vfio/pci: detect the support of dynamic MSI-X allocation

Kernel provides the guidance of dynamic MSI-X allocation support of
passthrough device, by clearing the VFIO_IRQ_INFO_NORESIZE flag to
guide user space.

Fetch the flags from host to determine if dynamic MSI-X allocation is
supported.

Originally-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Jing Liu <jing2.liu@intel.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Cédric Le Goater <clg@redhat.com>

hw/vfio/pci.c

@@ -1493,7 +1493,9 @@ static void vfio_msix_early_setup(VFIOPCIDevice *vdev, Error **errp)
     uint8_t pos;
     uint16_t ctrl;
     uint32_t table, pba;
-    int fd = vdev->vbasedev.fd;
+    int ret, fd = vdev->vbasedev.fd;
+    struct vfio_irq_info irq_info = { .argsz = sizeof(irq_info),
+                                      .index = VFIO_PCI_MSIX_IRQ_INDEX };
     VFIOMSIXInfo *msix;
 
     pos = pci_find_capability(&vdev->pdev, PCI_CAP_ID_MSIX);
@@ -1530,6 +1532,15 @@ static void vfio_msix_early_setup(VFIOPCIDevice *vdev, Error **errp)
     msix->pba_offset = pba & ~PCI_MSIX_FLAGS_BIRMASK;
     msix->entries = (ctrl & PCI_MSIX_FLAGS_QSIZE) + 1;
 
+    ret = ioctl(vdev->vbasedev.fd, VFIO_DEVICE_GET_IRQ_INFO, &irq_info);
+    if (ret < 0) {
+        error_setg_errno(errp, -ret, "failed to get MSI-X irq info");
+        g_free(msix);
+        return;
+    }
+
+    msix->noresize = !!(irq_info.flags & VFIO_IRQ_INFO_NORESIZE);
+
     /*
      * Test the size of the pba_offset variable and catch if it extends outside
      * of the specified BAR. If it is the case, we need to apply a hardware
@@ -1562,7 +1573,8 @@ static void vfio_msix_early_setup(VFIOPCIDevice *vdev, Error **errp)
     }
 
     trace_vfio_msix_early_setup(vdev->vbasedev.name, pos, msix->table_bar,
-                                msix->table_offset, msix->entries);
+                                msix->table_offset, msix->entries,
+                                msix->noresize);
     vdev->msix = msix;
 
     vfio_pci_fixup_msix_region(vdev);

hw/vfio/pci.h

@@ -113,6 +113,7 @@ typedef struct VFIOMSIXInfo {
     uint32_t table_offset;
     uint32_t pba_offset;
     unsigned long *pending;
+    bool noresize;
 } VFIOMSIXInfo;
 
 #define TYPE_VFIO_PCI "vfio-pci"

hw/vfio/trace-events

@@ -27,7 +27,7 @@ vfio_vga_read(uint64_t addr, int size, uint64_t data) " (0x%"PRIx64", %d) = 0x%"
 vfio_pci_read_config(const char *name, int addr, int len, int val) " (%s, @0x%x, len=0x%x) 0x%x"
 vfio_pci_write_config(const char *name, int addr, int val, int len) " (%s, @0x%x, 0x%x, len=0x%x)"
 vfio_msi_setup(const char *name, int pos) "%s PCI MSI CAP @0x%x"
-vfio_msix_early_setup(const char *name, int pos, int table_bar, int offset, int entries) "%s PCI MSI-X CAP @0x%x, BAR %d, offset 0x%x, entries %d"
+vfio_msix_early_setup(const char *name, int pos, int table_bar, int offset, int entries, bool noresize) "%s PCI MSI-X CAP @0x%x, BAR %d, offset 0x%x, entries %d, noresize %d"
 vfio_check_pcie_flr(const char *name) "%s Supports FLR via PCIe cap"
 vfio_check_pm_reset(const char *name) "%s Supports PM reset"
 vfio_check_af_flr(const char *name) "%s Supports FLR via AF cap"