[PATCH REBASED v5 2/2] spapr: nvdimm: Introduce spapr-nvdimm device

[Shivaprasad G Bhat <sbhat@xxxxxxxxxxxxx>]

If the device backend is not persistent memory for the nvdimm, there is
need for explicit IO flushes on the backend to ensure persistence.

On SPAPR, the issue is addressed by adding a new hcall to request for
an explicit flush from the guest when the backend is not pmem. So, the
approach here is to convey when the hcall flush is required in a device
tree property. The guest once it knows the device backend is not pmem,
makes the hcall whenever flush is required.

To set the device tree property, the patch introduces a new papr specific
device type inheriting the nvdimm device. When the backend doesn't have
pmem="yes", the device tree property "ibm,hcall-flush-required" is set,
and the guest makes hcall H_SCM_FLUSH requesting for an explicit flush.

Signed-off-by: Shivaprasad G Bhat <sbhat@xxxxxxxxxxxxx>
---
 hw/ppc/spapr_nvdimm.c         |   46 +++++++++++++++++++++++++++++++++++++++++
 include/hw/ppc/spapr_nvdimm.h |    4 ++++
 2 files changed, 50 insertions(+)

diff --git a/hw/ppc/spapr_nvdimm.c b/hw/ppc/spapr_nvdimm.c
index 4f8931ab15..4dc7c3f147 100644
--- a/hw/ppc/spapr_nvdimm.c
+++ b/hw/ppc/spapr_nvdimm.c
@@ -54,6 +54,8 @@ bool spapr_nvdimm_validate(HotplugHandler *hotplug_dev, NVDIMMDevice *nvdimm,
 {
     const MachineClass *mc = MACHINE_GET_CLASS(hotplug_dev);
     const MachineState *ms = MACHINE(hotplug_dev);
+    PCDIMMDevice *dimm = PC_DIMM(nvdimm);
+    MemoryRegion *mr = host_memory_backend_get_memory(dimm->hostmem);
     g_autofree char *uuidstr = NULL;
     QemuUUID uuid;
     int ret;
@@ -91,6 +93,14 @@ bool spapr_nvdimm_validate(HotplugHandler *hotplug_dev, NVDIMMDevice *nvdimm,
         return false;
     }
 
+    if (object_dynamic_cast(OBJECT(nvdimm), TYPE_SPAPR_NVDIMM) &&
+        (memory_region_get_fd(mr) < 0)) {
+        error_setg(errp, "spapr-nvdimm device requires the "
+                   "memdev %s to be of memory-backend-file type",
+                   object_get_canonical_path_component(OBJECT(dimm->hostmem)));
+        return false;
+    }
+
     return true;
 }
 
@@ -162,6 +172,21 @@ static int spapr_dt_nvdimm(SpaprMachineState *spapr, void *fdt,
                              "operating-system")));
     _FDT(fdt_setprop(fdt, child_offset, "ibm,cache-flush-required", NULL, 0));
 
+    if (object_dynamic_cast(OBJECT(nvdimm), TYPE_SPAPR_NVDIMM)) {
+        bool is_pmem = false;
+#ifdef CONFIG_LIBPMEM
+        PCDIMMDevice *dimm = PC_DIMM(nvdimm);
+        HostMemoryBackend *hostmem = dimm->hostmem;
+
+        is_pmem = object_property_get_bool(OBJECT(hostmem), "pmem",
+                                           &error_abort);
+#endif
+        if (!is_pmem) {
+            _FDT(fdt_setprop(fdt, child_offset, "ibm,hcall-flush-required",
+                             NULL, 0));
+        }
+    }
+
     return child_offset;
 }
 
@@ -585,7 +610,16 @@ static target_ulong h_scm_flush(PowerPCCPU *cpu, SpaprMachineState *spapr,
     }
 
     dimm = PC_DIMM(drc->dev);
+    if (!object_dynamic_cast(OBJECT(dimm), TYPE_SPAPR_NVDIMM)) {
+        return H_PARAMETER;
+    }
+
     backend = MEMORY_BACKEND(dimm->hostmem);
+#ifdef CONFIG_LIBPMEM
+    if (object_property_get_bool(OBJECT(backend), "pmem", &error_abort)) {
+        return H_UNSUPPORTED;
+    }
+#endif
     fd = memory_region_get_fd(&backend->mr);
 
     if (fd < 0) {
@@ -766,3 +800,15 @@ static void spapr_scm_register_types(void)
 }
 
 type_init(spapr_scm_register_types)
+
+static TypeInfo spapr_nvdimm_info = {
+    .name          = TYPE_SPAPR_NVDIMM,
+    .parent        = TYPE_NVDIMM,
+};
+
+static void spapr_nvdimm_register_types(void)
+{
+    type_register_static(&spapr_nvdimm_info);
+}
+
+type_init(spapr_nvdimm_register_types)
diff --git a/include/hw/ppc/spapr_nvdimm.h b/include/hw/ppc/spapr_nvdimm.h
index 24d8e37b33..fb4e56418e 100644
--- a/include/hw/ppc/spapr_nvdimm.h
+++ b/include/hw/ppc/spapr_nvdimm.h
@@ -13,6 +13,10 @@
 #include "hw/mem/nvdimm.h"
 #include "migration/vmstate.h"
 
+#define TYPE_SPAPR_NVDIMM "spapr-nvdimm"
+OBJECT_DECLARE_SIMPLE_TYPE(SpaprNVDIMMDevice, SPAPR_NVDIMM)
+
+typedef struct SpaprNVDIMMDevice  SpaprNVDIMMDevice;
 typedef struct SpaprDrc SpaprDrc;
 typedef struct SpaprMachineState SpaprMachineState;