tools/libxl: Skip invalid IRQs

A PCI device's irq field is an 8-bit number.  A value of 0xff indicates
that the device IRQ is not connected.  Additionally, the Linux ACPI code
can convert these 0xff values to IRQ_NOTCONNECTED(0x80000000) because
"0x80000000 is guaranteed to be outside the available range of
interrupts and easy to distinguish from other possible incorrect
values."  When the hypercall to assign that IRQ fails, device
passthrough as a whole fails.

Add checking for a valid IRQ and skip the IRQ handling for PCI devices
outside that range.  This allows for passthrough of devices without
legacy IRQs.

Signed-off-by: Jason Andryuk <jason.andryuk@amd.com>
Reviewed-by: Anthony PERARD <anthony.perard@vates.tech>

tools/libs/light/libxl_pci.c

@@ -26,6 +26,9 @@
 #define PCI_BDF_XSPATH         "%04x-%02x-%02x-%01x"
 #define PCI_PT_QDEV_ID         "pci-pt-%02x_%02x.%01x"
 
+/* PCI Interrupt Line is an 8-bit value, 0xff means disconnected. */
+#define PCI_IRQ_LINE_LIMIT     0xff
+
 static unsigned int pci_encode_bdf(libxl_device_pci *pci)
 {
     unsigned int value;
@@ -1495,7 +1498,7 @@ static void pci_add_dm_done(libxl__egc *egc,
             LOGED(ERROR, domainid, "Couldn't open %s", sysfs_path);
             goto out_no_irq;
         }
-        if ((fscanf(f, "%u", &irq) == 1) && irq) {
+        if (fscanf(f, "%u", &irq) == 1 && irq > 0 && irq < PCI_IRQ_LINE_LIMIT) {
             r = xc_physdev_map_pirq(ctx->xch, domid, irq, &irq);
             if (r < 0) {
                 LOGED(ERROR, domainid, "xc_physdev_map_pirq irq=%d (error=%d)",
@@ -2257,7 +2260,7 @@ skip_bar:
             goto skip_legacy_irq;
         }
 
-        if ((fscanf(f, "%u", &irq) == 1) && irq) {
+        if (fscanf(f, "%u", &irq) == 1 && irq > 0 && irq < PCI_IRQ_LINE_LIMIT) {
             rc = xc_physdev_unmap_pirq(ctx->xch, domid, irq);
             if (rc < 0) {
                 /*