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>
Mohammadfaiz Bawa committed
Feb 26, 2026 at 11:27 UTC
ee4d1ff3af85418a1dd946647658b954649e43ae
4 files changed
+48
-3
docs/system/arm/virt.rst
+5
@@ -226,6 +226,11 @@ dtb-randomness
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dtb-kaslr-seed
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A deprecated synonym for dtb-randomness.
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+virtio-mmio-transports
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+ Set the number of virtio-mmio transports to create (between 0 and 32;
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+ the default is 32). Unused transports are harmless, but you can
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+ use this property to avoid exposing them to the guest if you wish.
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+
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x-oem-id
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Set string (up to 6 bytes) to override the default value of field OEMID in ACPI
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table header.
hw/arm/virt-acpi-build.c
+1
-1
@@ -1154,7 +1154,7 @@ build_dsdt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
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fw_cfg_acpi_dsdt_add(scope, &memmap[VIRT_FW_CFG]);
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virtio_acpi_dsdt_add(scope, memmap[VIRT_MMIO].base, memmap[VIRT_MMIO].size,
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(irqmap[VIRT_MMIO] + ARM_SPI_BASE),
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- 0, NUM_VIRTIO_TRANSPORTS);
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+ 0, vms->virtio_transports);
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acpi_dsdt_add_pci(scope, memmap, irqmap[VIRT_PCIE] + ARM_SPI_BASE, vms);
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if (vms->acpi_dev) {
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build_ged_aml(scope, "\\_SB."GED_DEVICE,
hw/arm/virt.c
+41
-2
@@ -1208,7 +1208,7 @@ static void create_virtio_devices(const VirtMachineState *vms)
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* between kernel versions). For reliable and stable identification
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* of disks users must use UUIDs or similar mechanisms.
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*/
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- for (i = 0; i < NUM_VIRTIO_TRANSPORTS; i++) {
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+ for (i = 0; i < vms->virtio_transports; i++) {
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int irq = vms->irqmap[VIRT_MMIO] + i;
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hwaddr base = vms->memmap[VIRT_MMIO].base + i * size;
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@@ -1223,7 +1223,7 @@ static void create_virtio_devices(const VirtMachineState *vms)
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* loop influences virtio device to virtio transport assignment, whereas
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* this loop controls how virtio transports are laid out in the dtb.
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*/
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- for (i = NUM_VIRTIO_TRANSPORTS - 1; i >= 0; i--) {
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+ for (i = vms->virtio_transports - 1; i >= 0; i--) {
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char *nodename;
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int irq = vms->irqmap[VIRT_MMIO] + i;
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hwaddr base = vms->memmap[VIRT_MMIO].base + i * size;
@@ -2826,6 +2826,36 @@ static void virt_set_its(Object *obj, bool value, Error **errp)
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}
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}
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+static void virt_get_virtio_transports(Object *obj, Visitor *v,
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+ const char *name, void *opaque,
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+ Error **errp)
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+{
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+ VirtMachineState *vms = VIRT_MACHINE(obj);
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+ uint8_t transports = vms->virtio_transports;
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+
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+ visit_type_uint8(v, name, &transports, errp);
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+}
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+
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+static void virt_set_virtio_transports(Object *obj, Visitor *v,
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+ const char *name, void *opaque,
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+ Error **errp)
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+{
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+ VirtMachineState *vms = VIRT_MACHINE(obj);
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+ uint8_t transports;
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+
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+ if (!visit_type_uint8(v, name, &transports, errp)) {
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+ return;
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+ }
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+
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+ if (transports > NUM_VIRTIO_TRANSPORTS) {
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+ error_setg(errp, "virtio-mmio-transports must not exceed %d",
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+ NUM_VIRTIO_TRANSPORTS);
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+ return;
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+ }
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+
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+ vms->virtio_transports = transports;
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+}
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+
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static bool virt_get_dtb_randomness(Object *obj, Error **errp)
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{
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VirtMachineState *vms = VIRT_MACHINE(obj);
@@ -3535,6 +3565,13 @@ static void virt_machine_class_init(ObjectClass *oc, const void *data)
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"Set the high memory region size "
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"for PCI MMIO");
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+ object_class_property_add(oc, "virtio-mmio-transports", "uint8",
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+ virt_get_virtio_transports,
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+ virt_set_virtio_transports,
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+ NULL, NULL);
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+ object_class_property_set_description(oc, "virtio-mmio-transports",
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+ "Set the number of virtio-mmio transports to instantiate");
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+
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object_class_property_add_str(oc, "gic-version", virt_get_gic_version,
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virt_set_gic_version);
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object_class_property_set_description(oc, "gic-version",
@@ -3654,6 +3691,8 @@ static void virt_instance_init(Object *obj)
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vms->irqmap = a15irqmap;
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+ vms->virtio_transports = NUM_VIRTIO_TRANSPORTS;
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+
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virt_flash_create(vms);
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vms->oem_id = g_strndup(ACPI_BUILD_APPNAME6, 6);
include/hw/arm/virt.h
+1
@@ -172,6 +172,7 @@ struct VirtMachineState {
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uint32_t msi_phandle;
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uint32_t iommu_phandle;
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int psci_conduit;
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+ uint8_t virtio_transports;
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hwaddr highest_gpa;
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DeviceState *gic;
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DeviceState *acpi_dev;