docs/system/arm/virt.rst | 5 +++++ hw/arm/virt-acpi-build.c | 2 +- hw/arm/virt.c | 43 ++++++++++++++++++++++++++++++++++++++-- include/hw/arm/virt.h | 1 + 4 files changed, 48 insertions(+), 3 deletions(-)
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>
---
Changes in v2:
- Renamed property from virtio-transports to virtio-mmio-transports
- Added documentation in docs/system/arm/virt.rst
docs/system/arm/virt.rst | 5 +++++
hw/arm/virt-acpi-build.c | 2 +-
hw/arm/virt.c | 43 ++++++++++++++++++++++++++++++++++++++--
include/hw/arm/virt.h | 1 +
4 files changed, 48 insertions(+), 3 deletions(-)
diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst
index e5570773ba..e037f2c269 100644
--- a/docs/system/arm/virt.rst
+++ b/docs/system/arm/virt.rst
@@ -212,6 +212,11 @@ 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 c145678185..27c007fd62 100644
--- a/hw/arm/virt-acpi-build.c
+++ b/hw/arm/virt-acpi-build.c
@@ -1150,7 +1150,7 @@ 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 390845c503..b1e8ce9723 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -1206,7 +1206,7 @@ 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;
@@ -1221,7 +1221,7 @@ 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;
@@ -2705,6 +2705,36 @@ static void virt_set_highmem_mmio_size(Object *obj, Visitor *v,
extended_memmap[VIRT_HIGH_PCIE_MMIO].size = size;
}
+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_its(Object *obj, Error **errp)
{
VirtMachineState *vms = VIRT_MACHINE(obj);
@@ -3427,6 +3457,13 @@ 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",
@@ -3540,6 +3577,8 @@ 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 3b382bdf49..f898afaa6e 100644
--- a/include/hw/arm/virt.h
+++ b/include/hw/arm/virt.h
@@ -169,6 +169,7 @@ 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;
--
2.53.0On Thu, 19 Feb 2026 at 17:33, Mohammadfaiz Bawa <mbawa@redhat.com> wrote: > > 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> > --- > Changes in v2: > - Renamed property from virtio-transports to virtio-mmio-transports > - Added documentation in docs/system/arm/virt.rst > Applied to target-arm.next, thanks. -- PMM
On Thu, 19 Feb 2026 at 17:33, Mohammadfaiz Bawa <mbawa@redhat.com> wrote: > > 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> > --- > Changes in v2: > - Renamed property from virtio-transports to virtio-mmio-transports > - Added documentation in docs/system/arm/virt.rst Applied to target-arm.next, thanks. -- PMM
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