VT-d: fix VF of RC integrated PF matched to wrong VT-d unit

The problem is for a VF of RC integrated PF (e.g. PF's BDF is 00:02.0),
we would wrongly use 00:00.0 to search VT-d unit.

If a PF is an extended function, the BDF of a traditional function within the
same device should be used to search VT-d unit. Otherwise, the real BDF of PF
should be used. According PCI-e spec, an extended function is a function
within an ARI device and Function Number is greater than 7. The original code
tried to tell apart them through checking PCI_SLOT(), missing counterpart of
pci_ari_enabled() (this function exists in linux kernel) compared to linux
kernel. Without checking whether ARI is enabled, it incurs a RC integrated PF
with PCI_SLOT() >0 is wrongly classified to an extended function. Note that a
RC integrated function isn't within an ARI device and thus cannot be extended
function and in this case the real BDF should be used.

Considering 'is_extfn' field of struct pci_dev has been passed down from
Domain0 to indicate whether the function is an extended function, this patch
just looks up the 'is_extfn' field of PF's struct pci_dev and set 'devfn' to 0
when 'is_extfn' is true.

Reported-by: Crawford, Eric R <Eric.R.Crawford@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>

xen/drivers/passthrough/vtd/dmar.c

@@ -218,8 +218,17 @@ struct acpi_drhd_unit *acpi_find_matched_drhd_unit(const struct pci_dev *pdev)
     }
     else if ( pdev->info.is_virtfn )
     {
+        const struct pci_dev *physfn;
+
         bus = pdev->info.physfn.bus;
-        devfn = PCI_SLOT(pdev->info.physfn.devfn) ? 0 : pdev->info.physfn.devfn;
+        /*
+         * Use 0 as 'devfn' to search VT-d unit when the physical function
+         * is an Extended Function.
+         */
+        pcidevs_lock();
+        physfn = pci_get_pdev(pdev->seg, bus, pdev->info.physfn.devfn);
+        devfn = (physfn && physfn->info.is_extfn) ? 0 : pdev->info.physfn.devfn;
+        pcidevs_unlock();
     }
     else
     {