[PATCH v2 2/2] xen: fix stubdom PCI addr

["Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>]

From: Frédéric Pierret (fepitre) <frederic.pierret@qubes-os.org>

When running in a stubdomain, the config space access via sysfs needs to
use BDF as seen inside stubdomain (connected via xen-pcifront), which is
different from the real BDF. For other purposes (hypercall parameters
etc), the real BDF needs to be used.
Get the in-stubdomain BDF by looking up relevant PV PCI xenstore
entries.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
---
Changes in v2:
- use xs_node_scanf
- use %d instead of %u to read values written as %d
- add a comment from another iteration of this patch by Jason Andryuk
---
 hw/xen/xen-host-pci-device.c | 69 +++++++++++++++++++++++++++++++++++-
 hw/xen/xen-host-pci-device.h |  6 ++++
 2 files changed, 74 insertions(+), 1 deletion(-)

diff --git a/hw/xen/xen-host-pci-device.c b/hw/xen/xen-host-pci-device.c
index 8c6e9a1716..8ea2a5a4af 100644
--- a/hw/xen/xen-host-pci-device.c
+++ b/hw/xen/xen-host-pci-device.c
@@ -9,6 +9,8 @@
 #include "qemu/osdep.h"
 #include "qapi/error.h"
 #include "qemu/cutils.h"
+#include "hw/xen/xen-legacy-backend.h"
+#include "hw/xen/xen-bus-helper.h"
 #include "xen-host-pci-device.h"
 
 #define XEN_HOST_PCI_MAX_EXT_CAP \
@@ -33,13 +35,67 @@
 #define IORESOURCE_PREFETCH     0x00001000      /* No side effects */
 #define IORESOURCE_MEM_64       0x00100000
 
+/*
+ * Non-passthrough (dom0) accesses are local PCI devices and use the given BDF
+ * Passthough (stubdom) accesses are through PV frontend PCI device.  Those
+ * either have a BDF identical to the backend's BDF (xen-backend.passthrough=1)
+ * or a local virtual BDF (xen-backend.passthrough=0)
+ *
+ * We are always given the backend's BDF and need to lookup the appropriate
+ * local BDF for sysfs access.
+ */
+static void xen_host_pci_fill_local_addr(XenHostPCIDevice *d, Error **errp)
+{
+    unsigned int num_devs, len, i;
+    unsigned int domain, bus, dev, func;
+    char *be_path = NULL;
+    char path[80];
+
+    be_path = qemu_xen_xs_read(xenstore, 0, "device/pci/0/backend", &len);
+    if (!be_path)
+        goto out;
+
+    if (xs_node_scanf(xenstore, 0, be_path, "num_devs", NULL, "%d", &num_devs) != 1) {
+        error_setg(errp, "Failed to read or parse %s/num_devs\n", be_path);
+        goto out;
+    }
+
+    for (i = 0; i < num_devs; i++) {
+        snprintf(path, sizeof(path), "dev-%d", i);
+        if (xs_node_scanf(xenstore, 0, be_path, path, NULL,
+                          "%x:%x:%x.%x", &domain, &bus, &dev, &func) != 4) {
+            error_setg(errp, "Failed to read or parse %s/%s\n", be_path, path);
+            goto out;
+        }
+        if (domain != d->domain ||
+                bus != d->bus ||
+                dev != d->dev ||
+                func!= d->func)
+            continue;
+        snprintf(path, sizeof(path), "vdev-%d", i);
+        if (xs_node_scanf(xenstore, 0, be_path, path, NULL,
+                          "%x:%x:%x.%x", &domain, &bus, &dev, &func) != 4) {
+            error_setg(errp, "Failed to read or parse %s/%s\n", be_path, path);
+            goto out;
+        }
+        d->local_domain = domain;
+        d->local_bus = bus;
+        d->local_dev = dev;
+        d->local_func = func;
+        goto out;
+    }
+
+out:
+    free(be_path);
+}
+
 static void xen_host_pci_sysfs_path(const XenHostPCIDevice *d,
                                     const char *name, char *buf, ssize_t size)
 {
     int rc;
 
     rc = snprintf(buf, size, "/sys/bus/pci/devices/%04x:%02x:%02x.%d/%s",
-                  d->domain, d->bus, d->dev, d->func, name);
+                  d->local_domain, d->local_bus, d->local_dev, d->local_func, name);
     assert(rc >= 0 && rc < size);
 }
 
@@ -342,6 +398,17 @@ void xen_host_pci_device_get(XenHostPCIDevice *d, uint16_t domain,
     d->dev = dev;
     d->func = func;
 
+    if (xen_is_stubdomain) {
+        xen_host_pci_fill_local_addr(d, errp);
+        if (*errp)
+            goto error;
+    } else {
+        d->local_domain = d->domain;
+        d->local_bus = d->bus;
+        d->local_dev = d->dev;
+        d->local_func = d->func;
+    }
+
     xen_host_pci_config_open(d, errp);
     if (*errp) {
         goto error;
diff --git a/hw/xen/xen-host-pci-device.h b/hw/xen/xen-host-pci-device.h
index 4d8d34ecb0..270dcb27f7 100644
--- a/hw/xen/xen-host-pci-device.h
+++ b/hw/xen/xen-host-pci-device.h
@@ -23,6 +23,12 @@ typedef struct XenHostPCIDevice {
     uint8_t dev;
     uint8_t func;
 
+    /* different from the above in case of stubdomain */
+    uint16_t local_domain;
+    uint8_t local_bus;
+    uint8_t local_dev;
+    uint8_t local_func;
+
     uint16_t vendor_id;
     uint16_t device_id;
     uint32_t class_code;
-- 
2.43.0