[Qemu-devel] [RFCv2 00/12] Clean up compatibility mode handling

[David Gibson]

This series is a significant rework to how we handle CPU compatibility
modes on ppc.

 * Information about compatibility modes was previously open coded and
   scattered across a number of functions in both target-ppc and spapr
   code.  It's now brought together into a common table of
   compatibility modes.

 * There was significant conceptual confusion about what a
   compatibility mode means, and how it interacts with the machine
   type.  This cleans that up, clarifying that a compatibility mode
   (as an externally set option) only makes sense on machine types
   that don't permit the guest hypervisor privilege (i.e. 'pseries')

 * It was previously the user's (or management layer's) responsibility
   to determine compatibility of CPUs on either end for migration.
   This uses the compatibility modes to check that properly during an
   incoming migration.

 * Some ill-considered sanity checks broke migration from 2.6 to 2.7,
   due to some new instruction classes being added.  This should avoid
   a repeat of that problem for 2.8 (we may be able to backport a
   minimal subset to 2.7-stable to fix the existing problem).

Patches 1-3 are preliminary cleanups which could stand on their own.
Patches 4-12 are the compatibility mode cleanup proper.

So far, this has been mimimally tested.  There are quite a few
migration cases to check.  For example:

Basic:

1) Boot guest with -cpu host
        Should go into POWER8 compat mode after CAS
        Previously would have been raw mode

2) Boot guest with -machine pseries,max-cpu-compat=power7 -cpu host
        Should go into POWER7 compat mode

3) Boot guest with -cpu host,compat=power7
        Should act as (2), but print a warning

4) Boot guest via libvirt with power7 compat mode specified in XML
        Should act as (3), (2) once we fix libvirt

5) Hack guest to only advertise power7 compatibility, boot with -cpu host
        Should go into POWER7 compat mode after CAS

6) Hack guest to only advertise real PVRs
        Should remain in POWER8 raw mode after CAS

7) Hack guest to only advertise real PVRs
   Boot with -machine pseries,max-cpu-compat=power8
        Should fail at CAS time

8) Hack guest to only advertise power7 compatibility, boot with -cpu host
   Reboot to normal guest
        Should go to power7 compat mode after CAS of boot 1
        Should revert to raw mode on reboot
        SHould go to power8 compat mode after CAS of boot 2

Migration:

9) Boot guest with qemu-2.6 -machine pseries-2.6 -cpu host
   Migrate to qemu-2.8 -machine pseries-2.6 -cpu host
        Should work, end up running in power8 raw mode

10) Boot guest with qemu-2.7 -machine pseries-2.7 -cpu host
    Migrate to qemu-2.8 -machine pseries-2.7 -cpu host
        Should work, end up running in power8 raw mode

11) Boot guest with qemu-2.7 -machine pseries-2.7 -cpu host,compat=power7
    Migrate to qemu-2.8 -machine pseries-2.7 -cpu host,compat=power7
        Should work, be running in POWER7 compat after, but give warning like
        (3)

12) Boot guest with qemu-2.7 -machine pseries-2.7 -cpu host,compat=power7
    Migrate to qemu-2.8 -machine pseries-2.7,max-cpu-compat=power7 -cpu host
        Should work, be running in POWER7 compat after, no warning

13) Boot to SLOF with qemu-2.6 -machine pseries-2.6 -cpu host
    Migrate to qemu-2.8 -machine pseries-2.6 -cpu host
        ?

14) Boot to SLOF with qemu-2.7 -machine pseries-2.7 -cpu host
    Migrate to qemu-2.8 -machine pseries-2.7 -cpu host
        ?

15) Boot to SLOF with qemu-2.7 -machine pseries-2.7 -cpu host,compat=power7
    Migrate to qemu-2.8 -machine pseries-2.7 -cpu host,compat=power7
        ?

16) Boot to SLOF with qemu-2.7 -machine pseries-2.7 -cpu host,compat=power7
    Migrate to qemu-2.8 -machine pseries-2.7,max-cpu-compat=power7 -cpu host
        ?

17) Boot guest with qemu-2.6 -machine pseries-2.6 -cpu host
    Migrate to qemu-2.7.z -machine pseries-2.6 -cpu host
        Should work

18) Hack guest to only advertise power7 compatibility, boot with -cpu host
    Boot with qemu-2.8, migrate to qemu-2.8
        Should be in power7 compat mode after CAS on source, and still
        in power7 compat mode on destination

Changes since RFCv1:
  * Change CAS logic to prefer compatibility modes over raw mode
  * Simplified by giving up on half-hearted attempts to maintain
    backwards migration
  * Folded migration stream changes into a single patch
  * Removed some preliminary patches which are already merged

David Gibson (12):
  pseries: Always use core objects for CPU construction
  pseries: Make cpu_update during CAS unconditional
  ppc: Clean up and QOMify hypercall emulation
  ppc: Rename cpu_version to compat_pvr
  ppc: Rewrite ppc_set_compat()
  ppc: Rewrite ppc_get_compat_smt_threads()
  ppc: Validate compatibility modes when setting
  pseries: Rewrite CAS PVR compatibility logic
  ppc: Add ppc_set_compat_all()
  pseries: Move CPU compatibility property to machine
  pseries: Reset CPU compatibility mode
  ppc: Rework CPU compatibility testing across migration

 hw/ppc/spapr.c              | 158 ++++++++++++++++------------
 hw/ppc/spapr_cpu_core.c     |  85 ++++++++++-----
 hw/ppc/spapr_hcall.c        | 140 +++++++------------------
 hw/ppc/trace-events         |   2 +-
 include/hw/ppc/spapr.h      |  12 ++-
 target-ppc/Makefile.objs    |   2 +-
 target-ppc/compat.c         | 249 ++++++++++++++++++++++++++++++++++++++++++++
 target-ppc/cpu.h            |  49 +++++++--
 target-ppc/excp_helper.c    |  11 +-
 target-ppc/kvm.c            |   4 +-
 target-ppc/kvm_ppc.h        |   4 +-
 target-ppc/machine.c        |  87 ++++++++++++++--
 target-ppc/translate_init.c | 157 +++++++---------------------
 13 files changed, 607 insertions(+), 353 deletions(-)
 create mode 100644 target-ppc/compat.c

-- 
2.7.4