xen/arm: enable dom0 to use PCI devices with pci-passthrough=no

Enable the use of IOMMU + PCI in dom0 without having to specify
"pci-passthrough=yes". Due to possible platform specific dependencies
of the PCI host, we rely on dom0 to initialize it and perform
a PCI PHYSDEVOP calls to add each device to SMMU.

Because pci_passthrough is not always enabled on all architectures, add
a new function arch_pci_device_physdevop that checks if we need to enable
a subset of the PCI subsystem related to managing IOMMU configuration
for PCI devices.

Enable pci_init() for initializing Xen's internal PCI subsystem, and
allow PCI PHYSDEV ops when pci-passthrough is disabled.

Signed-off-by: Stewart Hildebrand <stewart.hildebrand@amd.com>
Signed-off-by: Mykyta Poturai <mykyta_poturai@epam.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/arch/arm/include/asm/pci.h

@@ -151,6 +151,8 @@ void pci_generic_init_bus_range_child(struct dt_device_node *dev,
                                       struct pci_host_bridge *bridge,
                                       struct pci_config_window *cfg);
 
+bool arch_pci_device_physdevop(void);
+
 #else   /*!CONFIG_HAS_PCI*/
 
 struct pci_dev;

xen/arch/arm/pci/pci.c

@@ -16,6 +16,7 @@
 #include <xen/device_tree.h>
 #include <xen/errno.h>
 #include <xen/init.h>
+#include <xen/iommu.h>
 #include <xen/param.h>
 #include <xen/pci.h>
 
@@ -75,6 +76,17 @@ static int __init acpi_pci_init(void)
 }
 #endif
 
+/*
+ * Platform-specific PCI host dependencies require dom0 to handle
+ * initialization and issue PHYSDEVOP_pci_device_add/remove calls for SMMU
+ * device registration. This check is used to enable the minimal PCI
+ * subsystem required for dom0 operation when PCI passthrough is disabled.
+ */
+bool arch_pci_device_physdevop(void)
+{
+    return iommu_enabled;
+}
+
 /* By default pci passthrough is disabled. */
 bool __read_mostly pci_passthrough_enabled;
 boolean_param("pci-passthrough", pci_passthrough_enabled);
@@ -85,7 +97,7 @@ static int __init pci_init(void)
      * Enable PCI passthrough when has been enabled explicitly
      * (pci-passthrough=on).
      */
-    if ( !pci_passthrough_enabled )
+    if ( !is_pci_passthrough_enabled() && !arch_pci_device_physdevop() )
         return 0;
 
     if ( pci_add_segment(0) )

xen/arch/x86/include/asm/pci.h

@@ -57,6 +57,16 @@ static always_inline bool is_pci_passthrough_enabled(void)
     return true;
 }
 
+/*
+ * Since PCI passthrough is always enabled on x86, physdevop handling doesn't
+ * need special arch-specific behavior. Current call sites work with either
+ * return value, but true is more consistent with passthrough being enabled.
+ */
+static inline bool arch_pci_device_physdevop(void)
+{
+    return true;
+}
+
 void arch_pci_init_pdev(struct pci_dev *pdev);
 
 bool pci_check_bar(const struct pci_dev *pdev, mfn_t start, mfn_t end);

xen/drivers/pci/physdev.c

@@ -19,7 +19,7 @@ ret_t pci_physdev_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
         struct pci_dev_info pdev_info;
         nodeid_t node = NUMA_NO_NODE;
 
-        if ( !is_pci_passthrough_enabled() )
+        if ( !is_pci_passthrough_enabled() && !arch_pci_device_physdevop() )
             return -EOPNOTSUPP;
 
         ret = -EFAULT;
@@ -57,7 +57,7 @@ ret_t pci_physdev_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
     case PHYSDEVOP_pci_device_remove: {
         struct physdev_pci_device dev;
 
-        if ( !is_pci_passthrough_enabled() )
+        if ( !is_pci_passthrough_enabled() && !arch_pci_device_physdevop() )
             return -EOPNOTSUPP;
 
         ret = -EFAULT;
@@ -74,7 +74,7 @@ ret_t pci_physdev_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
         struct pci_dev *pdev;
         pci_sbdf_t sbdf;
 
-        if ( !is_pci_passthrough_enabled() )
+        if ( !is_pci_passthrough_enabled() && !arch_pci_device_physdevop() )
             return -EOPNOTSUPP;
 
         ret = -EFAULT;

xen/include/xen/pci.h

@@ -79,6 +79,11 @@ static inline bool is_pci_passthrough_enabled(void)
     return false;
 }
 
+static inline bool arch_pci_device_physdevop(void)
+{
+    return false;
+}
+
 #endif
 
 struct pci_dev_info {