[libvirt] [PATCH v2 2/2] check IOMMU group devices usage when preparing device for vfio passthrough

[Michal Privoznik]

On 14.01.2015 12:03, Shivaprasad G Bhat wrote:
> The virsh start <domain> fails with qemu error when the hostdevices of the
> same iommu group are used actively by other vms. It is not clear which
> hostdev from the same iommu group is used by any of the running guests.
> User has to go through every guest xml to figure out who is using the
> hostdev of same iommu group.
> 
> Solution:
> Iterate the iommu group of the hostdev and error our neatly in case a
> device in the same iommu group is busy. Reattach code also does the same
> kind of check, remove duplicate code as well.
> 
> Signed-off-by: Shivaprasad G Bhat <sbhat at linux.vnet.ibm.com>
> ---
>  src/util/virhostdev.c |   89 ++++++++++++++++++++++++++++++-------------------
>  1 file changed, 55 insertions(+), 34 deletions(-)
> 
> diff --git a/src/util/virhostdev.c b/src/util/virhostdev.c
> index 18ff96b..78deeba 100644
> --- a/src/util/virhostdev.c
> +++ b/src/util/virhostdev.c
> @@ -54,6 +54,41 @@ static virClassPtr virHostdevManagerClass;
>  static void virHostdevManagerDispose(void *obj);
>  static virHostdevManagerPtr virHostdevManagerNew(void);
>  
> +static int virHostdevIsPCINodeDeviceUsed(virPCIDeviceAddressPtr devAddr, void *opaque)
> +{
> +    virPCIDevicePtr other;
> +    int ret = -1;
> +    virPCIDevicePtr pci = NULL;
> +    virHostdevManagerPtr hostdev_mgr = opaque;
> +
> +    if (!(pci = virPCIDeviceNew(devAddr->domain, devAddr->bus,
> +                                devAddr->slot, devAddr->function)))
> +        goto cleanup;
> +
> +    other = virPCIDeviceListFind(hostdev_mgr->activePCIHostdevs, pci);
> +    if (other) {
> +        const char *other_drvname = NULL;
> +        const char *other_domname = NULL;
> +        virPCIDeviceGetUsedBy(other, &other_drvname, &other_domname);
> +
> +        if (other_drvname && other_domname)
> +            virReportError(VIR_ERR_OPERATION_INVALID,
> +                           _("PCI device %s is in use by "
> +                             "driver %s, domain %s"),
> +                           virPCIDeviceGetName(pci),
> +                           other_drvname, other_domname);
> +        else
> +            virReportError(VIR_ERR_OPERATION_INVALID,
> +                           _("PCI device %s is in use"),
> +                           virPCIDeviceGetName(pci));
> +        goto cleanup;
> +    }
> +    ret = 0;
> + cleanup:
> +    virPCIDeviceFree(pci);
> +    return ret;
> +}
> +
>  static int virHostdevManagerOnceInit(void)
>  {
>      if (!(virHostdevManagerClass = virClassNew(virClassForObject(),
> @@ -494,6 +529,7 @@ virHostdevPreparePCIDevices(virHostdevManagerPtr hostdev_mgr,
>      int last_processed_hostdev_vf = -1;
>      size_t i;
>      int ret = -1;
> +    virPCIDeviceAddressPtr devAddr = NULL;
>  
>      if (!nhostdevs)
>          return 0;
> @@ -518,7 +554,6 @@ virHostdevPreparePCIDevices(virHostdevManagerPtr hostdev_mgr,
>  
>      for (i = 0; i < virPCIDeviceListCount(pcidevs); i++) {
>          virPCIDevicePtr dev = virPCIDeviceListGet(pcidevs, i);
> -        virPCIDevicePtr other;
>          bool strict_acs_check = !!(flags & VIR_HOSTDEV_STRICT_ACS_CHECK);
>  
>          if (!virPCIDeviceIsAssignable(dev, strict_acs_check)) {
> @@ -528,23 +563,19 @@ virHostdevPreparePCIDevices(virHostdevManagerPtr hostdev_mgr,
>              goto cleanup;
>          }
>          /* The device is in use by other active domain if
> -         * the dev is in list activePCIHostdevs.
> +         * the dev is in list activePCIHostdevs. VFIO devices
> +         * belonging to same iommu group cant be shared
> +         * across guests.
>           */
> -        if ((other = virPCIDeviceListFind(hostdev_mgr->activePCIHostdevs, dev))) {
> -            const char *other_drvname;
> -            const char *other_domname;
> -
> -            virPCIDeviceGetUsedBy(other, &other_drvname, &other_domname);
> -            if (other_drvname && other_domname)
> -                virReportError(VIR_ERR_OPERATION_INVALID,
> -                               _("PCI device %s is in use by "
> -                                 "driver %s, domain %s"),
> -                               virPCIDeviceGetName(dev),
> -                               other_drvname, other_domname);
> -            else
> -                virReportError(VIR_ERR_OPERATION_INVALID,
> -                               _("PCI device %s is already in use"),
> -                               virPCIDeviceGetName(dev));
> +        if (STREQ(virPCIDeviceGetStubDriver(dev), "vfio-pci")) {
> +            devAddr = virPCIDeviceGetAddress(dev);
> +            if (!devAddr)
> +                goto cleanup;
> +            if (virPCIDeviceAddressIOMMUGroupIterate(devAddr,
> +                                                     virHostdevIsPCINodeDeviceUsed,
> +                                                     hostdev_mgr) < 0)
> +                goto cleanup;
> +        } else if (virHostdevIsPCINodeDeviceUsed(devAddr, hostdev_mgr)) {

This isn't gonna fly really. I mean, imagine this is the first iteration
and the stub driver for the device is not vfio-pci. So we end up here,
with devAddr being NULL. And virHostdevIsPCINodeDeviceUsed will
dereference it immediately. Moreover, if we have two devices on the
list, both with vfio-pci stub driver, on the first iteration, devAddr
will be allocated. However, on the next iteration, devAddr is allocated
again(!) without it being freed previously. And I'm not mentioning the
case where in the first iteration we go with vfio-pci branch and then,
in later iteration we go by the else branch (where devAddr would refer
to different device obviously).

Fortunately, there's just a small change required: allocate devAddr
unconditionally and free it when no longer needed. I'll fix it when
pushing. But next time - the crasher was caught by our test suite too:
virhostdevtest. If you ran 'make check' you'd see it.

>              goto cleanup;
>          }
>      }
> @@ -678,6 +709,7 @@ virHostdevPreparePCIDevices(virHostdevManagerPtr hostdev_mgr,
>      virObjectUnlock(hostdev_mgr->activePCIHostdevs);
>      virObjectUnlock(hostdev_mgr->inactivePCIHostdevs);
>      virObjectUnref(pcidevs);
> +    VIR_FREE(devAddr);
>      return ret;
>  }
>  
> @@ -1506,29 +1538,17 @@ int
>  virHostdevPCINodeDeviceReAttach(virHostdevManagerPtr hostdev_mgr,
>                                  virPCIDevicePtr pci)
>  {
> -    virPCIDevicePtr other;
> +    virPCIDeviceAddressPtr devAddr = NULL;
>      int ret = -1;
>  
>      virObjectLock(hostdev_mgr->activePCIHostdevs);
>      virObjectLock(hostdev_mgr->inactivePCIHostdevs);
> -    other = virPCIDeviceListFind(hostdev_mgr->activePCIHostdevs, pci);
> -    if (other) {
> -        const char *other_drvname = NULL;
> -        const char *other_domname = NULL;
> -        virPCIDeviceGetUsedBy(other, &other_drvname, &other_domname);
>  
> -        if (other_drvname && other_domname)
> -            virReportError(VIR_ERR_OPERATION_INVALID,
> -                           _("PCI device %s is still in use by "
> -                             "driver %s, domain %s"),
> -                           virPCIDeviceGetName(pci),
> -                           other_drvname, other_domname);
> -        else
> -            virReportError(VIR_ERR_OPERATION_INVALID,
> -                           _("PCI device %s is still in use"),
> -                           virPCIDeviceGetName(pci));
> +    if (!(devAddr = virPCIDeviceGetAddress(pci)))
> +        goto out;
> +
> +    if (virHostdevIsPCINodeDeviceUsed(devAddr, hostdev_mgr))
>          goto out;
> -    }
>  
>      virPCIDeviceReattachInit(pci);
>  
> @@ -1540,6 +1560,7 @@ virHostdevPCINodeDeviceReAttach(virHostdevManagerPtr hostdev_mgr,
>   out:
>      virObjectUnlock(hostdev_mgr->inactivePCIHostdevs);
>      virObjectUnlock(hostdev_mgr->activePCIHostdevs);
> +    VIR_FREE(devAddr);
>      return ret;
>  }
>  

Fixed and ACKed.

Michal