Performing verification for mantic.
I deployed mantic onto a bare metal server, with kernel 6.5.0-26-generic from
-updates.
I installed a KVM stack, synced a cloud image, and tested VM creation.
$ uvt-kvm create --cpu 4 --memory 4096 --disk 10 jammy-a release=jammy
arch=amd64
$ uvt-kvm ssh jammy-a
Welcome to Ubuntu 22.04.4 LTS (GNU/Linux 5.15.0-101-generic x86_64)
From there, I found the PID of the VM:
$ ps aux | grep qemu
libvirt+ 1799 107 1.5 9642380 1044752 ? Sl 03:21 0:38
/usr/bin/qemu-system-x86_64 -name guest=jammy-a,debug-threads=on -S -object
{"qom-ty
We run perf:
$ sudo perf top -p 1799
$ virsh console jammy-a
Connected to domain 'jammy-a'
Escape character is ^] (Ctrl + ])
[ 161.413890] BUG: unable to handle page fault for address: fffffe18cdb1c028
[ 161.419474] #PF: supervisor read access in kernel mode
[ 161.423707] #PF: error_code(0x0000) - not-present page
[ 161.427949] PGD 17ffca0[ 161.429508] BUG: unable to handle page fault for
address: fffffe18cdb1c028
[ 161.429513] #PF: supervisor read access in kernel mode
[ 161.429516] #PF: error_code(0x0000) - n
The VM suffers a page fault and crashes, and is not accessible over ssh.
$ uvt-kvm ssh jammy-a
(no response).
I then enabled -proposed, and installed 6.5.0-27-generic:
$ uname -rv
6.5.0-27-generic #28-Ubuntu SMP PREEMPT_DYNAMIC Thu Mar 7 18:21:00 UTC 2024
$ uvt-kvm create --cpu 4 --memory 4096 --disk 10 jammy-a release=jammy
arch=amd64
$ uvt-kvm ssh jammy-a
Welcome to Ubuntu 22.04.4 LTS (GNU/Linux 5.15.0-101-generic x86_64)
We get the pid of the VM:
$ ps aux | grep qemu
libvirt+ 1786 42.5 1.5 7960876 1022308 ? Sl 03:37 0:40
/usr/bin/qemu-system-x86_64 -name guest=jammy-a,debug-threads=on -S -object
{"qom-ty
We run perf:
$ sudo perf top -p 1786
This time, the VM does not crash, and stays running:
$ virsh console jammy-a
Connected to domain 'jammy-a'
Escape character is ^] (Ctrl + ])
jammy-a login:
jammy-a login:
We can also ssh to the VM just fine:
$ uvt-kvm ssh jammy-a
Welcome to Ubuntu 22.04.4 LTS (GNU/Linux 5.15.0-101-generic x86_64)
This is much better. The kernel in -proposed fixes the issue, happy to
mark verified for mantic.
** Tags removed: verification-needed-mantic-linux
** Tags added: verification-done-mantic-linux
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https://bugs.launchpad.net/bugs/2054218
Title:
kvm: Running perf against qemu processes results in page fault inside
guest
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