[PATCH v4 for-5.2 0/2] spapr: Improve error reporting in spapr_caps.c

[Greg Kurz]

Nested KVM HV only works if the kernel is using the radix MMU mode, ie.
the CPU is POWER9 and it is not running in some pre-power9 compat mode.
Otherwise, the KVM HV module fails to load in the guest with -ENODEV.
It might be painful for a user to discover this late that nested cannot
work with their setup. It seems a better fit for QEMU to do a sanity
check when applying the nested-hv sPAPR capability and print out an
informative error message.

sPAPR capabilities are checked at machine init. If a capability cannot
be used, an error message is printed and QEMU exits. In most places,
the error message also contains an hint for the user. But we should
use error_append_hint() for that, as explained in the "qapi/error.h"
header.

So this series first converts spapr_caps.c to using error_append_hint().
This requires to add some ERRP_GUARD() because spapr_caps_apply() passes
&error_fatal. Then it adds a sanity check for the nested-hv case with
an error message and hint.

v4: - Same as v3 but rebased on ppc-for-5.2, updated changelogs
      and cover
v3: - Add preliminary patch to use warn_report() instead of
      a convoluted error_setg()+warn_report_err() sequence
v2: - Fix indentation and add some missing \n in patch 2
    - Add ERRP_AUTO_PROPAGATE() to cap_nested_kvm_hv_apply() in
      patch 2 instead of patch 3

---

Greg Kurz (2):
      spapr: Use error_append_hint() in spapr_caps.c
      spapr: Forbid nested KVM-HV in pre-power9 compat mode


 hw/ppc/spapr_caps.c |   99 +++++++++++++++++++++++++++++++--------------------
 1 file changed, 60 insertions(+), 39 deletions(-)

--
Greg