On 3/11/25 3:10 PM, Shameer Kolothum wrote:
> From: Nicolin Chen <nicol...@nvidia.com>
>
> When nested translation is enabled, there are 2-stage translation
> occuring to two different address spaces: stage-1 in the iommu as,
> while stage-2 in the system as.
>
> If a device attached to the vSMMU doesn't enable stage-1 translation,
> e.g. vSTE sets to Config=Bypass, the system as should be returned,
> so QEMU can set up system memory mappings onto the stage-2 page table.
> This is crucial for an iommufd enabled VFIO device as the VFIO core
> code would register an iommu notifier and replay the address space
> which should be bypassed for this nested translation case.
I would suggest to get inspired of 90519b90539 ("virtio-iommu: Add
bypass mode support to assigned device") or similar patch on vtd
(558e0024a428 intel_iommu: allow dynamic switch of IOMMU region +
4b519ef1de9a intel-iommu: optimize nodmar memory regions), ie. use the
same terminology and techniques/objects (switch_address_space) .
To me this is not related to HW acceleration but rather to VFIO in general.
>
> Signed-off-by: Nicolin Chen <nicol...@nvidia.com>
> Signed-off-by: Shameer Kolothum <shameerali.kolothum.th...@huawei.com>
> ---
> hw/arm/smmuv3-accel.c | 22 +++++++++++++++++++++-
> include/hw/arm/smmuv3-accel.h | 3 +++
> 2 files changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/hw/arm/smmuv3-accel.c b/hw/arm/smmuv3-accel.c
> index 056bd23b2e..76134d106a 100644
> --- a/hw/arm/smmuv3-accel.c
> +++ b/hw/arm/smmuv3-accel.c
> @@ -18,6 +18,7 @@
> static SMMUv3AccelDevice *smmuv3_accel_get_dev(SMMUState *s, SMMUPciBus
> *sbus,
> PCIBus *bus, int devfn)
> {
> + SMMUv3AccelState *s_accel = ARM_SMMUV3_ACCEL(s);
> SMMUDevice *sdev = sbus->pbdev[devfn];
> SMMUv3AccelDevice *accel_dev;
>
> @@ -29,6 +30,8 @@ static SMMUv3AccelDevice *smmuv3_accel_get_dev(SMMUState
> *s, SMMUPciBus *sbus,
>
> sbus->pbdev[devfn] = sdev;
> smmu_init_sdev(s, sdev, bus, devfn);
> + address_space_init(&accel_dev->as_sysmem, &s_accel->root,
> + "smmuv3-accel-sysmem");
> }
>
> return accel_dev;
> @@ -351,12 +354,23 @@ static AddressSpace *smmuv3_accel_find_add_as(PCIBus
> *bus, void *opaque,
> SMMUPciBus *sbus;
> SMMUv3AccelDevice *accel_dev;
> SMMUDevice *sdev;
> + PCIDevice *pdev = pci_find_device(bus, pci_bus_num(bus), devfn);
> + bool has_iommufd = false;
> +
> + if (pdev) {
> + has_iommufd = object_property_find(OBJECT(pdev), "iommufd");
> + }
Refering to the discussion we had on how to set MSI RESV regions at
virt-acpi-build level depending on whether the SMMU was accelerated I
think we can use exactly the above method (checking accel property)
>
> sbus = smmu_get_sbus(s, bus);
> accel_dev = smmuv3_accel_get_dev(s, sbus, bus, devfn);
> sdev = &accel_dev->sdev;
>
> - return &sdev->as;
> + /* Return the system as if the device uses stage-2 only */
> + if (has_iommufd && !accel_dev->s1_hwpt) {
> + return &accel_dev->as_sysmem;
> + } else {
> + return &sdev->as;
> + }
> }
>
> static int smmuv3_accel_pxb_pcie_bus(Object *obj, void *opaque)
> @@ -390,6 +404,12 @@ static void smmu_accel_realize(DeviceState *d, Error
> **errp)
> error_propagate(errp, local_err);
> return;
> }
> +
> + memory_region_init(&s_accel->root, OBJECT(s_accel), "root", UINT64_MAX);
> + memory_region_init_alias(&s_accel->sysmem, OBJECT(s_accel),
> + "smmuv3-accel-sysmem", get_system_memory(), 0,
> + memory_region_size(get_system_memory()));
> + memory_region_add_subregion(&s_accel->root, 0, &s_accel->sysmem);
> bs->get_address_space = smmuv3_accel_find_add_as;
> bs->set_iommu_device = smmuv3_accel_set_iommu_device;
> bs->unset_iommu_device = smmuv3_accel_unset_iommu_device;
> diff --git a/include/hw/arm/smmuv3-accel.h b/include/hw/arm/smmuv3-accel.h
> index 54b217ab4f..58e68534c0 100644
> --- a/include/hw/arm/smmuv3-accel.h
> +++ b/include/hw/arm/smmuv3-accel.h
> @@ -51,12 +51,15 @@ typedef struct SMMUv3AccelDevice {
> SMMUS1Hwpt *s1_hwpt;
> SMMUViommu *viommu;
> SMMUVdev *vdev;
> + AddressSpace as_sysmem;
> QLIST_ENTRY(SMMUv3AccelDevice) next;
> } SMMUv3AccelDevice;
>
> struct SMMUv3AccelState {
> SMMUv3State smmuv3_state;
> SMMUViommu *viommu;
> + MemoryRegion root;
> + MemoryRegion sysmem;
> };
>
> struct SMMUv3AccelClass {
