[PATCH v2] hw/arm/virt: Support larger highmem MMIO regions

[Matthew R. Ochs]

The MMIO region size required to support virtualized environments with
large PCI BAR regions can exceed the hardcoded limit configured in QEMU.
For example, a VM with multiple NVIDIA Grace-Hopper GPUs passed through
requires more MMIO memory than the amount provided by VIRT_HIGH_PCIE_MMIO
(currently 512GB). Instead of updating VIRT_HIGH_PCIE_MMIO, introduce a
new parameter, highmem-mmio-size, that specifies the MMIO size required
to support the VM configuration.

Example usage with 1TB MMIO region size:
        -machine virt,gic-version=3,highmem-mmio-size=1T

Signed-off-by: Matthew R. Ochs <mochs@nvidia.com>
---
v2: - Add unit suffix to example in commit message
    - Use existing "high memory region" terminology
    - Resolve minor braces nit

 docs/system/arm/virt.rst |  4 ++++
 hw/arm/virt.c            | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst
index e67e7f0f7c50..f96cf4da2a78 100644
--- a/docs/system/arm/virt.rst
+++ b/docs/system/arm/virt.rst
@@ -138,6 +138,10 @@ highmem-mmio
   Set ``on``/``off`` to enable/disable the high memory region for PCI MMIO.
   The default is ``on``.
 
+highmem-mmio-size
+  Set the high memory region size for PCI MMIO. Must be a power-of-2 and
+  greater than the default size.
+
 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 49eb0355ef0c..d8d62df43f04 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -2773,6 +2773,36 @@ static void virt_set_highmem_mmio(Object *obj, bool 
value, Error **errp)
     vms->highmem_mmio = value;
 }
 
+static void virt_get_highmem_mmio_size(Object *obj, Visitor *v, const char 
*name,
+                          void *opaque, Error **errp)
+{
+    uint64_t size = extended_memmap[VIRT_HIGH_PCIE_MMIO].size;
+
+    visit_type_size(v, name, &size, errp);
+}
+
+static void virt_set_highmem_mmio_size(Object *obj, Visitor *v, const char 
*name,
+                          void *opaque, Error **errp)
+{
+    uint64_t size;
+
+    if (!visit_type_size(v, name, &size, errp)) {
+        return;
+    }
+
+    if (!is_power_of_2(size)) {
+        error_setg(errp, "highmem_mmio_size is not a power-of-2");
+        return;
+    }
+
+    if (size < extended_memmap[VIRT_HIGH_PCIE_MMIO].size) {
+        error_setg(errp, "highmem_mmio_size is less than the default (%lu)",
+                   extended_memmap[VIRT_HIGH_PCIE_MMIO].size);
+        return;
+    }
+
+    extended_memmap[VIRT_HIGH_PCIE_MMIO].size = size;
+}
 
 static bool virt_get_its(Object *obj, Error **errp)
 {
@@ -3446,6 +3476,14 @@ static void virt_machine_class_init(ObjectClass *oc, 
void *data)
                                           "Set on/off to enable/disable high "
                                           "memory region for PCI MMIO");
 
+    object_class_property_add(oc, "highmem-mmio-size", "size",
+                                   virt_get_highmem_mmio_size,
+                                   virt_set_highmem_mmio_size,
+                                   NULL, NULL);
+    object_class_property_set_description(oc, "highmem-mmio-size",
+                                          "Set the high memory region size "
+                                          "for PCI MMIO");
+
     object_class_property_add_str(oc, "gic-version", virt_get_gic_version,
                                   virt_set_gic_version);
     object_class_property_set_description(oc, "gic-version",
-- 
2.46.0