directory name using sscanf.
+ *
+ * PCI root buses in sysfs follow the naming convention:
+ * pci<domain>:<bus>
+ *
+ * - <domain>: number (0000-ffff, hex)
+ * - <bus>: number within the domain (00-ff, hex)
+ *
+ * This format is defined in:
+ * https://www.kernel.org/doc/html/latest/PCI/sysfs-pci.html
+ *
+ * Examples from Intel Arrow Lake systems:
+ * - pci0000:00 (CPU root bus)
+ * - pci0000:80 (PCH root bus - the problematic case on Arrow Lake)
+ *
+ * sscanf pattern "pci%x:%x" matches:
+ * - "pci" : literal prefix
+ * - "%x" : hex domain (stops at ':')
+ * - ":" : literal separator
+ * - "%x" : hex bus (must reach end of string)
+ *
+ * Returns 2 if both domain and bus were successfully parsed,
+ * confirming the device is a direct child of a root bus.
+ */
+ if (sscanf(parentName, "pci%x:%x", &domain, &bus) == 2) {
+ VIR_DEBUG("%s %s: device is on root bus (parent=%s)",
+ dev->id, dev->name, parentName);
+ return 1;
+ }
+
+ VIR_DEBUG("%s %s: device is not on root bus (parent=%s)",
+ dev->id, dev->name, parentName);
+ return 0;
+}
+
int
virPCIDeviceReset(virPCIDevice *dev,
virPCIDeviceList *activeDevs,
@@ -1146,9 +1221,17 @@ virPCIDeviceReset(virPCIDevice *dev,
if (dev->has_pm_reset)
ret = virPCIDeviceTryPowerManagementReset(dev, fd);
- /* Bus reset is not an option with the root bus */
- if (ret < 0 && dev->address.bus != 0)
- ret = virPCIDeviceTrySecondaryBusReset(dev, fd, inactiveDevs);
+ /* Bus reset is not an option with the root bus. On multi-root
+ * systems like Intel Arrow Lake, root buses can be non-zero (e.g., 0x80),
+ * so we use sysfs topology detection instead of checking bus == 0.
+ */
+ if (ret < 0) {
+ int onRootBus = virPCIDeviceIsOnRootBus(dev);
+ if (onRootBus < 0)
+ goto cleanup;
+ if (!onRootBus)
+ ret = virPCIDeviceTrySecondaryBusReset(dev, fd, inactiveDevs);
+ }
if (ret < 0) {
virErrorPtr err = virGetLastError();
@@ -2531,15 +2614,24 @@ static int
virPCIDeviceIsBehindSwitchLackingACS(virPCIDevice *dev)
{
g_autoptr(virPCIDevice) parent = NULL;
+ int onRootBus;
if (virPCIDeviceGetParent(dev, &parent) < 0)
return -1;
if (!parent) {
- /* if we have no parent, and this is the root bus, ACS doesn't come
- * into play since devices on the root bus can't P2P without going
- * through the root IOMMU.
+ /* If we have no parent bridge, check if the device is directly
+ * attached to a root bus. Systems like Intel Arrow Lake can have
+ * multiple root buses (e.g., 0x00 and 0x80), so we can't just
+ * check for bus == 0. Instead, use sysfs topology to detect
+ * root bus attachment.
+ *
+ * ACS doesn't come into play for devices on root buses since
+ * they can't P2P without going through the root IOMMU.
*/
- if (dev->address.bus == 0) {
+ onRootBus = virPCIDeviceIsOnRootBus(dev);
+ if (onRootBus < 0)
+ return -1;
+ if (onRootBus) {
return 0;
} else {
virReportError(VIR_ERR_INTERNAL_ERROR,
--
2.47.3
