Verification steps for focal: Again, I made sure I can reproduce on the existing 5.4.0-42-generic kernel.
I copied ksm_refcnt_overflow.sh and zero_page_refcount.c to the VM, and built the kernel module, and inserted it into the kernel: $ sudo insmod zero_page_refcount.ko $ cat /proc/zero_page_refcount Zero Page Refcount: 0x1 or 1 >From there, I started running the ksm_refcnt_script.sh in another terminal. I checked to ensure VMs were running: $ virsh list Id Name State ---------------------------- 1 instance-0 running 2 instance-1 running 3 instance-2 running >From there, we can see the reference counter increment: $ cat /proc/zero_page_refcount Zero Page Refcount: 0x1bd9 or 7129 $ cat /proc/zero_page_refcount Zero Page Refcount: 0x1f9e or 8094 $ cat /proc/zero_page_refcount Zero Page Refcount: 0x1fb0 or 8112 >From there, I set the reference counter in an attempt to make it overflow: $ cat /proc/zero_page_refcount Zero Page Refcount: 0x7fffff15 or 2147483413 $ cat /proc/zero_page_refcount Zero Page Refcount: 0x80000000 or -2147483648 >From there, all vms became paused: $ virsh list Id Name State ---------------------------- 137 instance-0 paused 138 instance-1 paused 139 instance-2 paused We see the following oops in dmesg: https://paste.ubuntu.com/p/3Dc73k9VYy/ I then rebooted the machine, enabled -proposed and installed 5.4.0-46-generic. $ uname -rv 5.4.0-46-generic #50-Ubuntu SMP Fri Aug 28 15:33:36 UTC 2020 I rebooted, and built a new kernel module with the new headers, and inserted it into the running kernel: $ sudo insmod zero_page_refcount.ko [sudo] password for ubuntu: ubuntu@ubuntu:~/module$ cat /proc/zero_page_refcount Zero Page Refcount: 0x1 or 1 Again, I started the ksm_refcnt_overflow.sh script in another terminal, and checked to see that VMs were being created: $ virsh list Id Name State ---------------------------- 1 instance-0 running 2 instance-1 running When we check the value of the reference counter, it is still 1 and not incrementing: $ cat /proc/zero_page_refcount Zero Page Refcount: 0x1 or 1 $ cat /proc/zero_page_refcount Zero Page Refcount: 0x1 or 1 When I attempt to trigger overflow: $ cat /proc/zero_page_refcount_set Zero Page Refcount set to 0x1FFFFFFFFF000 $ cat /proc/zero_page_refcount Zero Page Refcount: 0x7fffff00 or 2147483392 $ cat /proc/zero_page_refcount Zero Page Refcount: 0x7fffff00 or 2147483392 We never overflow. The problem is fixed. Marking the bug as verified for focal. ** Tags removed: verification-needed-focal ** Tags added: verification-done-focal -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1837810 Title: KVM: Fix zero_page reference counter overflow when using KSM on KVM compute host To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1837810/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
