[Bug 1708305] [NEW] Realtime feature mlockall: Cannot allocate memory

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[Environment]

root at buneary:~# lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 16.04.2 LTS
Release:	16.04
Codename:	xenial

root at buneary:~# uname -r
4.10.0-29-generic

Reproducible also with the 4.4 kernel.

[Description]

When a guest memory backing stanza is defined using the <locked/> stanza + hugepages,
as follows:

  <memoryBacking>
    <hugepages>
      <page size='1' unit='GiB' nodeset='0'/>
      <page size='1' unit='GiB' nodeset='1'/>
    </hugepages>
    <nosharedpages/>
    <locked/>
  </memoryBacking>

(Full guest definition: http://paste.ubuntu.com/25229162/)

The guest fails to start due to the following error:

2017-08-02 20:25:03.714+0000: starting up libvirt version: 1.3.1, package: 1ubuntu10.12 (Christian Ehrhardt <christian.ehrhardt at canonical.com> Wed, 19 Jul 2017 08:28:14 +0200), qemu version: 2.5.0 (Debian 1:2.5+dfsg-5ubuntu10.14), hostname: buneary.seg
LC_ALL=C PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin QEMU_AUDIO_DRV=none /usr/bin/kvm-spice -name reproducer2 -S -machine pc-i440fx-2.5,accel=kvm,usb=off -cpu host -m 124928 -realtime mlock=on -smp 32,sockets=16,cores=1,threads=2 -object memory-backend-file,id=ram-node0,prealloc=yes,mem-path=/dev/hugepages/libvirt/qemu,share=yes,size=64424509440,host-nodes=0,policy=bind -numa node,nodeid=0,cpus=0-15,memdev=ram-node0 -object memory-backend-file,id=ram-node1,prealloc=yes,mem-path=/dev/hugepages/libvirt/qemu,share=yes,size=66571993088,host-nodes=1,policy=bind -numa node,nodeid=1,cpus=16-31,memdev=ram-node1 -uuid 2460778d-979b-4024-9a13-0c3ca04b18ec -no-user-config -nodefaults -chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/domain-reproducer2/monitor.sock,server,nowait -mon chardev=charmonitor,id=monitor,mode=control -rtc base=utc -no-shutdown -boot strict=on -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2 -drive file=/var/lib/uvtool/libvirt/images/test-ds.qcow,format=qcow2,if=none,id=drive-virtio-disk0,cache=none -device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x3,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1 -chardev pty,id=charserial0 -device isa-serial,chardev=charserial0,id=serial0 -vnc 127.0.0.1:0 -device cirrus-vga,id=video0,bus=pci.0,addr=0x2 -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x4 -msg timestamp=on
Domain id=14 is tainted: host-cpu
char device redirected to /dev/pts/1 (label charserial0)

mlockall: Cannot allocate memory

2017-08-02T20:25:37.732772Z qemu-system-x86_64: locking memory failed
2017-08-02 20:25:37.811+0000: shutting down

This seems to be due to the setrlimit for RLIMIT_MEMLOCK is too low for mlockall
to work given the large amount of memory.

There is a libvirt upstream patch that enforces the existence of the
hard_limit stanza when using with <locked/> in the memory backing settings.

https://github.com/libvirt/libvirt/commit/c2e60ad0e5124482942164e5fec088157f5e716a

Memory locking can only work properly if the memory locking limit
for the QEMU process has been raised appropriately: the default one
is extremely low, so there's no way the guest will fit in there.

The commit
https://github.com/libvirt/libvirt/commit/7e667664d28f90bf6916604a55ebad7e2d85305b
is also required when using hugepages and the locked stanza.


[Suggested Fix]

*
https://github.com/libvirt/libvirt/commit/c2e60ad0e5124482942164e5fec088157f5e716a

*
https://github.com/libvirt/libvirt/commit/7e667664d28f90bf6916604a55ebad7e2d85305b

** Affects: libvirt (Ubuntu)
     Importance: Medium
         Status: Fix Committed

** Affects: libvirt (Ubuntu Xenial)
     Importance: Medium
     Assignee: Jorge Niedbalski (niedbalski)
         Status: In Progress

** Affects: libvirt (Ubuntu Zesty)
     Importance: Medium
     Assignee: Jorge Niedbalski (niedbalski)
         Status: In Progress

** Affects: libvirt (Ubuntu Artful)
     Importance: Medium
         Status: Fix Committed


** Tags: canonical-bootstack libvirt-3.6 patch
-- 
Realtime feature mlockall: Cannot allocate memory
https://bugs.launchpad.net/bugs/1708305
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