[PATCH v4 6/6] hw/arm/virt: Add 'compact-highmem' property

[Gavin Shan]

After the improvement to high memory region address assignment is
applied, the memory layout can be changed, introducing possible
migration breakage. For example, VIRT_HIGH_PCIE_MMIO memory region
is disabled or enabled when the optimization is applied or not, with
the following configuration.

  pa_bits              = 40;
  vms->highmem_redists = false;
  vms->highmem_ecam    = false;
  vms->highmem_mmio    = true;

  # qemu-system-aarch64 -accel kvm -cpu host    \
    -machine virt-7.2,compact-highmem={on, off} \
    -m 4G,maxmem=511G -monitor stdio

  Region            compact-highmem=off         compact-highmem=on
  ----------------------------------------------------------------
  RAM               [1GB         512GB]        [1GB         512GB]
  HIGH_GIC_REDISTS  [512GB       512GB+64MB]   [disabled]
  HIGH_PCIE_ECAM    [512GB+256MB 512GB+512MB]  [disabled]
  HIGH_PCIE_MMIO    [disabled]                 [512GB       1TB]

In order to keep backwords compatibility, we need to disable the
optimization on machines, which is virt-7.1 or ealier than it. It
means the optimization is enabled by default from virt-7.2. Besides,
'compact-highmem' property is added so that the optimization can be
explicitly enabled or disabled on all machine types by users.

Signed-off-by: Gavin Shan <gshan@redhat.com>
---
 docs/system/arm/virt.rst |  4 ++++
 hw/arm/virt.c            | 47 ++++++++++++++++++++++++++++++++++++++++
 include/hw/arm/virt.h    |  1 +
 3 files changed, 52 insertions(+)

diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst
index 20442ea2c1..75bf5a4994 100644
--- a/docs/system/arm/virt.rst
+++ b/docs/system/arm/virt.rst
@@ -94,6 +94,10 @@ highmem
   address space above 32 bits. The default is ``on`` for machine types
   later than ``virt-2.12``.
 
+compact-highmem
+  Set ``on``/``off`` to enable/disable compact space for high memory regions.
+  The default is ``on`` for machine types later than ``virt-7.2``
+
 gic-version
   Specify the version of the Generic Interrupt Controller (GIC) to provide.
   Valid values are:
diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index 4164da49e9..9fe65a2ae1 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -174,6 +174,27 @@ static const MemMapEntry base_memmap[] = {
  * Note the extended_memmap is sized so that it eventually also includes the
  * base_memmap entries (VIRT_HIGH_GIC_REDIST2 index is greater than the last
  * index of base_memmap).
+ *
+ * The addresses assigned to these regions are affected by 'compact-highmem'
+ * property, which is to enable or disable the compact space in the Highmem
+ * IO regions. For example, VIRT_HIGH_PCIE_MMIO can be disabled or enabled
+ * depending on the property in the following scenario.
+ *
+ * pa_bits              = 40;
+ * vms->highmem_redists = false;
+ * vms->highmem_ecam    = false;
+ * vms->highmem_mmio    = true;
+ *
+ * # qemu-system-aarch64 -accel kvm -cpu host    \
+ *   -machine virt-7.2,compact-highmem={on, off} \
+ *   -m 4G,maxmem=511G -monitor stdio
+ *
+ * Region            compact-highmem=off        compact-highmem=on
+ * ----------------------------------------------------------------
+ * RAM               [1GB         512GB]        [1GB         512GB]
+ * HIGH_GIC_REDISTS  [512GB       512GB+64MB]   [disabled]
+ * HIGH_PCIE_ECAM    [512GB+256GB 512GB+512MB]  [disabled]
+ * HIGH_PCIE_MMIO    [disabled]                 [512GB       1TB]
  */
 static MemMapEntry extended_memmap[] = {
     /* Additional 64 MB redist region (can contain up to 512 redistributors) */
@@ -2349,6 +2370,20 @@ static void virt_set_highmem(Object *obj, bool value, 
Error **errp)
     vms->highmem = value;
 }
 
+static bool virt_get_compact_highmem(Object *obj, Error **errp)
+{
+    VirtMachineState *vms = VIRT_MACHINE(obj);
+
+    return vms->highmem_compact;
+}
+
+static void virt_set_compact_highmem(Object *obj, bool value, Error **errp)
+{
+    VirtMachineState *vms = VIRT_MACHINE(obj);
+
+    vms->highmem_compact = value;
+}
+
 static bool virt_get_its(Object *obj, Error **errp)
 {
     VirtMachineState *vms = VIRT_MACHINE(obj);
@@ -2967,6 +3002,13 @@ static void virt_machine_class_init(ObjectClass *oc, 
void *data)
                                           "Set on/off to enable/disable using "
                                           "physical address space above 32 
bits");
 
+    object_class_property_add_bool(oc, "compact-highmem",
+                                   virt_get_compact_highmem,
+                                   virt_set_compact_highmem);
+    object_class_property_set_description(oc, "compact-highmem",
+                                          "Set on/off to enable/disable 
compact "
+                                          "space for high memory regions");
+
     object_class_property_add_str(oc, "gic-version", virt_get_gic_version,
                                   virt_set_gic_version);
     object_class_property_set_description(oc, "gic-version",
@@ -3051,6 +3093,7 @@ static void virt_instance_init(Object *obj)
 
     /* High memory is enabled by default */
     vms->highmem = true;
+    vms->highmem_compact = !vmc->no_highmem_compact;
     vms->gic_version = VIRT_GIC_VERSION_NOSEL;
 
     vms->highmem_ecam = !vmc->no_highmem_ecam;
@@ -3120,8 +3163,12 @@ DEFINE_VIRT_MACHINE_AS_LATEST(7, 2)
 
 static void virt_machine_7_1_options(MachineClass *mc)
 {
+    VirtMachineClass *vmc = VIRT_MACHINE_CLASS(OBJECT_CLASS(mc));
+
     virt_machine_7_2_options(mc);
     compat_props_add(mc->compat_props, hw_compat_7_1, hw_compat_7_1_len);
+    /* Compact space for high memory regions was introduced with 7.2 */
+    vmc->no_highmem_compact = true;
 }
 DEFINE_VIRT_MACHINE(7, 1)
 
diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
index 709f623741..c7dd59d7f1 100644
--- a/include/hw/arm/virt.h
+++ b/include/hw/arm/virt.h
@@ -125,6 +125,7 @@ struct VirtMachineClass {
     bool no_pmu;
     bool claim_edge_triggered_timers;
     bool smbios_old_sys_ver;
+    bool no_highmem_compact;
     bool no_highmem_ecam;
     bool no_ged;   /* Machines < 4.2 have no support for ACPI GED device */
     bool kvm_no_adjvtime;
-- 
2.23.0