On Hypervisor.framework for macOS and WHPX for Windows, the provided environment is a GICv3 without ITS.

As such, support a GICv3 w/ GICv2m for that scenario.

Signed-off-by: Mohamed Mediouni <mohamed@unpredictable.fr>

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
---
 hw/arm/virt-acpi-build.c | 4 +++-
 hw/arm/virt.c            | 8 ++++++++
 include/hw/arm/virt.h    | 2 ++
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
index 96830f7c4e..7a049b8328 100644
--- a/hw/arm/virt-acpi-build.c
+++ b/hw/arm/virt-acpi-build.c
@@ -959,7 +959,9 @@ build_madt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
             build_append_int_noprefix(table_data, memmap[VIRT_GIC_ITS].base, 8);
             build_append_int_noprefix(table_data, 0, 4);    /* Reserved */
         }
-    } else {
+    }
+
+    if (!vms->its && !vms->no_gicv3_with_gicv2m) {
         const uint16_t spi_base = vms->irqmap[VIRT_GIC_V2M] + ARM_SPI_BASE;
 
         /* 5.2.12.16 GIC MSI Frame Structure */
diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index 02209fadcf..01274ec804 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -956,6 +956,8 @@ static void create_gic(VirtMachineState *vms, MemoryRegion *mem)
 
     if (vms->gic_version != VIRT_GIC_VERSION_2 && vms->its) {
         create_its(vms);
+    } else if (vms->gic_version != VIRT_GIC_VERSION_2 && !vms->no_gicv3_with_gicv2m) {
+        create_v2m(vms);
     } else if (vms->gic_version == VIRT_GIC_VERSION_2) {
         create_v2m(vms);
     }
@@ -2433,6 +2435,8 @@ static void machvirt_init(MachineState *machine)
     vms->ns_el2_virt_timer_irq = ns_el2_virt_timer_present() &&
         !vmc->no_ns_el2_virt_timer_irq;
 
+    vms->no_gicv3_with_gicv2m = vmc->no_gicv3_with_gicv2m;
+
     fdt_add_timer_nodes(vms);
     fdt_add_cpu_nodes(vms);
 
@@ -3467,6 +3471,7 @@ static void virt_instance_init(Object *obj)
     vms->its = true;
     /* Allow ITS emulation if the machine version supports it */
     vms->tcg_its = !vmc->no_tcg_its;
+    vms->no_gicv3_with_gicv2m = false;
 
     /* Default disallows iommu instantiation */
     vms->iommu = VIRT_IOMMU_NONE;
@@ -3519,8 +3524,11 @@ DEFINE_VIRT_MACHINE_AS_LATEST(10, 2)
 
 static void virt_machine_10_1_options(MachineClass *mc)
 {
+    VirtMachineClass *vmc = VIRT_MACHINE_CLASS(OBJECT_CLASS(mc));
+
     virt_machine_10_2_options(mc);
     compat_props_add(mc->compat_props, hw_compat_10_1, hw_compat_10_1_len);
+    vmc->no_gicv3_with_gicv2m = true;
 }
 DEFINE_VIRT_MACHINE(10, 1)
 
diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
index ea2cff05b0..3c030f4b5d 100644
--- a/include/hw/arm/virt.h
+++ b/include/hw/arm/virt.h
@@ -131,6 +131,7 @@ struct VirtMachineClass {
     bool no_cpu_topology;
     bool no_tcg_lpa2;
     bool no_ns_el2_virt_timer_irq;
+    bool no_gicv3_with_gicv2m;
     bool no_nested_smmu;
 };
 
@@ -178,6 +179,7 @@ struct VirtMachineState {
     char *oem_id;
     char *oem_table_id;
     bool ns_el2_virt_timer_irq;
+    bool no_gicv3_with_gicv2m;
     CXLState cxl_devices_state;
     bool legacy_smmuv3_present;
 };
-- 
2.50.1 (Apple Git-155)

On Sat, 20 Sept 2025 at 15:02, Mohamed Mediouni
<mohamed@unpredictable.fr> wrote:
>
> On Hypervisor.framework for macOS and WHPX for Windows, the provided environment is a GICv3 without ITS.
>
> As such, support a GICv3 w/ GICv2m for that scenario.
>
> Signed-off-by: Mohamed Mediouni <mohamed@unpredictable.fr>
>
> Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
> ---
>  hw/arm/virt-acpi-build.c | 4 +++-
>  hw/arm/virt.c            | 8 ++++++++
>  include/hw/arm/virt.h    | 2 ++
>  3 files changed, 13 insertions(+), 1 deletion(-)

Looking at this I find myself wondering whether we need the
old-version back compat handling. The cases I think we have
at the moment are:

 (1) TCG, virt-6.1 and earlier: no_tcg_its is set
   -- you can have a gicv2 (always with a gicv2m)
   -- if you specify gic-version=3 you get a GICv3 without ITS
 (2) TCG, virt-6.2 and later:
   -- gic-version=2 still has gicv2m
   -- gic-version=3 by default gives you an ITS; if you also
      say its=off you get GICv3 with no ITS
   -- there is no case where we provide a GICv3 and are
      unable to provide an ITS for it
 (3) KVM (any version):
   -- gic-version=2 has a gicv2m
   -- gic-version=3 gives you an ITS by default; its=off
      will remove it
   -- there is no case where we provide a GICv3 and are
      unable to provide an ITS for it
 (4) HVF:
   -- only gic-version=2 works, you get a gicv2m

and I think what we want is:
 (a) if you explicitly disable the ITS (with its=off or via
     no_tcg_its) you get no ITS (and no gicv2m)
 (b) if you explicitly enable the ITS you should get an
     actual ITS or an error message
 (c) the default should be its=auto which gives
     you "ITS if we can, gicv2m if we can't".
     This is repurposing the its= property as "message signaled
     interrupt support", which is a little bit of a hack
     but I think OK if we're clear about it in the docs.
     (We could rename the property to "msi=(off,its,gicv2m,auto)"
     with back-compat support for "its=" but I don't know if
     that's worth the effort.)

And then that doesn't need any back-compat handling for pre-10.2
machine types or a "no_gicv3_with_gicv2m" flag, because for
10.1 and earlier there is no case that currently works and
which falls into category (c) and which doesn't give you an ITS.
(because we don't yet have hvf gicv3 implemented: that's a new
feature that never worked in 10.1.)

What do you think?

thanks
-- PMM