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
