[PATCH v4 10/11] vpci: add initial support for virtual PCI bus topology

[Oleksandr Andrushchenko <andr2000@gmail.com>]

From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>

Assign SBDF to the PCI devices being passed through with bus 0.
The resulting topology is where PCIe devices reside on the bus 0 of the
root complex itself (embedded endpoints).
This implementation is limited to 32 devices which are allowed on
a single PCI bus.

Please note, that at the moment only function 0 of a multifunction
device can be passed through.

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
---
Since v3:
 - make use of VPCI_INIT
 - moved all new code to vpci.c which belongs to it
 - changed open-coded 31 to PCI_SLOT(~0)
 - revisited locking: add dedicated vdev list's lock
 - added comments and code to reject multifunction devices with
   functions other than 0
 - updated comment about vpci_dev_next and made it unsigned int
 - implement roll back in case of error while assigning/deassigning devices
 - s/dom%pd/%pd
Since v2:
 - remove casts that are (a) malformed and (b) unnecessary
 - add new line for better readability
 - remove CONFIG_HAS_VPCI_GUEST_SUPPORT ifdef's as the relevant vPCI
    functions are now completely gated with this config
 - gate common code with CONFIG_HAS_VPCI_GUEST_SUPPORT
New in v2
---
 xen/drivers/vpci/vpci.c | 52 +++++++++++++++++++++++++++++++++++++++++
 xen/include/xen/sched.h |  8 +++++++
 xen/include/xen/vpci.h  |  4 ++++
 3 files changed, 64 insertions(+)

diff --git a/xen/drivers/vpci/vpci.c b/xen/drivers/vpci/vpci.c
index 45733300f00b..6657d236dc1a 100644
--- a/xen/drivers/vpci/vpci.c
+++ b/xen/drivers/vpci/vpci.c
@@ -101,6 +101,9 @@ int vpci_add_handlers(struct pci_dev *pdev)
 
     INIT_LIST_HEAD(&pdev->vpci->handlers);
     spin_lock_init(&pdev->vpci->lock);
+#ifdef CONFIG_HAS_VPCI_GUEST_SUPPORT
+    pdev->vpci->guest_sbdf.sbdf = ~0;
+#endif
 
     header = &pdev->vpci->header;
     for ( i = 0; i < ARRAY_SIZE(header->bars); i++ )
@@ -125,6 +128,54 @@ int vpci_add_handlers(struct pci_dev *pdev)
 }
 
 #ifdef CONFIG_HAS_VPCI_GUEST_SUPPORT
+int vpci_add_virtual_device(struct pci_dev *pdev)
+{
+    struct domain *d = pdev->domain;
+    pci_sbdf_t sbdf;
+    unsigned long new_dev_number;
+
+    /*
+     * Each PCI bus supports 32 devices/slots at max or up to 256 when
+     * there are multi-function ones which are not yet supported.
+     */
+    if ( pdev->info.is_extfn )
+    {
+        gdprintk(XENLOG_ERR, "%pp: only function 0 passthrough supported\n",
+                 &pdev->sbdf);
+        return -EOPNOTSUPP;
+    }
+
+    new_dev_number = find_first_zero_bit(&d->vpci_dev_assigned_map,
+                                         PCI_SLOT(~0) + 1);
+    if ( new_dev_number > PCI_SLOT(~0) )
+        return -ENOSPC;
+
+    set_bit(new_dev_number, &d->vpci_dev_assigned_map);
+
+    /*
+     * Both segment and bus number are 0:
+     *  - we emulate a single host bridge for the guest, e.g. segment 0
+     *  - with bus 0 the virtual devices are seen as embedded
+     *    endpoints behind the root complex
+     *
+     * TODO: add support for multi-function devices.
+     */
+    sbdf.sbdf = 0;
+    sbdf.devfn = PCI_DEVFN(new_dev_number, 0);
+    pdev->vpci->guest_sbdf = sbdf;
+
+    return 0;
+
+}
+REGISTER_VPCI_INIT(vpci_add_virtual_device, VPCI_PRIORITY_MIDDLE);
+
+static void vpci_remove_virtual_device(struct domain *d,
+                                       const struct pci_dev *pdev)
+{
+    clear_bit(pdev->vpci->guest_sbdf.dev, &d->vpci_dev_assigned_map);
+    pdev->vpci->guest_sbdf.sbdf = ~0;
+}
+
 /* Notify vPCI that device is assigned to guest. */
 int vpci_assign_device(struct domain *d, struct pci_dev *pdev)
 {
@@ -150,6 +201,7 @@ int vpci_deassign_device(struct domain *d, struct pci_dev *pdev)
     if ( is_system_domain(d) || !has_vpci(d) )
         return 0;
 
+    vpci_remove_virtual_device(d, pdev);
     vpci_remove_device_handlers(pdev);
 
     return 0;
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index 28146ee404e6..10bff103317c 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -444,6 +444,14 @@ struct domain
 
 #ifdef CONFIG_HAS_PCI
     struct list_head pdev_list;
+#ifdef CONFIG_HAS_VPCI_GUEST_SUPPORT
+    /*
+     * The bitmap which shows which device numbers are already used by the
+     * virtual PCI bus topology and is used to assign a unique SBDF to the
+     * next passed through virtual PCI device.
+     */
+    unsigned long vpci_dev_assigned_map;
+#endif
 #endif
 
 #ifdef CONFIG_HAS_PASSTHROUGH
diff --git a/xen/include/xen/vpci.h b/xen/include/xen/vpci.h
index 143f3166a730..9cc7071bc0af 100644
--- a/xen/include/xen/vpci.h
+++ b/xen/include/xen/vpci.h
@@ -145,6 +145,10 @@ struct vpci {
             struct vpci_arch_msix_entry arch;
         } entries[];
     } *msix;
+#ifdef CONFIG_HAS_VPCI_GUEST_SUPPORT
+    /* Virtual SBDF of the device. */
+    pci_sbdf_t guest_sbdf;
+#endif
 #endif
 };
 
-- 
2.25.1