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Re: [libvirt] [PATCHv2 08/12] qemu: don't reset PCI devices being assigned with VFIO



On Tue, Jun 25, 2013 at 01:06:55PM -0400, Laine Stump wrote:
> On 06/25/2013 06:44 AM, Daniel P. Berrange wrote:
> > On Mon, Jun 24, 2013 at 11:05:34PM -0400, Laine Stump wrote:
> >> 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 dfe39c6..d7d54d7 100644
> >> --- a/src/qemu/qemu_hostdev.c
> >> +++ b/src/qemu/qemu_hostdev.c
> >> @@ -548,6 +548,8 @@ 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;
> >> @@ -1114,6 +1116,8 @@ 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)) {
> > I'm guessing that virPCIDeviceGetStubDriver() isn't returning 'pci-stub'
> > here, right ? Otherwise you'd would have used the same pattern as earlier
> 
> No, the stub driver should be set correctly at this time[*]. It was just
> a case of having multiple options for learning the answer in this case,
> and choosing the one that's more efficient.

Ok, so where I was going here, was that if the the virPCIDevicePtr
object has enough info, then could we make virPCIDeviceReset()
look for stub == vfio-pci, and make itself a nop. This avoids the
risk of one caller forgetting to do the check itself.


Daniel
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