On 11/20/25 14:22, Shameer Kolothum wrote:
> Introduce an “accel” property to enable accelerator mode.
>
> Live migration is currently unsupported when accelerator mode is enabled,
> so a migration blocker is added.
>
> Because this mode relies on IORT RMR for MSI support, accelerator mode is
> not supported for device tree boot.
>
> Also, in the accelerated SMMUv3 case, the host SMMUv3 is configured in nested
> mode (S1 + S2), and the guest owns the Stage-1 page table. Therefore, we
> expose only Stage-1 to the guest to ensure it uses the correct page table
> format.
>
> Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
> Reviewed-by: Eric Auger <eric.auger@redhat.com>
> Tested-by: Zhangfei Gao <zhangfei.gao@linaro.org>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
> Signed-off-by: Shameer Kolothum <skolothumtho@nvidia.com>
> ---
> hw/arm/smmuv3.c | 26 ++++++++++++++++++++++++++
> hw/arm/virt-acpi-build.c | 4 +---
> hw/arm/virt.c | 15 +++++++++++----
> include/hw/arm/smmuv3.h | 1 +
> 4 files changed, 39 insertions(+), 7 deletions(-)
>
> diff --git a/hw/arm/smmuv3.c b/hw/arm/smmuv3.c
> index dba5abc8d3..8352dd5757 100644
> --- a/hw/arm/smmuv3.c
> +++ b/hw/arm/smmuv3.c
> @@ -20,6 +20,7 @@
> #include "qemu/bitops.h"
> #include "hw/irq.h"
> #include "hw/sysbus.h"
> +#include "migration/blocker.h"
> #include "migration/vmstate.h"
> #include "hw/qdev-properties.h"
> #include "hw/qdev-core.h"
> @@ -1915,6 +1916,17 @@ static void smmu_reset_exit(Object *obj, ResetType type)
> smmuv3_accel_reset(s);
> }
>
> +static bool smmu_validate_property(SMMUv3State *s, Error **errp)
> +{
> +#ifndef CONFIG_ARM_SMMUV3_ACCEL
> + if (s->accel) {
> + error_setg(errp, "accel=on support not compiled in");
> + return false;
> + }
> +#endif
> + return true;
> +}
> +
> static void smmu_realize(DeviceState *d, Error **errp)
> {
> SMMUState *sys = ARM_SMMU(d);
> @@ -1923,8 +1935,17 @@ static void smmu_realize(DeviceState *d, Error **errp)
> SysBusDevice *dev = SYS_BUS_DEVICE(d);
> Error *local_err = NULL;
>
> + if (!smmu_validate_property(s, errp)) {
> + return;
> + }
You should really consider adding a new QOM model for the "accel" mode.
> if (s->accel) {
> smmuv3_accel_init(s);
> + error_setg(&s->migration_blocker, "Migration not supported with SMMUv3 "
> + "accelerator mode enabled");
> + if (migrate_add_blocker(&s->migration_blocker, errp) < 0) {
> + return;
> + }
I would add the migration blocker in a separate patch.
> }
>
> c->parent_realize(d, &local_err);
> @@ -2023,6 +2044,7 @@ static const Property smmuv3_properties[] = {
> * Defaults to stage 1
> */
> DEFINE_PROP_STRING("stage", SMMUv3State, stage),
> + DEFINE_PROP_BOOL("accel", SMMUv3State, accel, false),
> /* GPA of MSI doorbell, for SMMUv3 accel use. */
> DEFINE_PROP_UINT64("msi-gpa", SMMUv3State, msi_gpa, 0),
> };
> @@ -2046,6 +2068,10 @@ static void smmuv3_class_init(ObjectClass *klass, const void *data)
> device_class_set_props(dc, smmuv3_properties);
> dc->hotpluggable = false;
> dc->user_creatable = true;
> +
> + object_class_property_set_description(klass, "accel",
> + "Enable SMMUv3 accelerator support. Allows host SMMUv3 to be "
> + "configured in nested mode for vfio-pci dev assignment");
> }
>
> static int smmuv3_notify_flag_changed(IOMMUMemoryRegion *iommu,
> diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c
> index 7a7b2e62c1..fd78c39317 100644
> --- a/hw/arm/virt-acpi-build.c
> +++ b/hw/arm/virt-acpi-build.c
> @@ -400,9 +400,7 @@ static int iort_smmuv3_devices(Object *obj, void *opaque)
> }
>
> bus = PCI_BUS(object_property_get_link(obj, "primary-bus", &error_abort));
> - if (object_property_find(obj, "accel")) {
> - sdev.accel = object_property_get_bool(obj, "accel", &error_abort);
> - }
> + sdev.accel = object_property_get_bool(obj, "accel", &error_abort);
> pbus = PLATFORM_BUS_DEVICE(vms->platform_bus_dev);
> sbdev = SYS_BUS_DEVICE(obj);
> sdev.base = platform_bus_get_mmio_addr(pbus, sbdev, 0);
> diff --git a/hw/arm/virt.c b/hw/arm/virt.c
> index 8503879c3d..51b15aef37 100644
> --- a/hw/arm/virt.c
> +++ b/hw/arm/virt.c
> @@ -3052,13 +3052,21 @@ static void virt_machine_device_pre_plug_cb(HotplugHandler *hotplug_dev,
> /* The new SMMUv3 device is specific to the PCI bus */
> object_property_set_bool(OBJECT(dev), "smmu_per_bus", true, NULL);
> }
> - if (object_property_find(OBJECT(dev), "accel") &&
> - object_property_get_bool(OBJECT(dev), "accel", &error_abort)) {
> + if (object_property_get_bool(OBJECT(dev), "accel", &error_abort)) {
> + char *stage;
> +
> if (!kvm_enabled() || !kvm_irqchip_in_kernel()) {
> error_setg(errp, "SMMUv3 accel=on requires KVM with "
> "kernel-irqchip=on support");
> return;
> }
> + stage = object_property_get_str(OBJECT(dev), "stage", &error_fatal);
> + /* If no stage specified, SMMUv3 will default to stage 1 */
> + if (*stage && strcmp("1", stage)) {
It would be less "ugly" to check SMMUStage enum values instead
of using string compare :/
> + error_setg(errp, "Only stage1 is supported for SMMUV3 with "
> + "accel=on");
Can't this condition be checked in the realize handler instead ?
C.
> + return;
> + }
> }
> }
> }
> @@ -3096,8 +3104,7 @@ static void virt_machine_device_plug_cb(HotplugHandler *hotplug_dev,
> }
>
> create_smmuv3_dev_dtb(vms, dev, bus);
> - if (object_property_find(OBJECT(dev), "accel") &&
> - object_property_get_bool(OBJECT(dev), "accel", &error_abort)) {
> + if (object_property_get_bool(OBJECT(dev), "accel", &error_abort)) {
> hwaddr db_start;
>
> if (vms->msi_controller == VIRT_MSI_CTRL_ITS) {
> diff --git a/include/hw/arm/smmuv3.h b/include/hw/arm/smmuv3.h
> index 5616a8a2be..9c39acd5ca 100644
> --- a/include/hw/arm/smmuv3.h
> +++ b/include/hw/arm/smmuv3.h
> @@ -68,6 +68,7 @@ struct SMMUv3State {
> bool accel;
> struct SMMUv3AccelState *s_accel;
> uint64_t msi_gpa;
> + Error *migration_blocker;
> };
>
> typedef enum {