ACK: [SRU][B][PATCH 0/1] Ubuntu 18.04 kernel 4.15.0-194 crashes on IPL (LP: 1994601)

[Tim Gardner]

On 10/27/22 9:29 AM, frank.heimes at canonical.com wrote:
> BugLink: https://bugs.launchpad.net/bugs/1994601
> 
> SRU Justification:
> 
> [ Impact ]
> 
>   * Ubuntu 18.04 / bionic installations with latest kernel 4.15.0-194
>     are no longer able to IPL (boot) on IBM z14 or newer hardware.
> 
>   * This issue got introduced by upstream commit e4f74400308c
>     "s390/archrandom: simplify back to earlier design and initialize earlier"
>     that was SRUed to 18.04/bionic based on LP#1989625,
>     which made changes in the s390s IPL/boot area of kernel/arch/random.
> 
>   * The reason seems to be that the bad patch moves the decision about
>     if arch randomness is available to setup.c function setup_randomness().
>     This code uses a static_key s390_arch_random_available.
>     But in the Canonical kernel the initialization function
>     for the jump labels (where the static keys are based on)
>     jump_label_init() is called in generic start_kernel()
>     wheres in the upstream kernel the init function is
>     called early in setup_arch().
> 
>   * Reverting this commit from bionic master-next makes bionic systems
>     again bootable.
>     (https://launchpad.net/~fheimes/+archive/ubuntu/test/)
> 
> [ Test Plan ]
> 
>   * An IBM z14 or LinuxONE II or newer system is needed.
> 
>   * Now install latest bionic on that system - doesn't if it's on LPAR,
>     z/VM or KVM.
> 
>   * After the installation (an the trigger of the post install reboot),
>     the system will not come up.
> 
>   * To test a patched kernel with e4f74400308c can be tested in the
>     following way:
> 
>   * Install 18.04 GA and prevent it from doing any kernel updates.
> 
>   * Means, install in 'island' mode
>     or select in d-i 'Advanced Installation'
>     and explicitly choose '4.15.0-50 generic' to install.
> 
>   * That allows the system to come up and to update the kernel to
>     a modified one.
> 
>   * Then reboot and verify if the system comes up properly.
> 
> [ Where problems could occur ]
> 
>   * Problems could occur due to the fact that the commit
>     was not cleanly reversible because of minor context changes.
> 
>   * Adjustments that were needed might break other things if not
>     done carefully.
> 
>   * Further commits (applied after e4f74400308c) may still rely
>     on the bad e4f74400308c commit - or even further patches
>     (from upstream stable).
> 
>   * In worst case IPL / boot might get broken,
>     even on hardware older than z14.
> 
>   * If the revert works fine can be easily tested and was tested based on
>     https://launchpad.net/~fheimes/+archive/ubuntu/test/
>     and the above test plan.
> 
> [ Other Info ]
>   
>   * Ubuntu 20.04 (focal, using legacy image with virt-install)
>     was tested as well, but is not affected by this issue.
> 
> Frank Heimes (1):
>    Revert "s390/archrandom: simplify back to earlier design and
>      initialize earlier"
> 
>   arch/s390/crypto/arch_random.c     | 111 ++++++++++++++++++++++++++++-
>   arch/s390/include/asm/archrandom.h |  27 +++----
>   arch/s390/kernel/setup.c           |   5 --
>   3 files changed, 121 insertions(+), 22 deletions(-)
> 
Acked-by: Tim Gardner <tim.gardner at canonical.com>
-- 
-----------
Tim Gardner
Canonical, Inc