[Qemu-devel] [PATCH 08/11] pc: align DIMM's address/size by backend's alignment value

[Igor Mammedov <imammedo@redhat.com>]

Performance wise it's better to align GVA by the backend's
page size.

Also do not allow to create DIMM device with suboptimal
size (i.e. not aligned to backends page size) to aviod
memory loss.

Do above only for 2.2 and newer machine types to avoid
breaking working configs with 2.1 machine type.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
---
 hw/i386/pc.c         | 15 +++++++++++++++
 hw/i386/pc_piix.c    |  3 +++
 hw/i386/pc_q35.c     |  3 +++
 include/hw/i386/pc.h |  4 ++++
 4 files changed, 25 insertions(+)

diff --git a/hw/i386/pc.c b/hw/i386/pc.c
index 1460074..ed50344 100644
--- a/hw/i386/pc.c
+++ b/hw/i386/pc.c
@@ -1605,6 +1605,10 @@ static void pc_dimm_plug(HotplugHandler *hotplug_dev,
         goto out;
     }
 
+    if (memory_region_get_alignment(mr) && pcms->enforce_aligned_dimm) {
+        align = memory_region_get_alignment(mr);
+    }
+
     addr = pc_dimm_get_free_addr(pcms->hotplug_memory_base,
                                  memory_region_size(&pcms->hotplug_memory),
                                  !addr ? NULL : &addr, align,
@@ -1727,6 +1731,13 @@ static void pc_machine_set_max_ram_below_4g(Object *obj, Visitor *v,
     pcms->max_ram_below_4g = value;
 }
 
+static bool pc_machine_get_aligned_dimm(Object *obj, Error **errp)
+{
+    PCMachineState *pcms = PC_MACHINE(obj);
+
+    return pcms->enforce_aligned_dimm;
+}
+
 static void pc_machine_initfn(Object *obj)
 {
     PCMachineState *pcms = PC_MACHINE(obj);
@@ -1739,6 +1750,10 @@ static void pc_machine_initfn(Object *obj)
                         pc_machine_get_max_ram_below_4g,
                         pc_machine_set_max_ram_below_4g,
                         NULL, NULL, NULL);
+    pcms->enforce_aligned_dimm = true;
+    object_property_add_bool(obj, PC_MACHINE_ENFORCE_ALINED_DIMM,
+                             pc_machine_get_aligned_dimm,
+                             NULL, NULL);
 }
 
 static void pc_machine_class_init(ObjectClass *oc, void *data)
diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index 162b77e..4adcd9b 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -304,6 +304,9 @@ static void pc_init_pci(MachineState *machine)
 
 static void pc_compat_2_1(MachineState *machine)
 {
+    PCMachineState *pcms = PC_MACHINE(machine);
+
+    pcms->enforce_aligned_dimm = false;
 }
 
 static void pc_compat_2_0(MachineState *machine)
diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index 0490980..cf4953e 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -282,6 +282,9 @@ static void pc_q35_init(MachineState *machine)
 
 static void pc_compat_2_1(MachineState *machine)
 {
+    PCMachineState *pcms = PC_MACHINE(machine);
+
+    pcms->enforce_aligned_dimm = false;
 }
 
 static void pc_compat_2_0(MachineState *machine)
diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
index c4ee520..a4e2a39 100644
--- a/include/hw/i386/pc.h
+++ b/include/hw/i386/pc.h
@@ -23,6 +23,8 @@
  * address space begins.
  * @hotplug_memory: hotplug memory addess space container
  * @acpi_dev: link to ACPI PM device that performs ACPI hotplug handling
+ * @enforce_aligned_dimm: check that DIMM's address/size is aligned by
+ *                        backend's alignment value if provided
  */
 struct PCMachineState {
     /*< private >*/
@@ -35,11 +37,13 @@ struct PCMachineState {
     HotplugHandler *acpi_dev;
 
     uint64_t max_ram_below_4g;
+    bool enforce_aligned_dimm;
 };
 
 #define PC_MACHINE_ACPI_DEVICE_PROP "acpi-device"
 #define PC_MACHINE_MEMHP_REGION_SIZE "hotplug-memory-region-size"
 #define PC_MACHINE_MAX_RAM_BELOW_4G "max-ram-below-4g"
+#define PC_MACHINE_ENFORCE_ALINED_DIMM "enforce-aligned-dimm"
 
 /**
  * PCMachineClass:
-- 
1.8.3.1