Re: [RFC PATCH v4 03/16] iommu/arm-smmu-v3: Add initial pSMMU realm viommu plumbing
flat view
From: Aneesh Kumar K.V <aneesh.kumar@kernel.org>
Date: 2026-09-01 10:06:45
Also in:
kvmarm, linux-coco, lkml
Aneesh Kumar K.V [off-list ref] writes:
Nicolin Chen [off-list ref] writes:quoted
On Mon, Apr 27, 2026 at 02:23:31PM +0530, Aneesh Kumar K.V (Arm) wrote:
...
quoted
.. and we demand userspace (VMM) to use IOMMU_VIOMMU_ALLOC ioctl, even if VMM does not actually expose a guest-level SMMU instance. Thus, no user_data. I can get the reasoning behind the flow using this viommu/vdevice. But, on the other hand, I can imagine that a Realm VSMMU would add a new flag with a user_data to this VIOMMU. Then, this flow would give some troubles to VMM (QEMU for example): - For VM with a guest-level SMMU, QEMU creates a realm instance where IOMMU_VIOMMU_TYPE_ARM_REALM_SMMUV3 (with vsmmu) can be allocated. - For VM w/o a guest-level SMMU, QEMU won't create such a realm instance, while still required to invoke the ioctl (w/o vsmmu). Taking a step back, I wonder if we really need to use iommufd for PSMMU activation and its stream table allocations? Here are some facts: - An iommufd has a ctx, that's one per VM. Similarly, a Realm has an RD. - For an RMI command that needs an RD, it makes sense to be per iommufd ctx, e.g. RMI_VSMMU_* or RMI_VDEV_* commands. - PSMMU commands are global; they don't need RD. So they don't seem necessary to tie to an iommufd ctx. Instead, could the PSMMU activation be done after RMI_PSMMU_INFO check? Is there any reason not to do that? A safer timing might be at the device assignment stage?One of the reasons I added IOMMU_VIOMMU_TYPE_ARM_REALM_SMMUV3 was to avoid creating a psmmu object when we are not using a PCI passthrough VM. That is also the reason for all the refcounting around the psmmu objects. If we are okay with creating psmmu objects early, then I guess we can go with the above approach.
How about? modified drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-iommufd.c
@@ -437,9 +437,6 @@ if (viommu_type == IOMMU_VIOMMU_TYPE_ARM_SMMUV3) return VIOMMU_STRUCT_SIZE(struct arm_vsmmu, core); - if (viommu_type == IOMMU_VIOMMU_TYPE_ARM_REALM_SMMUV3) - return VIOMMU_STRUCT_SIZE(struct arm_vsmmu, core); - if (!smmu->impl_ops || !smmu->impl_ops->get_viommu_size) return 0; return smmu->impl_ops->get_viommu_size(viommu_type);
@@ -463,14 +460,13 @@ vsmmu->vmid = s2_parent->s2_cfg.vmid; if (viommu->type == IOMMU_VIOMMU_TYPE_ARM_SMMUV3) { + if (arm_smmu_is_realm_viommu(viommu)) + return arm_realm_smmu_v3_init(viommu, user_data); + viommu->ops = &arm_vsmmu_ops; return 0; } - if (viommu->type == IOMMU_VIOMMU_TYPE_ARM_REALM_SMMUV3) - return arm_realm_smmu_v3_init(viommu, user_data); - - return smmu->impl_ops->vsmmu_init(vsmmu, user_data); }
modified drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-realm.c
@@ -239,21 +239,27 @@ return 0; } +bool arm_smmu_is_realm_viommu(struct iommufd_viommu *viommu) +{ + struct kvm *kvm; + + if (!viommu->kvm_file) + return false; + + kvm = viommu->kvm_file->private_data; + return kvm_is_realm(kvm); +} + int arm_realm_smmu_v3_init(struct iommufd_viommu *viommu, const struct iommu_user_data *user_data) { int ret = 0; - struct kvm *kvm; struct rmi_psmmu_params *params; struct arm_smmu_device *smmu = container_of(viommu->iommu_dev, struct arm_smmu_device, iommu); unsigned long rmi_ret; - if (!viommu->kvm_file) - return -EINVAL; - - kvm = viommu->kvm_file->private_data; - if (!kvm_is_realm(kvm)) + if (!arm_smmu_is_realm_viommu(viommu)) return -EINVAL; if (!(smmu->features & ARM_SMMU_FEAT_RME))
modified drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -4515,8 +4515,6 @@ int ret; mutex_init(&smmu->streams_mutex); - mutex_init(&smmu->realm.mutex); - refcount_set(&smmu->realm.users, 0); smmu->streams = RB_ROOT; ret = arm_smmu_init_queues(smmu);
@@ -5578,6 +5576,8 @@ return -ENODEV; } + mutex_init(&smmu->realm.mutex); + refcount_set(&smmu->realm.users, 0); smmu->features |= ARM_SMMU_FEAT_RME_IRQ; return 0;
modified drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
@@ -1282,6 +1282,7 @@ const struct iommu_user_data *user_data); int arm_vsmmu_cache_invalidate(struct iommufd_viommu *viommu, struct iommu_user_data_array *array); +bool arm_smmu_is_realm_viommu(struct iommufd_viommu *viommu); int arm_realm_smmu_v3_init(struct iommufd_viommu *viommu, const struct iommu_user_data *user_data); #else
modified include/uapi/linux/iommufd.h
@@ -1068,7 +1068,6 @@ * VMM must wire the HYP_OWN bit to 0 in guest VINTF_CONFIG register */ IOMMU_VIOMMU_TYPE_TEGRA241_CMDQV = 2, - IOMMU_VIOMMU_TYPE_ARM_REALM_SMMUV3 = 3, }; /**