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Re: [libvirt] [PATCH v2] qemu: Do not reattach PCI device used by other domain when shutdown



On 10/12/2011 10:05 PM, Osier Yang wrote:
When failing on starting a domain, it tries to reattach all the PCI
devices defined in the domain conf, regardless of whether the devices
are still used by other domain. This will cause the devices to be deleted
from the list qemu_driver->activePciHostdevs, thus the devices will be
thought as usable even if it's not true. And following commands
nodedev-{reattach,reset} will be successful.

How to reproduce:
   1) Define two domains with same PCI device defined in the confs.
   2) # virsh start domain1
   3) # virsh start domain2
   4) # virsh nodedev-reattach $pci_device

This time around, I actually spent time reproducing the bug scenario on hardware rather than just analyzing by inspection (it took me a while to figure out why the same machine that used to let me do pci passthrough was no longer working, until I realized that my hardware is old enough to be insecure, and I've upgraded software since my last passthrough test, so the CVE fix from https://bugzilla.redhat.com/show_bug.cgi?id=715555 has to be intentionally bypassed for me to get passthrough again). With that testing, I proved that this patch prevents that problem. But, as written, your patch caused the dreaded "An error occurred, but the cause is unknown".


You will see the device will be reattached to host successfully.
As pciDeviceReattach just check if the device is still used by
other domain via checking if the device is in list driver->activePciHostdevs,
however, the device is deleted from the list by step 2).

This patch is to prohibit the bug by:
   1) Prohibit a domain starting or device attachment right at
      preparation period (qemuPrepareHostdevPCIDevices) if the
      device is in list driver->activePciHostdevs, which means
      it's used by other domain.

   2) Introduces a new field for struct _pciDevice, (const char *used_by),
      it will be set as the domain name at preparation period,
      (qemuPrepareHostdevPCIDevices). Thus we can prohibit deleting
      the device from driver->activePciHostdevs if it's still used by
      other domain when stopping the domain process.


@@ -111,7 +112,7 @@ int qemuPrepareHostdevPCIDevices(struct qemud_driver *driver,
      if (!(pcidevs = qemuGetPciHostDeviceList(hostdevs, nhostdevs)))
          return -1;

-    /* We have to use 4 loops here. *All* devices must
+    /* We have to use 6 loops here. *All* devices must
       * be detached before we reset any of them, because
       * in some cases you have to reset the whole PCI,
       * which impacts all devices on it. Also, all devices

I added further loop labels.

+        /* The device is in use by other active domain if
+         * the dev is in list driver->activePciHostdevs.
+         */
+        if (!pciDeviceIsAssignable(dev, !driver->relaxedACS) ||
+            pciDeviceListFind(driver->activePciHostdevs, dev))
+            goto cleanup;
+    }

Here's where the bad message comes in - you jump to cleanup without ever emitting an error message. Not to mention now that we have the new used_by field, the message could actually be informative :) With my changes below, I get the much nicer:

Error starting domain: Requested operation is not valid: PCI device 0000:0a:0a.0 is in use by domain dom

@@ -277,6 +298,18 @@ void qemuDomainReAttachHostdevDevices(struct qemud_driver *driver,

      for (i = 0; i<  pciDeviceListCount(pcidevs); i++) {
          pciDevice *dev = pciDeviceListGet(pcidevs, i);
+        pciDevice *activeDev = NULL;
+        const char *used_by = NULL;
+
+        /* Never delete the dev from list driver->activePciHostdevs
+         *  if it's used by other domain.
+         */
+        activeDev = pciDeviceListFind(driver->activePciHostdevs, dev);
+        if (activeDev&&
+            (used_by = pciDeviceGetUsedBy(activeDev))&&
+            STRNEQ(name, used_by))
+            continue;


used_by is kept as it might be NULL.


In that case, use STRNEQ_NULLABLE. But you are right - across libvirtd restarts, we lose track of which domain owns the device - so I did indeed reproduce a case of NULL. Perhaps food for a later patch (when reloading domains, cycle through all hostdevs in use by active domains to repopulate the used_by fields). But not a show-stopper to getting this bug fix in now.

Well, I did find one other problem with a libvirtd restart - as soon as used_by is NULL, then stopping the domain that was actually using the device no longer frees that device out of the driver->active list (since we now only free if used_by matches) - so maybe it's important to fix libvirtd reload repopulating used_by sooner rather than later.

@@ -1312,6 +1313,7 @@ pciGetDevice(unsigned domain,
      dev->bus      = bus;
      dev->slot     = slot;
      dev->function = function;
+    dev->used_by  = NULL;

Pointless, since VIR_ALLOC 0-initializes.


      if (snprintf(dev->name, sizeof(dev->name), "%.4x:%.2x:%.2x.%.1x",
                   dev->domain, dev->bus, dev->slot,
@@ -1374,6 +1376,7 @@ pciFreeDevice(pciDevice *dev)
      VIR_DEBUG("%s %s: freeing", dev->id, dev->name);
      pciCloseConfig(dev);
      VIR_FREE(dev->path);
+    dev->used_by = NULL;
      VIR_FREE(dev);

Pointless, since dev is freed in the next statement.

ACK with this squashed in, so I went ahead and pushed.

diff --git i/src/libvirt_private.syms w/src/libvirt_private.syms
index 4673332..1e03e33 100644
--- i/src/libvirt_private.syms
+++ w/src/libvirt_private.syms
@@ -881,6 +881,7 @@ virNWFilterHashTableRemoveEntry;
 pciDettachDevice;
 pciDeviceFileIterate;
 pciDeviceGetManaged;
+pciDeviceGetName;
 pciDeviceGetUsedBy;
 pciDeviceIsAssignable;
 pciDeviceIsVirtualFunction;
diff --git i/src/qemu/qemu_hostdev.c w/src/qemu/qemu_hostdev.c
index f354ea8..c82c512 100644
--- i/src/qemu/qemu_hostdev.c
+++ w/src/qemu/qemu_hostdev.c
@@ -1,7 +1,7 @@
 /*
  * qemu_hostdev.c: QEMU hostdev management
  *
- * Copyright (C) 2006-2007, 2009-2010 Red Hat, Inc.
+ * Copyright (C) 2006-2007, 2009-2011 Red Hat, Inc.
  * Copyright (C) 2006 Daniel P. Berrange
  *
  * This library is free software; you can redistribute it and/or
@@ -119,21 +119,40 @@ int qemuPrepareHostdevPCIDevices(struct qemud_driver *driver,
      * must be reset before being marked as active.
      */

-    /* XXX validate that non-managed device isn't in use, eg
+    /* Loop 1: validate that non-managed device isn't in use, eg
      * by checking that device is either un-bound, or bound
      * to pci-stub.ko
      */

     for (i = 0; i < pciDeviceListCount(pcidevs); i++) {
         pciDevice *dev = pciDeviceListGet(pcidevs, i);
+        pciDevice *other;
+
+        if (!pciDeviceIsAssignable(dev, !driver->relaxedACS)) {
+            qemuReportError(VIR_ERR_OPERATION_INVALID,
+                            _("PCI device %s is not assignable"),
+                            pciDeviceGetName(dev));
+            goto cleanup;
+        }
         /* The device is in use by other active domain if
          * the dev is in list driver->activePciHostdevs.
          */
-        if (!pciDeviceIsAssignable(dev, !driver->relaxedACS) ||
-            pciDeviceListFind(driver->activePciHostdevs, dev))
+        if ((other = pciDeviceListFind(driver->activePciHostdevs, dev))) {
+            const char *other_name = pciDeviceGetUsedBy(other);
+
+            if (other_name)
+                qemuReportError(VIR_ERR_OPERATION_INVALID,
+                                _("PCI device %s is in use by domain %s"),
+                                pciDeviceGetName(dev), other_name);
+            else
+                qemuReportError(VIR_ERR_OPERATION_INVALID,
+                                _("PCI device %s is already in use"),
+                                pciDeviceGetName(dev));
             goto cleanup;
+        }
     }

+    /* Loop 2: detach managed devices */
     for (i = 0; i < pciDeviceListCount(pcidevs); i++) {
         pciDevice *dev = pciDeviceListGet(pcidevs, i);
         if (pciDeviceGetManaged(dev) &&
@@ -141,15 +160,15 @@ int qemuPrepareHostdevPCIDevices(struct qemud_driver *driver,
             goto reattachdevs;
     }

-    /* Now that all the PCI hostdevs have be dettached, we can safely
-     * reset them */
+    /* Loop 3: Now that all the PCI hostdevs have been detached, we
+     * can safely reset them */
     for (i = 0; i < pciDeviceListCount(pcidevs); i++) {
         pciDevice *dev = pciDeviceListGet(pcidevs, i);
         if (pciResetDevice(dev, driver->activePciHostdevs, pcidevs) < 0)
             goto reattachdevs;
     }

-    /* Now mark all the devices as active */
+    /* Loop 4: Now mark all the devices as active */
     for (i = 0; i < pciDeviceListCount(pcidevs); i++) {
         pciDevice *dev = pciDeviceListGet(pcidevs, i);
         if (pciDeviceListAdd(driver->activePciHostdevs, dev) < 0) {
@@ -158,8 +177,8 @@ int qemuPrepareHostdevPCIDevices(struct qemud_driver *driver,
         }
     }

- /* Now set the used_by_domain of the device in driver->activePciHostdevs
-     * as domain name.
+    /* Loop 5: Now set the used_by_domain of the device in
+     * driver->activePciHostdevs as domain name.
      */
     for (i = 0; i < pciDeviceListCount(pcidevs); i++) {
         pciDevice *dev, *activeDev;
@@ -170,7 +189,7 @@ int qemuPrepareHostdevPCIDevices(struct qemud_driver *driver,
         pciDeviceSetUsedBy(activeDev, name);
     }

-    /* Now steal all the devices from pcidevs */
+    /* Loop 6: Now steal all the devices from pcidevs */
     while (pciDeviceListCount(pcidevs) > 0) {
         pciDevice *dev = pciDeviceListGet(pcidevs, 0);
         pciDeviceListSteal(pcidevs, dev);
@@ -299,15 +318,13 @@ void qemuDomainReAttachHostdevDevices(struct qemud_driver *driver,
     for (i = 0; i < pciDeviceListCount(pcidevs); i++) {
         pciDevice *dev = pciDeviceListGet(pcidevs, i);
         pciDevice *activeDev = NULL;
-        const char *used_by = NULL;

         /* Never delete the dev from list driver->activePciHostdevs
-         *  if it's used by other domain.
+         * if it's used by other domain.
          */
         activeDev = pciDeviceListFind(driver->activePciHostdevs, dev);
         if (activeDev &&
-            (used_by = pciDeviceGetUsedBy(activeDev)) &&
-            STRNEQ(name, used_by))
+            STRNEQ_NULLABLE(name, pciDeviceGetUsedBy(activeDev)))
             continue;

         pciDeviceListDel(driver->activePciHostdevs, dev);
diff --git i/src/util/pci.c w/src/util/pci.c
index 888784a..2bbb90c 100644
--- i/src/util/pci.c
+++ w/src/util/pci.c
@@ -1313,7 +1313,6 @@ pciGetDevice(unsigned domain,
     dev->bus      = bus;
     dev->slot     = slot;
     dev->function = function;
-    dev->used_by  = NULL;

     if (snprintf(dev->name, sizeof(dev->name), "%.4x:%.2x:%.2x.%.1x",
                  dev->domain, dev->bus, dev->slot,
@@ -1376,10 +1375,15 @@ pciFreeDevice(pciDevice *dev)
     VIR_DEBUG("%s %s: freeing", dev->id, dev->name);
     pciCloseConfig(dev);
     VIR_FREE(dev->path);
-    dev->used_by = NULL;
     VIR_FREE(dev);
 }

+const char *
+pciDeviceGetName(pciDevice *dev)
+{
+    return dev->name;
+}
+
 void pciDeviceSetManaged(pciDevice *dev, unsigned managed)
 {
     dev->managed = !!managed;
diff --git i/src/util/pci.h w/src/util/pci.h
index 640c6af..ab29c0b 100644
--- i/src/util/pci.h
+++ w/src/util/pci.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2009 Red Hat, Inc.
+ * Copyright (C) 2009, 2011 Red Hat, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -39,6 +39,7 @@ pciDevice *pciGetDevice      (unsigned       domain,
                               unsigned       slot,
                               unsigned       function);
 void       pciFreeDevice     (pciDevice     *dev);
+const char *pciDeviceGetName (pciDevice     *dev);
int pciDettachDevice (pciDevice *dev, pciDeviceList *activeDevs); int pciReAttachDevice (pciDevice *dev, pciDeviceList *activeDevs);
 int        pciResetDevice    (pciDevice     *dev,


--
Eric Blake   eblake redhat com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org


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