[PATCH] IOMMU/VT-d: Fix iommu=no-igfx if the IOMMU scope contains phantom device

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

If the scope for IGD's IOMMU contains additional device that doesn't
actually exist, iommu=no-igfx would not disable that IOMMU. In this
particular case (Thinkpad x230) it included
00:02.1, but there is no such device on this platform.
Consider only existing devices for "gfx only" check.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
---
I have looked at existence check acpi_parse_one_drhd(), but re-using
that one wouldn't work for two reasons:
 - gfx_only logic is very much tied to acpi_parse_dev_scope()
 - pci_device_detect() in acpi_parse_one_drhd() is skipped in case of
   (implicit or explicit) iommu=force
---
 xen/drivers/passthrough/vtd/dmar.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/xen/drivers/passthrough/vtd/dmar.c 
b/xen/drivers/passthrough/vtd/dmar.c
index 78c8bad1515a..3b5e152901b9 100644
--- a/xen/drivers/passthrough/vtd/dmar.c
+++ b/xen/drivers/passthrough/vtd/dmar.c
@@ -396,6 +396,7 @@ static int __init acpi_parse_dev_scope(
                     igd_drhd_address = drhd->address;
 
                 if ( gfx_only &&
+                     pci_device_detect(seg, bus, path->dev, path->fn) &&
                      pci_conf_read8(PCI_SBDF(seg, bus, path->dev, path->fn),
                                     PCI_CLASS_DEVICE + 1) != 0x03
                                     /* PCI_BASE_CLASS_DISPLAY */ )
-- 
2.39.2