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Bug 2132177

Summary: libvirt kills virtual machine on restart when 2M and 1G hugepages are mounted [rhel-8.6.0.z]
Product: Red Hat Enterprise Linux 8 Reporter: RHEL Program Management Team <pgm-rhel-tools>
Component: libvirtAssignee: Michal Privoznik <mprivozn>
Status: CLOSED ERRATA QA Contact: liang cong <lcong>
Severity: high Docs Contact:
Priority: high    
Version: 8.4CC: ailan, duclee, dzheng, jdenemar, jsuchane, mprivozn, virt-maint, yafu, yalzhang
Target Milestone: rcKeywords: Triaged, Upstream, ZStream
Target Release: ---Flags: pm-rhel: mirror+
Hardware: x86_64   
OS: Linux   
Whiteboard:
Fixed In Version: libvirt-8.0.0-5.5.module+el8.6.0+16828+96e76c36 Doc Type: Bug Fix
Doc Text:
Cause: When libvirt is restarted after a hugetlbfs was mounted and a guest is running, libvirt tries to create guest specific path in the new hugetlbfs mount point. Because of a bug in namespace code this fails which results in the guest being killed by libvirt. Consequence: Guest is killed on libvirtd restart. Fix: Twofold. Firstly, the namespace code was fixed so that creating this guest specific path now succeeds. Secondly, the creation is postponed until really needed (memory hotplug). Result: Guests can now survive libvirtd restart.
 Story Points: ---
Clone Of: 2123196 Environment:
Last Closed: 2022-10-25 09:32:39 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On: 2123196, 2151869    
Bug Blocks:    

Comment 5 liang cong 2022-10-09 06:34:03 UTC 
Find an issue on:
# rpm -q libvirt qemu-kvm
libvirt-8.0.0-5.5.module+el8.6.0+16828+96e76c36.x86_64
qemu-kvm-6.2.0-11.module+el8.6.0+16538+01ea313d.6.x86_64
which similar with scratch build on rhel8.7



1. Define a guest with below memorybacking xml.
  <memoryBacking>
    <hugepages>
      <page size='2048' unit='KiB'/>
    </hugepages>
  </memoryBacking>

2. Mount 1G hugepage path
mount -t hugetlbfs -o pagesize=1G hugetlbfs /dev/hugepages1G

3. Start vm
# virsh start vm1
Domain vm1 started

4. Prepare memory device hotplug xml like below:
# cat dimm1G.xml 
<memory model='dimm'>
    <source>
      <pagesize unit='KiB'>1048576</pagesize>
      <nodemask>0-1</nodemask>
    </source>
    <target>
      <size unit='KiB'>1048576</size>
      <node>0</node>
    </target>
  </memory>

# virsh attach-device vm1 dimm1G.xml 
error: Failed to attach device from dimm1G.xml
error: internal error: unable to execute QEMU command 'object-add': can't open backing store /dev/hugepages1G/libvirt/qemu/5-vm1 for guest RAM: Permission denied



@mprivozn could you help to check this issue?
Comment 6 liang cong 2022-10-09 09:27:58 UTC 
Additional info for comment#5
more info about reproduce steps could be seen at bug#2123196comment#34
Comment 7 liang cong 2022-10-12 06:49:56 UTC 
Verified on below build:
# rpm -q libvirt qemu-kvm
libvirt-8.0.0-5.5.module+el8.6.0+16828+96e76c36.x86_64
qemu-kvm-6.2.0-11.module+el8.6.0+16538+01ea313d.6.x86_64

Verify steps:
1. Define a guest with below memorybacking xml.
  <memoryBacking>
    <hugepages>
      <page size='2048' unit='KiB'/>
    </hugepages>
  </memoryBacking>

2. Start the VM and stop libvirt

# virsh start vm1 && systemctl stop libvirtd
Domain vm1 started

Warning: Stopping libvirtd.service, but it can still be activated by:
  libvirtd.socket
  libvirtd-ro.socket
  libvirtd-admin.socket

3. Mount 1G hugepage path
mount -t hugetlbfs -o pagesize=1G hugetlbfs /dev/hugepages1G


4. Do virsh list and guest still in running state.

# virsh -r list --all
 Id   Name   State
----------------------
 16    vm1    running

# virsh -r list --all
 Id   Name   State
----------------------
 16    vm1    running

5. Prepare memory device hotplug xml like below:
# cat dimm1G.xml 
<memory model='dimm'>
    <source>
      <pagesize unit='KiB'>1048576</pagesize>
      <nodemask>0-1</nodemask>
    </source>
    <target>
      <size unit='KiB'>1048576</size>
      <node>0</node>
    </target>
  </memory>


6. Hotplug dimm memory device:
# virsh attach-device vm1 dimm1G.xml 
Device attached successfully

7. Prepare memory device with 2M hugepage source hotplug xml like below:
# cat dimm2M.xml 
<memory model='dimm'>
    <source>
      <pagesize unit='KiB'>2048</pagesize>
      <nodemask>0-1</nodemask>
    </source>
    <target>
      <size unit='KiB'>1048576</size>
      <node>0</node>
    </target>
  </memory>

8. Hotplug dimm memory device:
# virsh attach-device vm1 dimm2M.xml 
Device attached successfully


9. Shutoff vm
# virsh destroy vm1
Domain vm1 destroyed


10. Restart libvirtd
# systemctl restart libvirtd

11. Start vm
# virsh start vm1
Domain 'vm1' started


Also check the below scenarios:
Steps:
1. memory backing 2M guest vm start -> mount 1G path -> hotplug 1G dimm -> restart vm -> restart libvirtd -> hotplug 1G dimm
2. mount 1G path -> memory backing 2M guest vm start -> restart libvirtd -> hogplug 1G dimm -> restart libvirtd -> restart vm ->hogplug 1G dimm

Tested with these settings：remember_owner=1 or 0, no memory backing,1G memory backing, 1G hugepage path as /mnt/hugepages1G, memfd memory backing
Comment 8 liang cong 2022-10-12 06:53:27 UTC 
Additional info:
1. Restart libvirt after mount hugepage path.
2. Umount and mount hugepage path may cause another issue bug#2134009
Comment 12 errata-xmlrpc 2022-10-25 09:32:39 UTC 
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (virt:rhel and virt-devel:rhel bug fix update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2022:7122