Re: [PATCH] qemu: allow migration of guest with mdev vGPU to VF vGPU

Ping. It would be nice to get this into the upcoming release. On 12/13/24 1:07 PM, Laine Stump wrote: > GPU vendors are moving away from using mdev to create virtual GPUs > towards using SRIOV VFs that are vGPUs. In both cases, once created > the vGPUs are assigned to guests via <hostdev> (i.e. VFIO device > assignment), and inside the guest the devices look identical, but mdev > vGPUs are located by QEMU/VFIO using a uuid, while VF vGPUs are > located with a PCI address. So although we generally require the > device on the source host to exactly match the device on the > destination host, in the case of mdev-created vGPU vs. VF vGPU > migration *can* potentially work, except that libvirt has a hard-coded > check that prevents us from even trying. > > This patch loosens up that check so that we will allow attempts to > migrate a guest from a source host that has mdev-created vGPUs to a > destination host that has VF vGPUs (and vice versa). The expectation > is that if this doesn't actually work then QEMU will fail and generate > an error that we can report. > > Based-on-patch-by: Zhiyi Guo <zhguo(a)redhat.com&gt; > Signed-off-by: Laine Stump <laine(a)redhat.com&gt; > --- > > Zhiyi's original patch removed the check for subsys type completely, > and this worked. My modified patch keeps the check in place, but > allows it to pass if the src type is pci and dst is mdev, or vice > versa. > > src/conf/domain_conf.c | 28 +++++++++++++++++++++------- > 1 file changed, 21 insertions(+), 7 deletions(-) > > diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c > index 4ad8289b89..9d5fda0469 100644 > --- a/src/conf/domain_conf.c > +++ b/src/conf/domain_conf.c > @@ -20647,13 +20647,27 @@ virDomainHostdevDefCheckABIStability(virDomainHostdevDef *src, > return false; > } > > - if (src->mode == VIR_DOMAIN_HOSTDEV_MODE_SUBSYS && > - src->source.subsys.type != dst->source.subsys.type) { > - virReportError(VIR_ERR_CONFIG_UNSUPPORTED, > - _("Target host device subsystem %1$s does not match source %2$s"), > - virDomainHostdevSubsysTypeToString(dst->source.subsys.type), > - virDomainHostdevSubsysTypeToString(src->source.subsys.type)); > - return false; > + if (src->mode == VIR_DOMAIN_HOSTDEV_MODE_SUBSYS) { > + virDomainHostdevSubsysType srcType = src->source.subsys.type; > + virDomainHostdevSubsysType dstType = dst->source.subsys.type; > + > + /* If the source and destination subsys types aren't the same, > + * then migration can't be supported, *except* that it might > + * be supported to migrate from subsys type 'pci' to 'mdev' > + * and vice versa. (libvirt can't know for certain whether or > + * not it will actually work, so we have to just allow it and > + * count on QEMU to provide us with an error if it fails) > + */ > + > + if (srcType != dstType > + && ((srcType != VIR_DOMAIN_HOSTDEV_SUBSYS_TYPE_PCI && srcType != VIR_DOMAIN_HOSTDEV_SUBSYS_TYPE_MDEV) > + || (dstType != VIR_DOMAIN_HOSTDEV_SUBSYS_TYPE_PCI && dstType != VIR_DOMAIN_HOSTDEV_SUBSYS_TYPE_MDEV))) { > + virReportError(VIR_ERR_CONFIG_UNSUPPORTED, > + _("Target host device subsystem type %1$s is not compatible with source subsystem type %2$s"), > + virDomainHostdevSubsysTypeToString(dstType), > + virDomainHostdevSubsysTypeToString(srcType)); > + return false; > + } > } > > if (!virDomainDeviceInfoCheckABIStability(src->info, dst->info))