[SRU][F][H][I][PATCH 0/x] KVM hardware diagnose data improvements for guest kernel (LP: 1953334)

[frank.heimes at canonical.com]

BugLink: https://bugs.launchpad.net/bugs/1953334

SRU Justification:

[Impact]

* Hardware diagnose data (diag 318) of KVM guest kernel cannot be handled.

* A fix is needed to enhance problem determination of guest kernel under KVM
  using DIAG 0x318 instruction execution.

* The s390x diagnose 318 instruction sets the control program name code (CPNC)
  and control program version code (CPVC) to provide useful information
  regarding the OS during debugging.

* The CPNC is explicitly set to 4 to indicate a Linux/KVM environment.

[Fix]

* In general the following 4 commits are needed:

* 3fd8417f2c728d810a3b26d7e2008012ffb7fd01 3fd8417f2c72 "KVM: s390: add debug statement for diag 318 CPNC data"
  https://launchpadlibrarian.net/572621875/0004-KVM-s390-add-debug-statement-for-diag-318-CPNC-data.patch

* 6cbf1e960fa52e4c63a6dfa4cda8736375b34ccc 6cbf1e960fa5 "KVM: s390: remove diag318 reset code"
  https://launchpadlibrarian.net/572621873/0003-KVM-s390-remove-diag318-reset-code.patch

* 23a60f834406c8e3805328b630d09d5546b460c1 23a60f834406 "s390/kvm: diagnose 0x318 sync and reset"
  https://launchpadlibrarian.net/572621869/0002-s390-kvm-diagnose-0x318-sync-and-reset.patch

* a23816f3cdcbffe5dc6e8c331914b3f51b87c2f3 a23816f3cdcb "s390/setup: diag 318: refactor struct"
  https://launchpadlibrarian.net/572620815/0001-s390-setup-diag-318-refactor-struct.patch

* For jammy, hirsute and impish only the first commit is needed, the others are already in.

* For focal all 4 commits are needed, but since they do not apply cleanly on focal, the attached backports need to be used instead.

[Test Case]

* Setup an IBM Z or LinuxONE LPAR with Ubuntu Server as KVM host.

* And setup an Ubuntu KVM virtual on top.

* It can then be observed if the CPNC (diag318 data) has been successfully set
  by looking at the s390dbf messages for the KVM guest.

* The CPNC will always be 4 (denotes Linux environment).

* Another way to test this is by running the sync_regs_test under
  tools/testing/selftests/kvm/s390x/sync_regs_test.
  Just running the kernel self test suite can trigger this.

[Where problems could occur]

* The approach here is to provide additional debug and diagnose information on top.

* Hence even if the diag318 changes are broken,
  the existing functionality shouldn't be harmed.

* The changes themselves are relatively discernible and mostly introduce new structures.

* However, with the functional changes broken code could be introduced
  (e.g. due to erroneous pointer arithmetic for example)
  that does not compile or causes crashes.
  But this is what the test builds are for
  (https://launchpad.net/~fheimes/+archive/ubuntu/lp1953334).

* On top the diag318 diagnose data might not properly provided - maybe empty or wrong.
  Again that is what the test builds and the verification later is targeted at.

* Since diag318 is s390x specific, all the modifications touch s390x code only.
  (in arch/s390/kvm/ kvm-s390.c and vsie.c, arch/s390/kernel/setup.c,
   arch/s390/include/asm/ kvm_host.h, kvm.h and diag.h)
  At least no other other architecture will be affected.

* Well, there is one tiny bit of a common code change,
  but it's just a new define statement in include/uapi/linux/kvm.h
  ('#define KVM_CAP_S390_DIAG318 186')

[Other]

* Request was to add the patches to focal / 20.04,
  but to avoid potential regressions on upgrades,
  the patches need to be added to jammy, impish and hirsute, too.

* As mentioned above, Jammy, Hirsute and Impish includes almost everything needed,
  except 3fd8417f2c72 "KVM: s390: add debug statement for diag 318 CPNC data".

* Hence the SRU is for Focal, Jammy, Hirsute and Impish,
  but less invasive for Jammy, Hirsute and Impish,
  also because commit 3fd8417f2c72 can be cleanly cherry-picked form there.

* LP#1953338 is related to this bug and covers the qemu/KVM bits.

Collin Walling (4):
  s390/setup: diag 318: refactor struct
  s390/kvm: diagnose 0x318 sync and reset
  KVM: s390: remove diag318 reset code
  KVM: s390: add debug statement for diag 318 CPNC data

 arch/s390/include/asm/diag.h     |  6 ++----
 arch/s390/include/asm/kvm_host.h |  4 +++-
 arch/s390/include/uapi/asm/kvm.h |  7 +++++--
 arch/s390/kernel/setup.c         |  3 +--
 arch/s390/kvm/kvm-s390.c         | 10 +++++++++-
 arch/s390/kvm/vsie.c             |  1 +
 include/uapi/linux/kvm.h         |  1 +
 7 files changed, 22 insertions(+), 10 deletions(-)

-- 
2.25.1