[PATCH v7 15/24] hw/arm: virt: cleanly fail on attempt to use the platform vGIC together with ITS

Mohamed Mediouni
2025-10-16T16:57:21Z

Switch its to a tristate.

Windows Hypervisor Platform's vGIC doesn't support ITS.
Deal with this by reporting to the user and exiting.

Regular configuration: GICv3 + ITS
New default configuration with WHPX: GICv3 with GICv2m
And its=off explicitly for the newest machine version: GICv3 + GICv2m

Signed-off-by: Mohamed Mediouni <mohamed@unpredictable.fr>
---
hw/arm/virt-acpi-build.c | 14 +++++------
hw/arm/virt.c | 50 ++++++++++++++++++++++++++++++++--------
include/hw/arm/virt.h | 4 +++-
3 files changed, 50 insertions(+), 18 deletions(-)

diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
index 0a6ec74aa0..c716130206 100644
--- a/hw/arm/virt-acpi-build.c
+++ b/hw/arm/virt-acpi-build.c
@@ -472,7 +472,7 @@ build_iort(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
nb_nodes = num_smmus + 1; /* RC and SMMUv3 */
rc_mapping_count = rc_smmu_idmaps_len;

- if (vms->its) {
+ if (virt_is_its_enabled(vms)) {
/*
* Knowing the ID ranges from the RC to the SMMU, it's possible to
* determine the ID ranges from RC that go directly to ITS.
@@ -483,7 +483,7 @@ build_iort(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
rc_mapping_count += rc_its_idmaps->len;
}
} else {
- if (vms->its) {
+ if (virt_is_its_enabled(vms)) {
nb_nodes = 2; /* RC and ITS */
rc_mapping_count = 1; /* Direct map to ITS */
} else {
@@ -498,7 +498,7 @@ build_iort(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
build_append_int_noprefix(table_data, IORT_NODE_OFFSET, 4);
build_append_int_noprefix(table_data, 0, 4); /* Reserved */

- if (vms->its) {
+ if (virt_is_its_enabled(vms)) {
/* Table 12 ITS Group Format */
build_append_int_noprefix(table_data, 0 /* ITS Group */, 1); /* Type */
node_size = 20 /* fixed header size */ + 4 /* 1 GIC ITS Identifier */;
@@ -517,7 +517,7 @@ build_iort(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
int smmu_mapping_count, offset_to_id_array;
int irq = sdev->irq;

- if (vms->its) {
+ if (virt_is_its_enabled(vms)) {
smmu_mapping_count = 1; /* ITS Group node */
offset_to_id_array = SMMU_V3_ENTRY_SIZE; /* Just after the header */
} else {
@@ -610,7 +610,7 @@ build_iort(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
}
}

- if (vms->its) {
+ if (virt_is_its_enabled(vms)) {
/*
* Map bypassed (don't go through the SMMU) RIDs (input) to
* ITS Group node directly: RC -> ITS.
@@ -945,7 +945,7 @@ build_madt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
memmap[VIRT_HIGH_GIC_REDIST2].size);
}

- if (vms->its) {
+ if (virt_is_its_enabled(vms)) {
/*
* ACPI spec, Revision 6.0 Errata A
* (original 6.0 definition has invalid Length)
@@ -961,7 +961,7 @@ build_madt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
}
}

- if (!(vms->gic_version != VIRT_GIC_VERSION_2 && vms->its) && !vms->no_gicv3_with_gicv2m) {
+ if (virt_is_its_enabled(vms) && !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 9121eb37eb..1bebbc265d 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -735,7 +735,7 @@ static void create_its(VirtMachineState *vms)
{
DeviceState *dev;

- assert(vms->its);
+ assert(virt_is_its_enabled(vms));
if (!kvm_irqchip_in_kernel() && !vms->tcg_its) {
/*
* Do nothing if ITS is neither supported by the host nor emulated by
@@ -744,6 +744,15 @@ static void create_its(VirtMachineState *vms)
return;
}

+ if (whpx_enabled() && vms->tcg_its) {
+ /*
+ * Signal to the user when ITS is neither supported by the host
+ * nor emulated by the machine.
+ */
+ info_report("ITS not supported on WHPX.");
+ exit(1);
+ }
+
dev = qdev_new(its_class_name());

object_property_set_link(OBJECT(dev), "parent-gicv3", OBJECT(vms->gic),
@@ -955,7 +964,7 @@ static void create_gic(VirtMachineState *vms, MemoryRegion *mem)

fdt_add_gic_node(vms);

- if (vms->gic_version != VIRT_GIC_VERSION_2 && vms->its) {
+ if (vms->gic_version != VIRT_GIC_VERSION_2 && virt_is_its_enabled(vms)) {
create_its(vms);
} else if (vms->gic_version != VIRT_GIC_VERSION_2 && !vms->no_gicv3_with_gicv2m) {
create_v2m(vms);
@@ -2705,18 +2714,38 @@ static void virt_set_highmem_mmio_size(Object *obj, Visitor *v,
extended_memmap[VIRT_HIGH_PCIE_MMIO].size = size;
}

-static bool virt_get_its(Object *obj, Error **errp)
+bool virt_is_its_enabled(VirtMachineState *vms)
+{
+ if (vms->gic_version == VIRT_GIC_VERSION_2) {
+ return false;
+ }
+
+ if (vms->its == ON_OFF_AUTO_OFF) {
+ return false;
+ }
+ if (vms->its == ON_OFF_AUTO_AUTO) {
+ if (whpx_enabled()) {
+ return false;
+ }
+ }
+ return true;
+}
+
+static void virt_get_its(Object *obj, Visitor *v, const char *name,
+ void *opaque, Error **errp)
{
VirtMachineState *vms = VIRT_MACHINE(obj);
+ OnOffAuto its = vms->its;

- return vms->its;
+ visit_type_OnOffAuto(v, name, &its, errp);
}

-static void virt_set_its(Object *obj, bool value, Error **errp)
+static void virt_set_its(Object *obj, Visitor *v, const char *name,
+ void *opaque, Error **errp)
{
VirtMachineState *vms = VIRT_MACHINE(obj);

- vms->its = value;
+ visit_type_OnOffAuto(v, name, &vms->its, errp);
}

static bool virt_get_dtb_randomness(Object *obj, Error **errp)
@@ -3426,8 +3455,9 @@ static void virt_machine_class_init(ObjectClass *oc, const void *data)
"guest CPU which implements the ARM "
"Memory Tagging Extension");

- object_class_property_add_bool(oc, "its", virt_get_its,
- virt_set_its);
+ object_class_property_add(oc, "its", "OnOffAuto",
+ virt_get_its, virt_set_its,
+ NULL, NULL);
object_class_property_set_description(oc, "its",
"Set on/off to enable/disable "
"ITS instantiation");
@@ -3487,8 +3517,8 @@ static void virt_instance_init(Object *obj)
vms->highmem_mmio = true;
vms->highmem_redists = true;

- /* Default allows ITS instantiation */
- vms->its = true;
+ /* Default allows ITS instantiation if available */
+ vms->its = ON_OFF_AUTO_AUTO;
/* Allow ITS emulation if the machine version supports it */
vms->tcg_its = !vmc->no_tcg_its;
vms->no_gicv3_with_gicv2m = false;
diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
index d31348dd61..997dd51678 100644
--- a/include/hw/arm/virt.h
+++ b/include/hw/arm/virt.h
@@ -149,7 +149,7 @@ struct VirtMachineState {
bool highmem_ecam;
bool highmem_mmio;
bool highmem_redists;
- bool its;
+ OnOffAuto its;
bool tcg_its;
bool virt;
bool ras;
@@ -218,4 +218,6 @@ static inline int virt_gicv3_redist_region_count(VirtMachineState *vms)
vms->highmem_redists) ? 2 : 1;
}

+bool virt_is_its_enabled(VirtMachineState *vms);
+
#endif /* QEMU_ARM_VIRT_H */
--
2.50.1 (Apple Git-155)