Thank you very much for the reply. Another question is try_get_page
returns -ENOMEM but kvm warning is bad address which should be EFAULT.
Why qemu prints error log says bad address?
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Hi Jiatong,
Thanks for emailing me, happy to answer questions anytime.
> 1. why linux-hwe-4.15.0 source code is used?
If you look closely at the oops in the description, the customer I was
working with was running:
4.15.0-106-generic #107~16.04.1-Ubuntu
This is the Xenial (16.04) HWE kernel.
Interestingly, I hit this warning log without enabling ksm
```console
# cat /sys/kernel/mm/ksm/run
0
# uname -a
Linux compute12 4.15.0-72-generic #81-Ubuntu SMP Tue Nov 26 12:20:02 UTC 2019
x86_64 x86_64 x86_64 GNU/Linux
# lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Descri
This bug was fixed in the package linux - 5.4.0-48.52
---
linux (5.4.0-48.52) focal; urgency=medium
* focal/linux: 5.4.0-48.52 -proposed tracker (LP: #1894654)
* mm/slub kernel oops on focal kernel 5.4.0-45 (LP: #1895109)
- SAUCE: Revert "mm/slub: fix a memory leak in sysfs_s
This bug was fixed in the package linux - 4.15.0-118.119
---
linux (4.15.0-118.119) bionic; urgency=medium
* bionic/linux: 4.15.0-118.119 -proposed tracker (LP: #1894697)
* Packaging resync (LP: #1786013)
- update dkms package versions
* Introduce the new NVIDIA 450-server
As promised, I have an update on the lab machine I left running
ksm_refcnt_overflow.sh for a week straight.
The machine was running 4.15.0-116-generic from -proposed:
$ uname -rv
4.15.0-116-generic #117-Ubuntu SMP Fri Aug 28 16:04:22 UTC 2020
$ uptime
04:36:14 up 7 days, 1 min, 1 user, load av
As requested by the kernel team (in https://lists.ubuntu.com/archives
/kernel-team/2020-August/112775.html), I will do some additional testing
for this SRU to really make sure it won't cause any regressions.
I provisioned a lab machine on segmaas, running Bionic. I installed the
4.15.0-116-generic
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_re
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
This bug is awaiting verification that the kernel in -proposed solves
the problem. Please test the kernel and update this bug with the
results. If the problem is solved, change the tag 'verification-needed-
bionic' to 'verification-done-bionic'. If the problem still exists,
change the tag 'verifica
This bug is awaiting verification that the kernel in -proposed solves
the problem. Please test the kernel and update this bug with the
results. If the problem is solved, change the tag 'verification-needed-
focal' to 'verification-done-focal'. If the problem still exists, change
the tag 'verificati
** Changed in: linux (Ubuntu Bionic)
Status: In Progress => Fix Committed
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https://bugs.launchpad.net/bugs/1837810
Title:
KVM: Fix zero_page reference counter overfl
** Changed in: linux (Ubuntu Focal)
Status: In Progress => Fix Committed
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https://bugs.launchpad.net/bugs/1837810
Title:
KVM: Fix zero_page reference counter overflo
Attached is a kernel module which lets you see the contents of the
zero_page reference counter, and to set it to near overflow.
** Attachment added: "kernel module to view zero_page reference counter"
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1837810/+attachment/5402014/+files/zero_
Attached is a script to create and destroy VMs in a loop, to try and
increment the zero_page reference counter.
** Attachment added: "Reproducer script to create and destroy VMs"
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1837810/+attachment/5402013/+files/ksm_refcnt_overflow.sh
--
Thanks for fixing it @mruffell!
Yes, we did have KSM enabled on the hypervisor where we hit this issue.
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https://bugs.launchpad.net/bugs/1837810
Title:
KVM: Fix zero_page
** Summary changed:
- qemu instance gets paused with error: kvm run failed Bad address
+ KVM: Fix zero_page reference counter overflow when using KSM on KVM compute
host
** Description changed:
- We are occasionally running into the below qemu error on our Ubuntu16
- KVM hypervisors managed usi
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