Re: [PATCH] vfio/igd: Check host PCI address when probing

[Cédric Le Goater]

+ Corvin

On 4/9/25 19:18, Alex Williamson wrote:
On Wed, 26 Mar 2025 01:22:39 +0800
Tomita Moeko <tomitamo...@gmail.com> wrote:
So far, all Intel VGA adapters, including discrete GPUs like A770 and
B580, were treated as IGD devices. While this had no functional impact,
a error about "unsupported IGD device" will be printed when passthrough
Intel discrete GPUs.

Since IGD devices must be at "0000:00:02.0", let's check the host PCI
address when probing.

Signed-off-by: Tomita Moeko <tomitamo...@gmail.com>
---
  hw/vfio/igd.c | 23 +++++++++--------------
  1 file changed, 9 insertions(+), 14 deletions(-)

diff --git a/hw/vfio/igd.c b/hw/vfio/igd.c
index 265fffc2aa..ff250017b0 100644
--- a/hw/vfio/igd.c
+++ b/hw/vfio/igd.c
@@ -53,6 +53,13 @@
   * headless setup is desired, the OpRegion gets in the way of that.
   */
  
+static bool vfio_is_igd(VFIOPCIDevice *vdev)
+{
+    return vfio_pci_is(vdev, PCI_VENDOR_ID_INTEL, PCI_ANY_ID) &&
+           vfio_is_vga(vdev) &&
+           vfio_pci_host_match(&vdev->host, "0000:00:02.0");
+}

vfio-pci devices can also be specified via sysfsdev= rather than host=,
so at a minimum I think we'd need to test against vdev->vbasedev.name,
as other callers of vfio_pci_host_match do.  For example building a
local PCIHostDeviceAddress and comparing it to name.  This is also not
foolproof though if we start taking advantage of devices passed by fd.

Could we instead rely PCIe capabilities?  A discrete GPU should
identify as either an endpoint or legacy endpoint and IGD should
identify as a root complex integrated endpoint, or maybe older versions
would lack the PCIe capability altogether.

Maintaining a list of PCI IDs for Intel GPU devices as Corvin was
proposing in [1] is not a viable solution ?

Thanks,

C.

[1] 
https://lore.kernel.org/qemu-devel/20250206121341.118337-1-corvin.koe...@gmail.com/
 
Also I think the comments that were dropped below are still valid and
useful to transfer to this new helper.  I think those are actually
referring to the guest address of 00:02.0 though, which should maybe be
a test as well.  Thanks,

Alex

+
  /*
   * This presumes the device is already known to be an Intel VGA device, so we
   * take liberties in which device ID bits match which generation.  This should
@@ -427,13 +434,7 @@ void vfio_probe_igd_bar0_quirk(VFIOPCIDevice *vdev, int nr)
      VFIOConfigMirrorQuirk *ggc_mirror, *bdsm_mirror;
      int gen;
  
-    /*
-     * This must be an Intel VGA device at address 00:02.0 for us to even
-     * consider enabling legacy mode. Some driver have dependencies on the PCI
-     * bus address.
-     */
-    if (!vfio_pci_is(vdev, PCI_VENDOR_ID_INTEL, PCI_ANY_ID) ||
-        !vfio_is_vga(vdev) || nr != 0) {
+    if (nr != 0 || !vfio_is_igd(vdev)) {
          return;
      }
  
@@ -490,13 +491,7 @@ static bool vfio_pci_igd_config_quirk(VFIOPCIDevice *vdev, Error **errp)
      bool legacy_mode_enabled = false;
      Error *err = NULL;
  
-    /*
-     * This must be an Intel VGA device at address 00:02.0 for us to even
-     * consider enabling legacy mode.  The vBIOS has dependencies on the
-     * PCI bus address.
-     */
-    if (!vfio_pci_is(vdev, PCI_VENDOR_ID_INTEL, PCI_ANY_ID) ||
-        !vfio_is_vga(vdev)) {
+    if (!vfio_is_igd(vdev)) {
          return true;
      }