[Bug 1835809] Re: AMD Ryzen 3000 series fails to boot

[Adam Conrad]

Hello Jeremy, or anyone else affected,

Accepted systemd into disco-proposed. The package will build now and be
available at https://launchpad.net/ubuntu/+source/systemd/240-6ubuntu5.2
in a few hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.  Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested and change the tag from
verification-needed-disco to verification-done-disco. If it does not fix
the bug for you, please add a comment stating that, and change the tag
to verification-failed-disco. In either case, without details of your
testing we will not be able to proceed.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance for helping!

N.B. The updated package will be released to -updates after the bug(s)
fixed by this package have been verified and the package has been in
-proposed for a minimum of 7 days.

** Changed in: systemd (Ubuntu Disco)
       Status: In Progress => Fix Committed

** Tags added: verification-needed verification-needed-disco

** Changed in: systemd (Ubuntu Disco)
     Assignee: (unassigned) => Balint Reczey (rbalint)

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https://bugs.launchpad.net/bugs/1835809

Title:
  AMD Ryzen 3000 series fails to boot

Status in systemd package in Ubuntu:
  In Progress
Status in systemd source package in Disco:
  Fix Committed

Bug description:
  [Impact]

   * Systems with AMD Ryzen 3000 series CPUs don't boot.

  [Test Case]

   * Boot with fixed systemd on an AMD Ryzen 3000 series system.

  [Regression Potential]

   * The fix itself is very small, it ignores known to be faulty random
  values returned by the rdrand instruction and use a different random
  source. Those values can still be returned by a properly working
  rdrand implementation in 2 in 2^32 cases on 32 bit arches and in 2 in
  2^64 cases on 64 bit arches, but the fallback to the other random
  source ensures that in those rare occasions a random number can be
  generated.

  [Original Bug Text]

  On the new AMD Ryzen 3000 series CPUs, there is an issue with systemd
  preventing the boot process from completing. This issue does not
  affect the older systemd version in 18.04, but affects the 19.04
  version.

  Here is a screenshot showing what happens:
  https://www.phoronix.net/image.php?id=ryzen-3700x-3900x-linux&image=amd_zen2_14_show

  I am currently testing a patch to systemd, derived from this pull request:
  https://github.com/systemd/systemd/pull/12536

  This is a high severity issue, as I do not believe there is no
  potential workaround without either a firmware update or an ISO
  respin.

  I have attached a rebase of the potential patch on the current 19.04
  version of systemd for reference. I will provide more details after
  testing.

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