[libvirt] [PATCH 0/3] Fix memlock limit during hotplug of mdev devices

[Eric Farman]

The routine qemuDomainGetMemLockLimitBytes() has a couple tests
to determine what the maximum limit of locked memory should be.
If I start a domain without any vfio stuff, /proc/$PID/limits says
the limit is 64KiB.  If I start a guest with a vfio-ccw hostdev,
the limit is now $GUEST_MEMORY + 1GiB.  It doesn't matter if I
have one hostdev or a thousand; it's always 1GiB more than the
configured amount of guest memory.

If I start a guest without any vfio devices, and hotplug that same
vfio-ccw hostdev, the limit remains at 64KiB and I start getting
I/O errors in the guest.  This makes sense, since some of the I/O
chains are long enough to exceed that page limit, and the host
starts throwing errors.

There is already code that adjusts this limit during the hotplug
of vfio-pci devices, so patch 1 refactors that code so that it
can be re-used on the mdev hotplug path in patch 3.

Patch 2, meanwhile, adds some cleanup that I think is missing in
the vfio-pci path, based on my read of the mdev path.

  $ grep locked /proc/83543/limits 
  Max locked memory         65536                65536                bytes     
  $ virsh attach-device guest scratch-ca8b.xml 
  Device attached successfully

  $ grep locked /proc/83543/limits 
  Max locked memory         3221225472           3221225472           bytes     


Eric Farman (3):
  qemu: Refactor the max memlock routine
  qemu: Reset the maximum locked memory on hotplug fail
  qemu: Adjust max memlock on mdev hotplug

 src/qemu/qemu_domain.c  | 30 ++++++++++++++++++++++++++++++
 src/qemu/qemu_domain.h  |  2 ++
 src/qemu/qemu_hotplug.c | 22 ++++++++++++----------
 3 files changed, 44 insertions(+), 10 deletions(-)

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2.17.1