Commit ee4d1ff3af for qemu.org
commit ee4d1ff3af85418a1dd946647658b954649e43ae
Author: Mohammadfaiz Bawa <mbawa@redhat.com>
Date: Thu Feb 26 11:27:18 2026 +0000
hw/arm/virt: Add virtio-mmio-transports property
Windows ARM64 guests detect virtio-mmio devices declared in ACPI
tables even when no backend is attached. This causes "Unknown
devices" (ACPI\LNRO0005) to appear in Device Manager.
Until Windows fixes that by supporting, add a new machine
property 'virtio-mmio-transports' to control the number of
virtio-mmio transports instantiated. The default remains
NUM_VIRTIO_TRANSPORTS (32) for backward compatibility.
Setting it to 0 allows users to disable virtio-mmio entirely.
Usage: -machine virt,virtio-mmio-transports=0
Signed-off-by: Mohammadfaiz Bawa <mbawa@redhat.com>
Message-id: 20260219173256.152743-1-mbawa@redhat.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst
index f8148b5dcf..fbe3ca9e12 100644
--- a/docs/system/arm/virt.rst
+++ b/docs/system/arm/virt.rst
@@ -226,6 +226,11 @@ dtb-randomness
dtb-kaslr-seed
A deprecated synonym for dtb-randomness.
+virtio-mmio-transports
+ Set the number of virtio-mmio transports to create (between 0 and 32;
+ the default is 32). Unused transports are harmless, but you can
+ use this property to avoid exposing them to the guest if you wish.
+
x-oem-id
Set string (up to 6 bytes) to override the default value of field OEMID in ACPI
table header.
diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
index 544004615d..719d2f994e 100644
--- a/hw/arm/virt-acpi-build.c
+++ b/hw/arm/virt-acpi-build.c
@@ -1154,7 +1154,7 @@ build_dsdt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
fw_cfg_acpi_dsdt_add(scope, &memmap[VIRT_FW_CFG]);
virtio_acpi_dsdt_add(scope, memmap[VIRT_MMIO].base, memmap[VIRT_MMIO].size,
(irqmap[VIRT_MMIO] + ARM_SPI_BASE),
- 0, NUM_VIRTIO_TRANSPORTS);
+ 0, vms->virtio_transports);
acpi_dsdt_add_pci(scope, memmap, irqmap[VIRT_PCIE] + ARM_SPI_BASE, vms);
if (vms->acpi_dev) {
build_ged_aml(scope, "\\_SB."GED_DEVICE,
diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index 50865e8115..81e700f516 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -1208,7 +1208,7 @@ static void create_virtio_devices(const VirtMachineState *vms)
* between kernel versions). For reliable and stable identification
* of disks users must use UUIDs or similar mechanisms.
*/
- for (i = 0; i < NUM_VIRTIO_TRANSPORTS; i++) {
+ for (i = 0; i < vms->virtio_transports; i++) {
int irq = vms->irqmap[VIRT_MMIO] + i;
hwaddr base = vms->memmap[VIRT_MMIO].base + i * size;
@@ -1223,7 +1223,7 @@ static void create_virtio_devices(const VirtMachineState *vms)
* loop influences virtio device to virtio transport assignment, whereas
* this loop controls how virtio transports are laid out in the dtb.
*/
- for (i = NUM_VIRTIO_TRANSPORTS - 1; i >= 0; i--) {
+ for (i = vms->virtio_transports - 1; i >= 0; i--) {
char *nodename;
int irq = vms->irqmap[VIRT_MMIO] + i;
hwaddr base = vms->memmap[VIRT_MMIO].base + i * size;
@@ -2826,6 +2826,36 @@ static void virt_set_its(Object *obj, bool value, Error **errp)
}
}
+static void virt_get_virtio_transports(Object *obj, Visitor *v,
+ const char *name, void *opaque,
+ Error **errp)
+{
+ VirtMachineState *vms = VIRT_MACHINE(obj);
+ uint8_t transports = vms->virtio_transports;
+
+ visit_type_uint8(v, name, &transports, errp);
+}
+
+static void virt_set_virtio_transports(Object *obj, Visitor *v,
+ const char *name, void *opaque,
+ Error **errp)
+{
+ VirtMachineState *vms = VIRT_MACHINE(obj);
+ uint8_t transports;
+
+ if (!visit_type_uint8(v, name, &transports, errp)) {
+ return;
+ }
+
+ if (transports > NUM_VIRTIO_TRANSPORTS) {
+ error_setg(errp, "virtio-mmio-transports must not exceed %d",
+ NUM_VIRTIO_TRANSPORTS);
+ return;
+ }
+
+ vms->virtio_transports = transports;
+}
+
static bool virt_get_dtb_randomness(Object *obj, Error **errp)
{
VirtMachineState *vms = VIRT_MACHINE(obj);
@@ -3535,6 +3565,13 @@ static void virt_machine_class_init(ObjectClass *oc, const void *data)
"Set the high memory region size "
"for PCI MMIO");
+ object_class_property_add(oc, "virtio-mmio-transports", "uint8",
+ virt_get_virtio_transports,
+ virt_set_virtio_transports,
+ NULL, NULL);
+ object_class_property_set_description(oc, "virtio-mmio-transports",
+ "Set the number of virtio-mmio transports to instantiate");
+
object_class_property_add_str(oc, "gic-version", virt_get_gic_version,
virt_set_gic_version);
object_class_property_set_description(oc, "gic-version",
@@ -3654,6 +3691,8 @@ static void virt_instance_init(Object *obj)
vms->irqmap = a15irqmap;
+ vms->virtio_transports = NUM_VIRTIO_TRANSPORTS;
+
virt_flash_create(vms);
vms->oem_id = g_strndup(ACPI_BUILD_APPNAME6, 6);
diff --git a/include/hw/arm/virt.h b/include/hw/arm/virt.h
index 8069422769..dba8ac7f2f 100644
--- a/include/hw/arm/virt.h
+++ b/include/hw/arm/virt.h
@@ -172,6 +172,7 @@ struct VirtMachineState {
uint32_t msi_phandle;
uint32_t iommu_phandle;
int psci_conduit;
+ uint8_t virtio_transports;
hwaddr highest_gpa;
DeviceState *gic;
DeviceState *acpi_dev;