Ubuntu18.04 - KVM on S390 - Multiple epoch facility bugs

[bugproxy]

The bionic 4.15 kernel contains KVM/s390 support for the multiple epoch facility.
This code has some bugs which can result in hanging guests when running the guest on a z14 with a recent guest kernel (containing 6e2ef5e4f6cc57344762932d70d38ba4ec65fa8b s390/time: add support for the TOD clock epoch extension)

The following upstream commits are necessary to fix the multi epoch facility
0e7def5fb0dc KVM: s390: provide only a single function for setting the tod (fix SCK)
1575767ef3cf KVM: s390: consider epoch index on TOD clock syncs
d16b52cb9cdb KVM: s390: consider epoch index on hotplugged CPUs
5fe01793dd95 KVM: s390: take care of clock-comparator sign control

As an alternative 4.15.8 also contains these fixes.

---uname output---
4.15

---Additional Hardware Info---
Z14 LPAR

Machine Type = IBM z14

---System Hang---
A simple test case to trigger the hang of guests:

qemu-system-s390x -drive file=/data/bionic-server-s390x.iso,if=none,id=d1 -nographic -enable-kvm -device virtio-scsi-ccw -device scsi-cd,drive=d1 -m 1G -cpu z14,mepoch=on

it hangs
just before printing the network dialog.

[Frank Heimes (fheimes)]

upstream mainline kernel:
$ git tag --contains 0e7def5fb0dc
v4.16-rc4
v4.16-rc5
$ git tag --contains 1575767ef3cf
v4.16-rc4
v4.16-rc5
$ git tag --contains d16b52cb9cdb
v4.16-rc4
v4.16-rc5
$ git tag --contains 5fe01793dd95
v4.16-rc4
v4.16-rc5

[bugproxy (bugproxy)]

------- Comment From <email address hidden> 2018-03-14 05:11 EDT-------
FWIW, in case Ubuntu updates the kernel tree from 4.15.7 to 4.15.8 you will get these patches for free.

[Joseph Salisbury (jsalisbury)]

The Bionic master-next branch now has the 4.15.8 updates.

[bugproxy (bugproxy)]

------- Comment From <email address hidden> 2018-04-17 08:52 EDT-------
I can confirm that the testcase now works with the latest bionic snapshot:
# uname -a
Linux s35lp74 4.15.0-15-generic #16-Ubuntu SMP Wed Apr 4 13:57:26 UTC 2018 s390x s390x s390x GNU/Linux

Problem is fixed.

[Frank Heimes (fheimes)]

Thx for the confirmation 'cborntra'.
Changing ticket status to Fix Released.