Tests for ACS in PCIe switches

New pciDeviceIsAssignable() function for checking whether a given PCI
device can be assigned to a guest was added. Currently it only checks
for ACS being enabled on all PCIe switches between root and the PCI
device. In the future, it could be the right place to check whether a
device is unbound or bound to a stub driver.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>

src/libvirt_private.syms

@@ -450,6 +450,7 @@ pciDeviceFileIterate;
 pciDeviceListCount;
 pciDeviceListGet;
 pciDeviceListSteal;
+pciDeviceIsAssignable;
 
 
 # processinfo.h

src/util/pci.c

@@ -140,6 +140,28 @@ struct _pciDeviceList {
 #define PCI_AF_CAP              0x3     /* Advanced features capabilities */
 #define  PCI_AF_CAP_FLR         0x2     /* Function Level Reset */
 
+#define PCI_EXP_FLAGS           0x2
+#define PCI_EXP_FLAGS_TYPE      0x00f0
+#define PCI_EXP_TYPE_DOWNSTREAM 0x6
+
+#define PCI_EXT_CAP_BASE          0x100
+#define PCI_EXT_CAP_LIMIT         0x1000
+#define PCI_EXT_CAP_ID_MASK       0x0000ffff
+#define PCI_EXT_CAP_OFFSET_SHIFT  20
+#define PCI_EXT_CAP_OFFSET_MASK   0x00000ffc
+
+#define PCI_EXT_CAP_ID_ACS      0x000d
+#define PCI_EXT_ACS_CTRL        0x06
+
+#define PCI_EXT_CAP_ACS_SV      0x01
+#define PCI_EXT_CAP_ACS_RR      0x04
+#define PCI_EXT_CAP_ACS_CR      0x08
+#define PCI_EXT_CAP_ACS_UF      0x10
+#define PCI_EXT_CAP_ACS_ENABLED (PCI_EXT_CAP_ACS_SV | \
+                                 PCI_EXT_CAP_ACS_RR | \
+                                 PCI_EXT_CAP_ACS_CR | \
+                                 PCI_EXT_CAP_ACS_UF)
+
 static int
 pciOpenConfig(pciDevice *dev)
 {
@@ -326,6 +348,30 @@ pciFindCapabilityOffset(pciDevice *dev, unsigned capability)
     return 0;
 }
 
+static unsigned int
+pciFindExtendedCapabilityOffset(pciDevice *dev, unsigned capability)
+{
+    int ttl;
+    unsigned int pos;
+    uint32_t header;
+
+    /* minimum 8 bytes per capability */
+    ttl = (PCI_EXT_CAP_LIMIT - PCI_EXT_CAP_BASE) / 8;
+    pos = PCI_EXT_CAP_BASE;
+
+    while (ttl > 0 && pos >= PCI_EXT_CAP_BASE) {
+        header = pciRead32(dev, pos);
+
+        if ((header & PCI_EXT_CAP_ID_MASK) == capability)
+            return pos;
+
+        pos = (header >> PCI_EXT_CAP_OFFSET_SHIFT) & PCI_EXT_CAP_OFFSET_MASK;
+        ttl--;
+    }
+
+    return 0;
+}
+
 static unsigned
 pciDetectFunctionLevelReset(pciDevice *dev)
 {
@@ -1110,3 +1156,108 @@ cleanup:
     VIR_FREE(pcidir);
     return ret;
 }
+
+static int
+pciDeviceDownstreamLacksACS(virConnectPtr conn,
+                            pciDevice *dev)
+{
+    uint16_t flags;
+    uint16_t ctrl;
+    unsigned int pos;
+
+    if (!dev->initted && pciInitDevice(conn, dev) < 0)
+        return -1;
+
+    pos = dev->pcie_cap_pos;
+    if (!pos || !pciRead16(dev, PCI_CLASS_DEVICE) == PCI_CLASS_BRIDGE_PCI)
+        return 0;
+
+    flags = pciRead16(dev, pos + PCI_EXP_FLAGS);
+    if (((flags & PCI_EXP_FLAGS_TYPE) >> 4) != PCI_EXP_TYPE_DOWNSTREAM)
+        return 0;
+
+    pos = pciFindExtendedCapabilityOffset(dev, PCI_EXT_CAP_ID_ACS);
+    if (!pos) {
+        VIR_DEBUG("%s %s: downstream port lacks ACS", dev->id, dev->name);
+        return 1;
+    }
+
+    ctrl = pciRead16(dev, pos + PCI_EXT_ACS_CTRL);
+    if ((ctrl & PCI_EXT_CAP_ACS_ENABLED) != PCI_EXT_CAP_ACS_ENABLED) {
+        VIR_DEBUG("%s %s: downstream port has ACS disabled",
+                  dev->id, dev->name);
+        return 1;
+    }
+
+    return 0;
+}
+
+static int
+pciDeviceIsBehindSwitchLackingACS(virConnectPtr conn,
+                                  pciDevice *dev)
+{
+    pciDevice *parent;
+
+    if (!(parent = pciGetParentDevice(conn, dev))) {
+        pciReportError(conn, VIR_ERR_NO_SUPPORT,
+                       _("Failed to find parent device for %s"),
+                       dev->name);
+        return -1;
+    }
+
+    /* XXX we should rather fail when we can't find device's parent and
+     * stop the loop when we get to root instead of just stopping when no
+     * parent can be found
+     */
+    do {
+        pciDevice *tmp;
+        int acs;
+
+        acs = pciDeviceDownstreamLacksACS(conn, parent);
+
+        if (acs) {
+            pciFreeDevice(conn, parent);
+            if (acs < 0)
+                return -1;
+            else
+                return 1;
+        }
+
+        tmp = parent;
+        parent = pciGetParentDevice(conn, parent);
+        pciFreeDevice(conn, tmp);
+    } while (parent);
+
+    return 0;
+}
+
+int pciDeviceIsAssignable(virConnectPtr conn,
+                          pciDevice *dev,
+                          int strict_acs_check)
+{
+    int ret;
+
+    /* XXX This could be a great place to actually check that a non-managed
+     * device isn't in use, e.g. by checking that device is either un-bound
+     * or bound to a stub driver.
+     */
+
+    ret = pciDeviceIsBehindSwitchLackingACS(conn, dev);
+    if (ret < 0)
+        return 0;
+
+    if (ret) {
+        if (!strict_acs_check) {
+            VIR_DEBUG("%s %s: strict ACS check disabled; device assignment allowed",
+                      dev->id, dev->name);
+        } else {
+            pciReportError(conn, VIR_ERR_NO_SUPPORT,
+                           _("Device %s is behind a switch lacking ACS and "
+                             "cannot be assigned"),
+                           dev->name);
+            return 0;
+        }
+    }
+
+    return 1;
+}

src/util/pci.h

@@ -78,4 +78,8 @@ int pciDeviceFileIterate(virConnectPtr conn,
                          pciDeviceFileActor actor,
                          void *opaque);
 
+int pciDeviceIsAssignable(virConnectPtr conn,
+                          pciDevice *dev,
+                          int strict_acs_check);
+
 #endif /* __VIR_PCI_H__ */