[PATCH 3/3] ppc/spapr_nvdimm: do not enable support with 'nvdimm=off'

[Daniel Henrique Barboza <danielhb413@gmail.com>]

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>
---
 hw/ppc/spapr_nvdimm.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/hw/ppc/spapr_nvdimm.c b/hw/ppc/spapr_nvdimm.c
index bc2b65420c..95cbc30528 100644
--- a/hw/ppc/spapr_nvdimm.c
+++ b/hw/ppc/spapr_nvdimm.c
@@ -27,13 +27,17 @@
 #include "hw/ppc/spapr_nvdimm.h"
 #include "hw/mem/nvdimm.h"
 #include "qemu/nvdimm-utils.h"
+#include "qemu/option.h"
 #include "hw/ppc/fdt.h"
 #include "qemu/range.h"
+#include "sysemu/sysemu.h"
 
 void spapr_nvdimm_validate(HotplugHandler *hotplug_dev, NVDIMMDevice *nvdimm,
                            uint64_t size, Error **errp)
 {
     const MachineClass *mc = MACHINE_GET_CLASS(hotplug_dev);
+    const MachineState *ms = MACHINE(hotplug_dev);
+    const char *nvdimm_opt = qemu_opt_get(qemu_get_machine_opts(), "nvdimm");
     g_autofree char *uuidstr = NULL;
     QemuUUID uuid;
     int ret;
@@ -43,6 +47,20 @@ void spapr_nvdimm_validate(HotplugHandler *hotplug_dev, NVDIMMDevice *nvdimm,
         return;
     }
 
+    /*
+     * NVDIMM support went live in 5.1 without considering that, in
+     * other archs, the user needs to enable NVDIMM support with the
+     * 'nvdimm' machine option and the default behavior is NVDIMM
+     * support disabled. It is too late to roll back to the standard
+     * behavior without breaking 5.1 guests. What we can do is to
+     * ensure that, if the user sets nvdimm=off, we error out
+     * regardless of being 5.1 or newer.
+     */
+    if (!ms->nvdimms_state->is_enabled && nvdimm_opt) {
+        error_setg(errp, "nvdimm device found but 'nvdimm=off' was set");
+        return;
+    }
+
     if (object_property_get_int(OBJECT(nvdimm), NVDIMM_LABEL_SIZE_PROP,
                                 &error_abort) == 0) {
         error_setg(errp, "PAPR requires NVDIMM devices to have label-size set");
-- 
2.26.2