[PATCH] qemu: don't reset PCI devices being assigned with VFIO

[Laine Stump <laine@xxxxxxxxx>]

I just learned that VFIO resets PCI devices when they are assigned to
guests / returned to the host, so it is redundant for libvirt to reset
the devices. This patch inhibits calling virPCIDeviceReset to devices
that will be/were assigned using VFIO.
---
 src/qemu/qemu_hostdev.c | 4 ++++
 src/qemu/qemu_hotplug.c | 5 +++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/qemu/qemu_hostdev.c b/src/qemu/qemu_hostdev.c
index 2b0221d..5a87eb0 100644
--- a/src/qemu/qemu_hostdev.c
+++ b/src/qemu/qemu_hostdev.c
@@ -556,6 +556,8 @@ int qemuPrepareHostdevPCIDevices(virQEMUDriverPtr driver,
      * can safely reset them */
     for (i = 0; i < virPCIDeviceListCount(pcidevs); i++) {
         virPCIDevicePtr dev = virPCIDeviceListGet(pcidevs, i);
+        if (STREQ_NULLABLE(virPCIDeviceGetStubDriver(dev), "vfio-pci"))
+            continue;
         if (virPCIDeviceReset(dev, driver->activePciHostdevs,
                               driver->inactivePciHostdevs) < 0)
             goto reattachdevs;
@@ -1122,6 +1124,8 @@ void qemuDomainReAttachHostdevDevices(virQEMUDriverPtr driver,
 
     for (i = 0; i < virPCIDeviceListCount(pcidevs); i++) {
         virPCIDevicePtr dev = virPCIDeviceListGet(pcidevs, i);
+        if (STREQ_NULLABLE(virPCIDeviceGetStubDriver(dev), "vfio-pci"))
+            continue;
         if (virPCIDeviceReset(dev, driver->activePciHostdevs,
                               driver->inactivePciHostdevs) < 0) {
             virErrorPtr err = virGetLastError();
diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c
index 18f5fa5..46875ad 100644
--- a/src/qemu/qemu_hotplug.c
+++ b/src/qemu/qemu_hotplug.c
@@ -2528,8 +2528,9 @@ qemuDomainDetachHostPciDevice(virQEMUDriverPtr driver,
     if (pci) {
         activePci = virPCIDeviceListSteal(driver->activePciHostdevs, pci);
         if (activePci &&
-            virPCIDeviceReset(activePci, driver->activePciHostdevs,
-                              driver->inactivePciHostdevs) == 0) {
+            (subsys->u.pci.backend == VIR_DOMAIN_HOSTDEV_PCI_BACKEND_VFIO ||
+             virPCIDeviceReset(activePci, driver->activePciHostdevs,
+                               driver->inactivePciHostdevs) == 0)) {
             qemuReattachPciDevice(activePci, driver);
             ret = 0;
         } else {
-- 
1.7.11.7

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