Let's use our new helper and stop always allocating ms->device_memory.
There is no difference in common memory-device code anymore between
ms->device_memory being NULL or the size being 0. So we only have to
teach spapr code that ms->device_memory isn't always around.

We can now modify two maxram_size checks to rely on ms->device_memory
for detecting whether we have memory devices.

Cc: Daniel Henrique Barboza <danielhb413@gmail.com>
Cc: "Cédric Le Goater" <clg@kaod.org>
Cc: David Gibson <david@gibson.dropbear.id.au>
Cc: Greg Kurz <groug@kaod.org>
Cc: Harsh Prateek Bora <harshpb@linux.ibm.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 hw/ppc/spapr.c       | 37 +++++++++++++++++++------------------
 hw/ppc/spapr_hcall.c |  2 +-
 2 files changed, 20 insertions(+), 19 deletions(-)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index dcb7f1c70a..44155f6613 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -546,10 +546,8 @@ static int spapr_dt_dynamic_reconfiguration_memory(SpaprMachineState *spapr,
                                 cpu_to_be32(lmb_size & 0xffffffff)};
     MemoryDeviceInfoList *dimms = NULL;
 
-    /*
-     * Don't create the node if there is no device memory
-     */
-    if (machine->ram_size == machine->maxram_size) {
+    /* Don't create the node if there is no device memory. */
+    if (!machine->device_memory) {
         return 0;
     }
 
@@ -859,16 +857,23 @@ static void spapr_dt_rtas(SpaprMachineState *spapr, void *fdt)
     int rtas;
     GString *hypertas = g_string_sized_new(256);
     GString *qemu_hypertas = g_string_sized_new(256);
-    uint64_t max_device_addr = MACHINE(spapr)->device_memory->base +
-        memory_region_size(&MACHINE(spapr)->device_memory->mr);
     uint32_t lrdr_capacity[] = {
-        cpu_to_be32(max_device_addr >> 32),
-        cpu_to_be32(max_device_addr & 0xffffffff),
+        0,
+        0,
         cpu_to_be32(SPAPR_MEMORY_BLOCK_SIZE >> 32),
         cpu_to_be32(SPAPR_MEMORY_BLOCK_SIZE & 0xffffffff),
         cpu_to_be32(ms->smp.max_cpus / ms->smp.threads),
     };
 
+    /* Do we have device memory? */
+    if (MACHINE(spapr)->device_memory) {
+        uint64_t max_device_addr = MACHINE(spapr)->device_memory->base +
+            memory_region_size(&MACHINE(spapr)->device_memory->mr);
+
+        lrdr_capacity[0] = cpu_to_be32(max_device_addr >> 32);
+        lrdr_capacity[1] = cpu_to_be32(max_device_addr & 0xffffffff);
+    }
+
     _FDT(rtas = fdt_add_subnode(fdt, 0, "rtas"));
 
     /* hypertas */
@@ -2454,6 +2459,7 @@ static void spapr_create_lmb_dr_connectors(SpaprMachineState *spapr)
     uint32_t nr_lmbs = (machine->maxram_size - machine->ram_size)/lmb_size;
     int i;
 
+    g_assert(!nr_lmbs || machine->device_memory);
     for (i = 0; i < nr_lmbs; i++) {
         uint64_t addr;
 
@@ -2866,12 +2872,11 @@ static void spapr_machine_init(MachineState *machine)
     /* map RAM */
     memory_region_add_subregion(sysmem, 0, machine->ram);
 
-    /* always allocate the device memory information */
-    machine->device_memory = g_malloc0(sizeof(*machine->device_memory));
-
     /* initialize hotplug memory address space */
     if (machine->ram_size < machine->maxram_size) {
         ram_addr_t device_mem_size = machine->maxram_size - machine->ram_size;
+        hwaddr device_mem_base;
+
         /*
          * Limit the number of hotpluggable memory slots to half the number
          * slots that KVM supports, leaving the other half for PCI and other
@@ -2890,12 +2895,8 @@ static void spapr_machine_init(MachineState *machine)
             exit(1);
         }
 
-        machine->device_memory->base = ROUND_UP(machine->ram_size,
-                                                SPAPR_DEVICE_MEM_ALIGN);
-        memory_region_init(&machine->device_memory->mr, OBJECT(spapr),
-                           "device-memory", device_mem_size);
-        memory_region_add_subregion(sysmem, machine->device_memory->base,
-                                    &machine->device_memory->mr);
+        device_mem_base = ROUND_UP(machine->ram_size, SPAPR_DEVICE_MEM_ALIGN);
+        memory_devices_init(machine, device_mem_base, device_mem_size);
     }
 
     if (smc->dr_lmb_enabled) {
@@ -5109,7 +5110,7 @@ static bool phb_placement_2_7(SpaprMachineState *spapr, uint32_t index,
     int i;
 
     /* Do we have device memory? */
-    if (MACHINE(spapr)->maxram_size > ram_top) {
+    if (MACHINE(spapr)->device_memory) {
         /* Can't just use maxram_size, because there may be an
          * alignment gap between normal and device memory regions
          */
diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
index b904755575..1dd32f340f 100644
--- a/hw/ppc/spapr_hcall.c
+++ b/hw/ppc/spapr_hcall.c
@@ -31,7 +31,7 @@ bool is_ram_address(SpaprMachineState *spapr, hwaddr addr)
     if (addr < machine->ram_size) {
         return true;
     }
-    if ((addr >= dms->base)
+    if (dms && (addr >= dms->base)
         && ((addr - dms->base) < memory_region_size(&dms->mr))) {
         return true;
     }
-- 
2.40.1

On 30/5/23 13:38, David Hildenbrand wrote:
> Let's use our new helper and stop always allocating ms->device_memory.
> There is no difference in common memory-device code anymore between
> ms->device_memory being NULL or the size being 0. So we only have to
> teach spapr code that ms->device_memory isn't always around.
> 
> We can now modify two maxram_size checks to rely on ms->device_memory
> for detecting whether we have memory devices.
> 
> Cc: Daniel Henrique Barboza <danielhb413@gmail.com>
> Cc: "Cédric Le Goater" <clg@kaod.org>
> Cc: David Gibson <david@gibson.dropbear.id.au>
> Cc: Greg Kurz <groug@kaod.org>
> Cc: Harsh Prateek Bora <harshpb@linux.ibm.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
>   hw/ppc/spapr.c       | 37 +++++++++++++++++++------------------
>   hw/ppc/spapr_hcall.c |  2 +-
>   2 files changed, 20 insertions(+), 19 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>