ppc/spapr_nvdimm: do not enable support with 'nvdimm=off'

The NVDIMM support for pSeries was introduced in 5.1, but it
didn't contemplate the 'nvdimm' machine option that other
archs uses. For every other arch, if no '-machine nvdimm(=on)'
is present, it is assumed that the NVDIMM support is disabled.
The user must explictly inform that the machine supports
NVDIMM. For pseries-5.1 the 'nvdimm' option is completely
ignored, and support is always assumed to exist. This
leads to situations where the user is able to set 'nvdimm=off'
but the guest boots up with the NVDIMMs anyway.

Fixing this now, after 5.1 launch, can put the overall NVDIMM
support for pseries in a strange place regarding this 'nvdimm'
machine option. If we force everything to be like other archs,
existing pseries-5.1 guests that didn't use 'nvdimm' to use NVDIMM
devices will break. If we attempt to make the newer pseries
machines (5.2+) behave like everyone else, but keep pseries-5.1
untouched, we'll have consistency problems on machine upgrade
(5.1 will have different default values for NVDIMM support than
5.2).

The common ground here is, if the user sets 'nvdimm=off', we
must comply regardless of being 5.1 or 5.2+. This patch
changes spapr_nvdimm_validate() to verify if the user set
NVDIMM support off in the machine options and, in that
case, error out if we have a NVDIMM device. The default
value for 5.2+ pseries machines will still be 'nvdimm=on'
when there is no 'nvdimm' option declared, just like it is today
with pseries-5.1. In the end we'll have different default
semantics from everyone else in the absence of the 'nvdimm'
machine option, but this boat has sailed.

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1848887
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20200825215749.213536-4-danielhb413@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

0 files changed, 0 insertions, 0 deletions