Re: [RFC PATCH v4 03/16] iommu/arm-smmu-v3: Add initial pSMMU realm viommu plumbing

[Aneesh Kumar K.V <aneesh.kumar@kernel.org>]

Nicolin Chen <nicolinc@nvidia.com> writes:

> On Tue, Sep 01, 2026 at 11:34:45AM -0300, Jason Gunthorpe wrote:
>> On Tue, Sep 01, 2026 at 03:36:37PM +0530, Aneesh Kumar K.V wrote:
>> 
>> > @@ -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);
>> > +
>> 
>> I think the realm vsmmu is going to require a different info struct
>> than the normal psmmu case, isn't it?
>> 
>> If so it needs its own enum value.
>> 
>> It would be nice to see a draft patch showing how the real vsmmu works
>> on top of the RMM spec for it. If we are using a viommu object then
>> non-vsmmu case should be identical just with an option in the info
>> struct to not create the vsmmu object.
>
> Actually, the PSMMU-only viommu object in this series only adds a
> type with no viommu data structure.
>
> I've drafted the vsmmu case on top of the series, so it would add
> a structure reusing the same IOMMU_VIOMMU_TYPE_ARM_SMMUV3 with a
> flag:
>
> +/**
> + * enum iommu_viommu_arm_realm_vsmmuv3_flags - Flags for ARM SMMUv3 Realm
> + * @IOMMU_VIOMMU_ARM_REALM_SMMUV3_FLAGS_VSMMU: Indicates whether the Realm has
> + *                                             a guest-visible VSMMU instance
> + */
> +enum iommu_viommu_arm_realm_vsmmuv3_flags {
> +	IOMMU_VIOMMU_ARM_REALM_SMMUV3_FLAGS_VSMMU = 1 << 0,
> +};
> +
> +/**
> + * struct iommu_viommu_arm_realm_vsmmuv3 - ARM Realm VSMMUv3 parameters
> + *                                         (IOMMU_VIOMMU_TYPE_ARM_REALM_SMMUV3)
> + * @flags: Combination of enum iommu_viommu_arm_realm_vsmmuv3_flags
> + * @reg_base: MMIO base address of the VSMMU in the guest VM
> + * @reg_top: MMIO top address of the VSMMU in the guest VM
> + * @aidr: AIDR register value of the VSMMU in the guest VM
> + * @idr: IDR register values of the VSMMU in the guest VM
> + */
> +struct iommu_viommu_arm_realm_vsmmuv3 {
> +	__aligned_u64 flags;
> +	__aligned_le64 reg_base;
> +	__aligned_le64 reg_top;
> +	__aligned_le64 aidr;
> +	__aligned_le64 idr[7];
> +};
>
> I think this should work. But I still feel awkward that a non-vsmmu
> case has to allocate a viommu object for a set of RMI commands that
> don't need an Realm Descriptor. Things could be cleaner if we allow
> RMI_PSMMU_ACTIVATE and RMI_PSMMU_ST_L2_CREATE to be independent on
> a viommu; then leave IOMMU_VIOMMU_TYPE_ARM_SMMUV3 to vsmmu-visiable
> case.
 
RMI_VSMMU_CREATE requires an RD, RD won't be available during
viomm_alloc right?

-aneesh