On Wed, Apr 08, 2020 at 02:29:16PM -0600, Jim Fehlig wrote: > Hotplugging PCI devices to Xen PV guests is only possible if the > libxl_domain_build_info struct has the e820_host field enabled when the > guest is created. By default it is disabled but libxl will automatically > enable e820_host if the config contains one or more PCI devices, in which > case hotplugging additional PCI devices later works. > > According to xl.cfg(5) man page it is safe to unconditionally enable the > PV-only e820_host setting. Furthermore xen.git commits 414979ba85 and > f92337d949, which introduce the setting with a default of disabled, claim > the setting can be enabled or even removed "once the auto-ballooning of > guests with PCI devices works". Those commits are from May 2011 so I > think it is safe to say the issues have been resolved in the meantime. > Regardless, we should avoid exposing a Xen setting in libvirt that could > be removed later. Does this have any implications for live migration compatibility if you silently enable this for all guests ? In QEMU/KVM if you did this, it would be considered an ABI change and could break live migration of a guest launched on old libvirt, to a host running new libvirt. > > Signed-off-by: Jim Fehlig <jfehlig@xxxxxxxx> > --- > > See related thread on the ML > > https://www.redhat.com/archives/libvir-list/2020-April/msg00376.html > > > src/libxl/libxl_conf.c | 5 +++++ > tests/libxlxml2domconfigdata/basic-pv.json | 3 ++- > tests/libxlxml2domconfigdata/multiple-ip.json | 3 ++- > 3 files changed, 9 insertions(+), 2 deletions(-) *if* the live migration compatibility is not a problem, then Reviewed-by: Daniel P. Berrangé <berrange@xxxxxxxxxx> Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
