xen-pciback: allow compiling on other archs than x86

Xen-pciback driver was designed to be built for x86 only. But it
can also be used by other architectures, e.g. Arm.

Currently PCI backend implements multiple functionalities at a time,
such as:
1. It is used as a database for assignable PCI devices, e.g. xl
pci-assignable-{add|remove|list} manipulates that list. So, whenever
the toolstack needs to know which PCI devices can be passed through
it reads that from the relevant sysfs entries of the pciback.
2. It is used to hold the unbound PCI devices list, e.g. when passing
through a PCI device it needs to be unbound from the relevant device
driver and bound to pciback (strictly speaking it is not required
that the device is bound to pciback, but pciback is again used as a
database of the passed through PCI devices, so we can re-bind the
devices back to their original drivers when guest domain shuts down)
3. Device reset for the devices being passed through
4. Para-virtualised use-cases support

The para-virtualised part of the driver is not always needed as some
architectures, e.g. Arm or x86 PVH Dom0, are not using backend-frontend
model for PCI device passthrough.

For such use-cases make the very first step in splitting the
xen-pciback driver into two parts: Xen PCI stub and PCI PV backend
drivers.

For that add new configuration options CONFIG_XEN_PCI_STUB and
CONFIG_XEN_PCIDEV_STUB, so the driver can be limited in its
functionality, e.g. no support for para-virtualised scenario.
x86 platform will continue using CONFIG_XEN_PCIDEV_BACKEND for the
fully featured backend driver.

Signed-off-by: Oleksandr Andrushchenko <[e-mail]>
Signed-off-by: Anastasiia Lukianenko <[e-mail]>
Reviewed-by: Stefano Stabellini <[e-mail]>
Reviewed-by: Juergen Gross <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Boris Ostrovsky <[e-mail]>

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

···
 	return -1;
 }
 #endif
-#ifdef CONFIG_XEN_DOM0
-int xen_find_device_domain_owner(struct pci_dev *dev);
-int xen_register_device_domain_owner(struct pci_dev *dev, uint16_t domain);
-int xen_unregister_device_domain_owner(struct pci_dev *dev);
-#else
-static inline int xen_find_device_domain_owner(struct pci_dev *dev)
-{
-	return -1;
-}
-static inline int xen_register_device_domain_owner(struct pci_dev *dev,
-						   uint16_t domain)
-{
-	return -1;
-}
-static inline int xen_unregister_device_domain_owner(struct pci_dev *dev)
-{
-	return -1;
-}
-#endif
 
 #if defined(CONFIG_PCI_MSI)
 #if defined(CONFIG_PCI_XEN)

arch/x86/pci/xen.c

···
 
 #include <xen/features.h>
 #include <xen/events.h>
+#include <xen/pci.h>
 #include <asm/xen/pci.h>
 #include <asm/xen/cpuid.h>
 #include <asm/apic.h>
···
 }
 #endif
 
-#ifdef CONFIG_XEN_DOM0
-
-struct xen_device_domain_owner {
-	domid_t domain;
-	struct pci_dev *dev;
-	struct list_head list;
-};
-
-static DEFINE_SPINLOCK(dev_domain_list_spinlock);
-static struct list_head dev_domain_list = LIST_HEAD_INIT(dev_domain_list);
-
-static struct xen_device_domain_owner *find_device(struct pci_dev *dev)
-{
-	struct xen_device_domain_owner *owner;
-
-	list_for_each_entry(owner, &dev_domain_list, list) {
-		if (owner->dev == dev)
-			return owner;
-	}
-	return NULL;
-}
-
-int xen_find_device_domain_owner(struct pci_dev *dev)
-{
-	struct xen_device_domain_owner *owner;
-	int domain = -ENODEV;
-
-	spin_lock(&dev_domain_list_spinlock);
-	owner = find_device(dev);
-	if (owner)
-		domain = owner->domain;
-	spin_unlock(&dev_domain_list_spinlock);
-	return domain;
-}
-EXPORT_SYMBOL_GPL(xen_find_device_domain_owner);
-
-int xen_register_device_domain_owner(struct pci_dev *dev, uint16_t domain)
-{
-	struct xen_device_domain_owner *owner;
-
-	owner = kzalloc(sizeof(struct xen_device_domain_owner), GFP_KERNEL);
-	if (!owner)
-		return -ENODEV;
-
-	spin_lock(&dev_domain_list_spinlock);
-	if (find_device(dev)) {
-		spin_unlock(&dev_domain_list_spinlock);
-		kfree(owner);
-		return -EEXIST;
-	}
-	owner->domain = domain;
-	owner->dev = dev;
-	list_add_tail(&owner->list, &dev_domain_list);
-	spin_unlock(&dev_domain_list_spinlock);
-	return 0;
-}
-EXPORT_SYMBOL_GPL(xen_register_device_domain_owner);
-
-int xen_unregister_device_domain_owner(struct pci_dev *dev)
-{
-	struct xen_device_domain_owner *owner;
-
-	spin_lock(&dev_domain_list_spinlock);
-	owner = find_device(dev);
-	if (!owner) {
-		spin_unlock(&dev_domain_list_spinlock);
-		return -ENODEV;
-	}
-	list_del(&owner->list);
-	spin_unlock(&dev_domain_list_spinlock);
-	kfree(owner);
-	return 0;
-}
-EXPORT_SYMBOL_GPL(xen_unregister_device_domain_owner);
-#endif /* CONFIG_XEN_DOM0 */

drivers/xen/Kconfig

···
 	select DMA_OPS
 	select SWIOTLB
 
+config XEN_PCI_STUB
+	bool
+
+config XEN_PCIDEV_STUB
+	tristate "Xen PCI-device stub driver"
+	depends on PCI && !X86 && XEN
+	depends on XEN_BACKEND
+	select XEN_PCI_STUB
+	default m
+	help
+	  The PCI device stub driver provides limited version of the PCI
+	  device backend driver without para-virtualized support for guests.
+	  If you select this to be a module, you will need to make sure no
+	  other driver has bound to the device(s) you want to make visible to
+	  other guests.
+
+	  The "hide" parameter (only applicable if backend driver is compiled
+	  into the kernel) allows you to bind the PCI devices to this module
+	  from the default device drivers. The argument is the list of PCI BDFs:
+	  xen-pciback.hide=(03:00.0)(04:00.0)
+
+	  If in doubt, say m.
+
 config XEN_PCIDEV_BACKEND
 	tristate "Xen PCI-device backend driver"
 	depends on PCI && X86 && XEN
 	depends on XEN_BACKEND
+	select XEN_PCI_STUB
 	default m
 	help
 	  The PCI device backend driver allows the kernel to export arbitrary

drivers/xen/Makefile

···
 obj-$(CONFIG_XEN_PVHVM_GUEST)		+= platform-pci.o
 obj-$(CONFIG_SWIOTLB_XEN)		+= swiotlb-xen.o
 obj-$(CONFIG_XEN_MCE_LOG)		+= mcelog.o
-obj-$(CONFIG_XEN_PCIDEV_BACKEND)	+= xen-pciback/
+obj-$(CONFIG_XEN_PCI_STUB)	        += xen-pciback/
 obj-$(CONFIG_XEN_PRIVCMD)		+= xen-privcmd.o
 obj-$(CONFIG_XEN_ACPI_PROCESSOR)	+= xen-acpi-processor.o
 obj-$(CONFIG_XEN_EFI)			+= efi.o

drivers/xen/pci.c

···
 #include <linux/pci.h>
 #include <linux/acpi.h>
 #include <linux/pci-acpi.h>
+#include <xen/pci.h>
 #include <xen/xen.h>
 #include <xen/interface/physdev.h>
 #include <xen/interface/xen.h>
···
 	}
 	return 0;
 }
+#endif
+
+#ifdef CONFIG_XEN_DOM0
+struct xen_device_domain_owner {
+	domid_t domain;
+	struct pci_dev *dev;
+	struct list_head list;
+};
+
+static DEFINE_SPINLOCK(dev_domain_list_spinlock);
+static struct list_head dev_domain_list = LIST_HEAD_INIT(dev_domain_list);
+
+static struct xen_device_domain_owner *find_device(struct pci_dev *dev)
+{
+	struct xen_device_domain_owner *owner;
+
+	list_for_each_entry(owner, &dev_domain_list, list) {
+		if (owner->dev == dev)
+			return owner;
+	}
+	return NULL;
+}
+
+int xen_find_device_domain_owner(struct pci_dev *dev)
+{
+	struct xen_device_domain_owner *owner;
+	int domain = -ENODEV;
+
+	spin_lock(&dev_domain_list_spinlock);
+	owner = find_device(dev);
+	if (owner)
+		domain = owner->domain;
+	spin_unlock(&dev_domain_list_spinlock);
+	return domain;
+}
+EXPORT_SYMBOL_GPL(xen_find_device_domain_owner);
+
+int xen_register_device_domain_owner(struct pci_dev *dev, uint16_t domain)
+{
+	struct xen_device_domain_owner *owner;
+
+	owner = kzalloc(sizeof(struct xen_device_domain_owner), GFP_KERNEL);
+	if (!owner)
+		return -ENODEV;
+
+	spin_lock(&dev_domain_list_spinlock);
+	if (find_device(dev)) {
+		spin_unlock(&dev_domain_list_spinlock);
+		kfree(owner);
+		return -EEXIST;
+	}
+	owner->domain = domain;
+	owner->dev = dev;
+	list_add_tail(&owner->list, &dev_domain_list);
+	spin_unlock(&dev_domain_list_spinlock);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(xen_register_device_domain_owner);
+
+int xen_unregister_device_domain_owner(struct pci_dev *dev)
+{
+	struct xen_device_domain_owner *owner;
+
+	spin_lock(&dev_domain_list_spinlock);
+	owner = find_device(dev);
+	if (!owner) {
+		spin_unlock(&dev_domain_list_spinlock);
+		return -ENODEV;
+	}
+	list_del(&owner->list);
+	spin_unlock(&dev_domain_list_spinlock);
+	kfree(owner);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(xen_unregister_device_domain_owner);
 #endif

drivers/xen/xen-pciback/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
+
+# N.B. The below cannot be expressed with a single line using
+# CONFIG_XEN_PCI_STUB as it always remains in "y" state,
+# thus preventing the driver to be built as a module.
+# Please note, that CONFIG_XEN_PCIDEV_BACKEND and
+# CONFIG_XEN_PCIDEV_STUB are mutually exclusive.
 obj-$(CONFIG_XEN_PCIDEV_BACKEND) += xen-pciback.o
+obj-$(CONFIG_XEN_PCIDEV_STUB) += xen-pciback.o
 
 xen-pciback-y := pci_stub.o pciback_ops.o xenbus.o
 xen-pciback-y += conf_space.o conf_space_header.o \

drivers/xen/xen-pciback/conf_space_header.c

···
 	else {
 		pos = (offset - PCI_BASE_ADDRESS_0) / 4;
 		if (pos && (res[pos - 1].flags & IORESOURCE_MEM_64)) {
-			bar->val = res[pos - 1].start >> 32;
-			bar->len_val = -resource_size(&res[pos - 1]) >> 32;
+			/*
+			 * Use ">> 16 >> 16" instead of direct ">> 32" shift
+			 * to avoid warnings on 32-bit architectures.
+			 */
+			bar->val = res[pos - 1].start >> 16 >> 16;
+			bar->len_val = -resource_size(&res[pos - 1]) >> 16 >> 16;
 			return bar;
 		}
 	}

drivers/xen/xen-pciback/pci_stub.c

···
 #include <linux/sched.h>
 #include <linux/atomic.h>
 #include <xen/events.h>
-#include <asm/xen/pci.h>
+#include <xen/pci.h>
+#include <xen/xen.h>
 #include <asm/xen/hypervisor.h>
 #include <xen/interface/physdev.h>
 #include "pciback.h"

drivers/xen/xen-pciback/pciback.h

···
 				    struct pci_dev *dev);
 void pcistub_put_pci_dev(struct pci_dev *dev);
 
+static inline bool xen_pcibk_pv_support(void)
+{
+	return IS_ENABLED(CONFIG_XEN_PCIDEV_BACKEND);
+}
+
 /* Ensure a device is turned off or reset */
 void xen_pcibk_reset_device(struct pci_dev *pdev);
 

drivers/xen/xen-pciback/xenbus.c

···
 #include <linux/workqueue.h>
 #include <xen/xenbus.h>
 #include <xen/events.h>
-#include <asm/xen/pci.h>
+#include <xen/pci.h>
 #include "pciback.h"
 
 #define INVALID_EVTCHN_IRQ  (-1)
···
 
 int __init xen_pcibk_xenbus_register(void)
 {
+	if (!xen_pcibk_pv_support())
+		return 0;
+
 	xen_pcibk_backend = &xen_pcibk_vpci_backend;
 	if (passthrough)
 		xen_pcibk_backend = &xen_pcibk_passthrough_backend;
···
 
 void __exit xen_pcibk_xenbus_unregister(void)
 {
-	xenbus_unregister_driver(&xen_pcibk_driver);
+	if (xen_pcibk_pv_support())
+		xenbus_unregister_driver(&xen_pcibk_driver);
 }

include/xen/pci.h

···
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __XEN_PCI_H__
+#define __XEN_PCI_H__
+
+#if defined(CONFIG_XEN_DOM0)
+int xen_find_device_domain_owner(struct pci_dev *dev);
+int xen_register_device_domain_owner(struct pci_dev *dev, uint16_t domain);
+int xen_unregister_device_domain_owner(struct pci_dev *dev);
+#else
+static inline int xen_find_device_domain_owner(struct pci_dev *dev)
+{
+	return -1;
+}
+
+static inline int xen_register_device_domain_owner(struct pci_dev *dev,
+						   uint16_t domain)
+{
+	return -1;
+}
+
+static inline int xen_unregister_device_domain_owner(struct pci_dev *dev)
+{
+	return -1;
+}
+#endif
+
+#endif