Verification steps for Bionic: First, I made sure I could reproduce the problem on 4.15.0-115-generic.
I made a fresh Bionic VM, and copied over the ksm_refcnt_overflow.sh and zero_page_refcound.c files. I built the kernel module, and inserted it into the kernel. >From there, I checked the zero_page reference counter. $ sudo insmod zero_page_refcount.ko [sudo] password for ubuntu: ubuntu@ubuntu:~/module$ cat /proc/zero_page_refcount Zero Page Refcount: 0x1 or 1 >From there, in another terminal, I ran the script ksm_refcnt_overflow.sh, and checked to see VMs were running: $ virsh list Id Name State ---------------------------------------------------- 1 instance-0 running 2 instance-1 running 3 instance-2 running 4 instance-3 running 5 instance-4 running >From there, we can see the reference counter increment: $ cat /proc/zero_page_refcount Zero Page Refcount: 0x1158 or 4440 ubuntu@ubuntu:~/module$ cat /proc/zero_page_refcount Zero Page Refcount: 0x1622 or 5666 ubuntu@ubuntu:~/module$ cat /proc/zero_page_refcount Zero Page Refcount: 0x163a or 5690 I issued the set command, to get it ready to overflow: $ cat /proc/zero_page_refcount_set Zero Page Refcount set to 0x1FFFFFFFFF000 I then checked and saw it overflow: ubuntu@ubuntu:~/module$ cat /proc/zero_page_refcount Zero Page Refcount: 0x7fffff27 or 2147483431 ubuntu@ubuntu:~/module$ cat /proc/zero_page_refcount Zero Page Refcount: 0x7fffff92 or 2147483538 ubuntu@ubuntu:~/module$ cat /proc/zero_page_refcount Zero Page Refcount: 0x80000000 or -2147483648 Instances became paused, and virtualisation broken: $ virsh list Id Name State ---------------------------------------------------- 5 instance-4 paused 6 instance-5 paused 7 instance-6 paused 8 instance-7 paused 9 instance-0 paused 10 instance-1 paused 11 instance-2 paused 12 instance-3 paused >From there, we see the usual call trace in dmesg: https://paste.ubuntu.com/p/wpJkGCH3fJ/ I rebooted, and enabled -proposed. I then installed the 4.15.0-116-generic kernel, and rebooted again. I rebuilt the zero_page_refcount kernel module with the new headers, and inserted it into the running kernel. $ uname -rv 4.15.0-116-generic #117-Ubuntu SMP Fri Aug 28 16:04:22 UTC 2020 $ sudo insmod zero_page_refcount.ko ubuntu@ubuntu:~/module$ cat /proc/zero_page_refcount Zero Page Refcount: 0x1 or 1 >From there, I started the script ksm_refcnt_overflow.sh in another terminal. We can see that VMs are running: $ virsh list Id Name State ---------------------------------------------------- 1 instance-1 running 2 instance-2 running 3 instance-3 running 4 instance-4 running Checking the value of the zero_page reference counter: $ cat /proc/zero_page_refcount Zero Page Refcount: 0x1 or 1 We are still at 1. Now attempting 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 ubuntu@ubuntu:~/module$ cat /proc/zero_page_refcount Zero Page Refcount: 0x7fffff00 or 2147483392 ubuntu@ubuntu:~/module$ cat /proc/zero_page_refcount Zero Page Refcount: 0x7fffff00 or 2147483392 The reference counter is never incremented, and will not overflow. The problem is solved, and I am happy to mark this bug as verified for bionic. ** Tags removed: verification-needed-bionic ** Tags added: verification-done-bionic -- 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
