[Bug 1847806] Comment bridged from LTC Bugzilla

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------- Comment From mranweil at us.ibm.com 2019-10-15 10:04 EDT-------
>From Paul:

I added TCG support for mffsl, mffscrn, mffscrni, mffsce to QEMU, and I
think they will appear in QEMU 4.2, which is not yet released.

I found that the support for these instructions were missing because of
my efforts to test work I did for GLibC to use those instructions in
GLibC 2.30 and GLibC 2.31.  It appears that eoan has GLibC 2.30 and has
hit these instructions.

Everything I can find says that these instructions exist in DD1 and
later versions of POWER9.

> a) do you want us to switch the default emulated CPU to from
power9_v2.0 to power8_v2.0 (If so we need the answer asap)?

I'm not sure what the decision criteria is here, but I'll try to offer
some information below.

> b) are there known missing/bad instructions in P9-TCG that we should
fix by backporting changes?

Making some presumptions...you are looking for how to make QEMU work out
of the box for a ppc64el TCG guest.  I would hazard that there is some
risk to backporting the instructions to QEMU 4.0, but I can't quantify
that easily.  I think it would be low, but I'm really not that familiar
with the QEMU code base.

The other consideration is that if you switch the default, you've
perhaps solved the problem in the default case, but POWER9 support would
still be broken if somebody tries to use it.

It would seem like the most comprehensive solution is to backport.

BUT, I can't speak to whether there are other instructions missing
between QEMU 4.0 and 4.2. :-/ Maybe Leonardo can better speak to a
preferred path forward.

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https://bugs.launchpad.net/bugs/1847806

Title:
  eoan: ppc64el install on pseries-eoan VM fails to install

Status in The Ubuntu-power-systems project:
  Incomplete
Status in debian-installer package in Ubuntu:
  Invalid
Status in glibc package in Ubuntu:
  New
Status in qemu package in Ubuntu:
  Confirmed

Bug description:
  Using today's ppc64el server iso, I tried to install this on a
  pseries-eoan VM hosted on a large x86 desktop server and it failed to
  install.

  VM: 2GB memory, 20GB virtio qcow, CPUs: 2

  Installer options:
  Language: English
  Location: United Kingdom
  Detect keyboard layout? No
  Keyboard: English (UK)
  Keyboard Layout: English (UK)
  Hostname: ubuntu
  Full name for the new user: cking
  Username for your account: cking
  Choose a password for the new user: ************
  Re-enter password to verify: ************
  Partitioning method: Guided - use entire disk
  Select disk to partition: Virtual disk 1 (vda) - 21.5 GB Virtio Block Device
  Write the changes to discs? Yes

  Then installer stopped and I cannot progress. See the attached photo
  of the failure.

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