[PATCH RFCv3 7/9] s390x: prepare device memory address space

[David Hildenbrand]

Let's allocate the device memory information and setup the device
memory address space. The RAM size returned via SCLP is not modified. Guest
OSs which support memory devices (like virtio-mem) are expected to
consult diag500(4).

Signed-off-by: David Hildenbrand <david@redhat.com>
---
 hw/s390x/s390-virtio-ccw.c         | 37 ++++++++++++++++++++++++++++++
 hw/s390x/sclp.c                    |  6 ++++-
 include/hw/s390x/s390-virtio-ccw.h |  3 +++
 3 files changed, 45 insertions(+), 1 deletion(-)

diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
index b481e5e5bd..23b94256e0 100644
--- a/hw/s390x/s390-virtio-ccw.c
+++ b/hw/s390x/s390-virtio-ccw.c
@@ -115,6 +115,29 @@ static void subsystem_reset(void)
     }
 }
 
+static void s390_device_memory_init(MachineState *machine)
+{
+    MemoryRegion *sysmem = get_system_memory();
+
+    machine->device_memory = g_malloc0(sizeof(*machine->device_memory));
+
+    /* initialize device memory address space */
+    if (machine->ram_size < machine->maxram_size) {
+        ram_addr_t device_mem_size = machine->maxram_size - machine->ram_size;
+
+        if (!QEMU_IS_ALIGNED(machine->maxram_size, MiB)) {
+            error_report("maximum memory size must be aligned to 1 MB");
+            exit(EXIT_FAILURE);
+        }
+
+        machine->device_memory->base = machine->ram_size;
+        memory_region_init(&machine->device_memory->mr, OBJECT(machine),
+                           "device-memory", device_mem_size);
+        memory_region_add_subregion(sysmem, machine->device_memory->base,
+                                    &machine->device_memory->mr);
+    }
+}
+
 static void s390_memory_init(MachineState *machine)
 {
     MemoryRegion *sysmem = get_system_memory();
@@ -149,6 +172,11 @@ static void s390_memory_init(MachineState *machine)
     s390_skeys_init();
     /* Initialize storage attributes device */
     s390_stattrib_init();
+
+    /* Support for memory devices is glued to compat machines. */
+    if (memory_devices_allowed()) {
+        s390_device_memory_init(machine);
+    }
 }
 
 static void s390_init_ipl_dev(const char *kernel_filename,
@@ -569,6 +597,7 @@ static void ccw_machine_class_init(ObjectClass *oc, void 
*data)
     s390mc->cpu_model_allowed = true;
     s390mc->css_migration_enabled = true;
     s390mc->hpage_1m_allowed = true;
+    s390mc->memory_devices_allowed = true;
     mc->init = ccw_init;
     mc->reset = s390_machine_reset;
     mc->hot_add_cpu = s390_hot_add_cpu;
@@ -665,6 +694,11 @@ bool hpage_1m_allowed(void)
     return get_machine_class()->hpage_1m_allowed;
 }
 
+bool memory_devices_allowed(void)
+{
+    return get_machine_class()->memory_devices_allowed;
+}
+
 static char *machine_get_loadparm(Object *obj, Error **errp)
 {
     S390CcwMachineState *ms = S390_CCW_MACHINE(obj);
@@ -783,8 +817,11 @@ static void ccw_machine_5_0_instance_options(MachineState 
*machine)
 
 static void ccw_machine_5_0_class_options(MachineClass *mc)
 {
+    S390CcwMachineClass *s390mc = S390_MACHINE_CLASS(mc);
+
     ccw_machine_5_1_class_options(mc);
     compat_props_add(mc->compat_props, hw_compat_5_0, hw_compat_5_0_len);
+    s390mc->memory_devices_allowed = false;
 }
 DEFINE_CCW_MACHINE(5_0, "5.0", false);
 
diff --git a/hw/s390x/sclp.c b/hw/s390x/sclp.c
index f59195e15a..316ff9c218 100644
--- a/hw/s390x/sclp.c
+++ b/hw/s390x/sclp.c
@@ -22,6 +22,7 @@
 #include "hw/s390x/event-facility.h"
 #include "hw/s390x/s390-pci-bus.h"
 #include "hw/s390x/ipl.h"
+#include "hw/s390x/s390-virtio-ccw.h"
 
 static inline SCLPDevice *get_sclp_device(void)
 {
@@ -110,7 +111,10 @@ static void read_SCP_info(SCLPDevice *sclp, SCCB *sccb)
         read_info->rnsize2 = cpu_to_be32(rnsize);
     }
 
-    /* we don't support standby memory, maxram_size is never exposed */
+    /*
+     * We don't support standby memory. Currently, maxram_size is only
+     * implicitly exposed via diag500(4) to indicate the device memory region.
+     */
     rnmax = machine->ram_size >> sclp->increment_size;
     if (rnmax < 0x10000) {
         read_info->rnmax = cpu_to_be16(rnmax);
diff --git a/include/hw/s390x/s390-virtio-ccw.h 
b/include/hw/s390x/s390-virtio-ccw.h
index cd1dccc6e3..960eb9344f 100644
--- a/include/hw/s390x/s390-virtio-ccw.h
+++ b/include/hw/s390x/s390-virtio-ccw.h
@@ -41,6 +41,7 @@ typedef struct S390CcwMachineClass {
     bool cpu_model_allowed;
     bool css_migration_enabled;
     bool hpage_1m_allowed;
+    bool memory_devices_allowed;
 } S390CcwMachineClass;
 
 /* runtime-instrumentation allowed by the machine */
@@ -49,6 +50,8 @@ bool ri_allowed(void);
 bool cpu_model_allowed(void);
 /* 1M huge page mappings allowed by the machine */
 bool hpage_1m_allowed(void);
+/* memory devices are allowed by the machine (device memory region created). */
+bool memory_devices_allowed(void);
 
 /**
  * Returns true if (vmstate based) migration of the channel subsystem
-- 
2.26.2