Bug 2078693
| Summary: | libvirt can not identify shared memory after restarting virtqemud | ||
|---|---|---|---|
| Product: | Red Hat Enterprise Linux 9 | Reporter: | yafu <yafu> |
| Component: | libvirt | Assignee: | Ján Tomko <jtomko> |
| libvirt sub component: | General | QA Contact: | liang cong <lcong> |
| Status: | CLOSED ERRATA | Docs Contact: | Jiri Herrmann <jherrman> |
| Severity: | high | ||
| Priority: | high | CC: | dzheng, jdenemar, jherrman, jtomko, lizhu, lmen, nanli, smitterl, thuth, virt-maint, xuzhang, ymankad |
| Version: | 9.1 | Keywords: | Triaged |
| Target Milestone: | rc | ||
| Target Release: | 9.3 | ||
| Hardware: | Unspecified | ||
| OS: | Unspecified | ||
| Whiteboard: | |||
| Fixed In Version: | libvirt-9.2.0-1.el9 | Doc Type: | Bug Fix |
| Doc Text: |
.`virtiofs` devices could not be attached after restarting `virtqemud` or `libvirtd`
Previously, restarting the `virtqemud` or `libvirtd` services prevented `virtiofs` storage devices from being attached to virtual machines (VMs) on your host. This bug has been fixed, and you can now attach `virtiofs` devices in the described scenario as expected.
|
Story Points: | --- |
| Clone Of: | Environment: | ||
| Last Closed: | 2023-11-07 08:30:47 UTC | Type: | Bug |
| Regression: | --- | Mount Type: | --- |
| Documentation: | --- | CRM: | |
| Verified Versions: | Category: | --- | |
| oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |
| Cloudforms Team: | --- | Target Upstream Version: | 9.2.0 |
| Embargoed: | |||
Pushed upstream as:
commit d5c7b7870e45575f81fffcb611c2546d0e02e778
Author: Ján Tomko <jtomko>
CommitDate: 2023-03-14 17:10:01 +0100
qemu: relax shared memory check for vhostuser daemons
For some vhostuser daemons, we validate that the guest memory is shared
with the host.
With earlier versions of QEMU, it was only possible to mark memory
as shared by defining an explicit NUMA topology. Later, QEMU exposed
the name of the default memory backend (defaultRAMid) so we can mark
that memory as shared.
Since libvirt commit:
commit bff2ad5d6b1f25da02802273934d2a519159fec7
qemu: Relax validation for mem->access if guest has no NUMA
we already check for the case when user requests shared memory,
but QEMU did not expose defaultRAMid.
Drop the duplicit check from vhostuser device validation, to make
it pass on hotplug even after libvirtd restart.
This avoids the need to store the defaultRAMid, since we don't really
need it for anything after the VM has been already started.
https://bugzilla.redhat.com/show_bug.cgi?id=2078693
https://bugzilla.redhat.com/show_bug.cgi?id=2177701
Signed-off-by: Ján Tomko <jtomko>
Reviewed-by: Michal Privoznik <mprivozn>
git describe: v9.1.0-200-gd5c7b7870e
Preverified on upstream build: libvirt v9.1.0-248-g27d8bcc337
Test steps:
1.Start a guest with shared memory:
...
<memoryBacking>
<access mode='shared'/>
</memoryBacking>
...
2.Prepare a virtiofs device xml:
#cat fs.xml
<filesystem accessmode="passthrough" type="mount">
<driver queue="512" type="virtiofs"/>
<source dir="/var/tmp/mount_tag0"/>
<target dir="mount_tag0"/>
<alias name="ua-05e63df0-c4ab-11ec-ba3d-fa163ed3db7d"/>
<binary path="/usr/libexec/virtiofsd" xattr="on">
<cache mode="none"/>
<lock flock="off" posix="off"/>
</binary>
</filesystem>
3.Create the monut dir:
#mkdir /var/tmp/mount_tag0
4.Attach the device to the vm:
# virsh attach-device vm1 fs.xml
Device attached successfully
5.Detach virtiofs device from the vm:
# virsh detach-device vm1 fs.xml
Device detached successfully
6.Restart virtqemud:
#systemctl restart virtqemud
7.Attach virtiofs devcie to the vm again:
# virsh attach-device vm1 fs.xml
Device attached successfully
8. Detach virtiofs device from the vm again:
# virsh detach-device vm1 fs.xml
Device detached successfully
A similar ticket for RHEL8 can be found here: https://bugzilla.redhat.com/show_bug.cgi?id=2177701 Verified on upstream build:
# rpm -q libvirt qemu-kvm
libvirt-9.3.0-2.el9.x86_64
qemu-kvm-8.0.0-3.el9.x86_64
Test steps:
1.Start a guest with shared memory:
...
<memoryBacking>
<access mode='shared'/>
</memoryBacking>
...
2.Prepare a virtiofs device xml:
#cat fs.xml
<filesystem accessmode="passthrough" type="mount">
<driver queue="512" type="virtiofs"/>
<source dir="/var/tmp/mount_tag0"/>
<target dir="mount_tag0"/>
<alias name="ua-05e63df0-c4ab-11ec-ba3d-fa163ed3db7d"/>
<binary path="/usr/libexec/virtiofsd" xattr="on">
<cache mode="none"/>
<lock flock="off" posix="off"/>
</binary>
</filesystem>
3.Create the monut dir:
#mkdir /var/tmp/mount_tag0
4.Attach the device to the vm:
# virsh attach-device vm1 fs.xml
Device attached successfully
5.Detach virtiofs device from the vm:
# virsh detach-device vm1 fs.xml
Device detached successfully
6.Restart virtqemud:
#systemctl restart virtqemud
7.Attach virtiofs devcie to the vm again:
# virsh attach-device vm1 fs.xml
Device attached successfully
8. Detach virtiofs device from the vm again:
# virsh detach-device vm1 fs.xml
Device detached successfully
It's a per-VM issue. When starting the VM, libvirt probes the QEMU capabilities, including whether it exposes the alias of the default memory device. Libvirt uses the alias to tell QEMU to mark the guest memory as shared. For older QEMU/libvirt, other methods of creating shared memory are used: https://libvirt.org/kbase/virtiofs.html#other-options-for-vhost-user-memory-setup Libvirt does not save the memory alias in the VM's status XML. After daemon restart, the QEMU capabilities are not probed again, but read from the status XML. The bug here is that the validation required either a memory alias, or one of the alternate ways of having shared memory. The fix removed the requirement for a memory alias, because this is already validated at VM startup. The "workarounds" here are a) do not restart the daemon b) use a VM with one of the alternate setups of shared memory c) restart the VM to be able to hotplug a virtiofs <filesystem> However none of them are applicable if you already have a running VM and restarted the daemon. 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 (Moderate: libvirt security, bug fix, and enhancement 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/RHSA-2023:6409 |
Description of problem: libvirt can not identify shared memory after restarting virtqemud Version-Release number of selected component (if applicable): libvirt-8.2.0-1.el9.x86_64 How reproducible: 100% Steps to Reproduce: 1.Start a guest with shared memory: <domain> ... <memoryBacking> <access mode='shared'/> </memoryBacking> ... 2.Prepare a virtiofs device xml: #cat fs.xml <filesystem accessmode="passthrough" type="mount"> <driver queue="512" type="virtiofs"/> <source dir="/var/tmp/mount_tag0"/> <target dir="mount_tag0"/> <alias name="ua-05e63df0-c4ab-11ec-ba3d-fa163ed3db7d"/> <binary path="/usr/libexec/virtiofsd" xattr="on"> <cache mode="none"/> <lock flock="off" posix="off"/> </binary> </filesystem> 3.Create the monut dir: #mkdir /var/tmp/mount_tag0 4.Attach the device to the vm: # virsh attach-device avocado-vt-vm1 fs.xml Device attached successfully 5.Detach virtiofs device from the vm: # virsh detach-device avocado-vt-vm1 fs.xml Device detached successfully 6.Restart virtqemud: #systemctl restart virtqemud 7.Attach virtiofs devcie to the vm again: # virsh attach-device avocado-vt-vm1 fs.xml error: Failed to attach device from fs.xml error: unsupported configuration: 'virtiofs' requires shared memory 8.Check the live vm xml and qemu cmd line, shared memory still exists: #virsh dumpxml avocado-vt-vm1 <domain> ... <memoryBacking> <access mode='shared'/> </memoryBacking> ... #ps aux | grep shared qemu 267628 73.4 18.9 3534168 761076 ? Sl 03:00 1:36 /usr/bin/qemu-kvm -name guest=avocado-vt-vm1,debug-threads=on ... -m 2048 -object memory-backend-file,id=pc.ram,mem-path=/var/lib/libvirt/qemu/ram/6-avocado-vt-vm1/pc.ram,***share=on*** Actual results: libvirt can not identify shared memory after restarting virtqemud, so can not attach the virtiofs device to vm after restarting virtqemud Expected results: libvirt should always identify shared memory. Additional info: