Re: [RFC PATCH v2 14/22] iommufd: Add TIO calls

[Jason Gunthorpe <jgg@ziepe.ca>]

On Mon, Apr 07, 2025 at 05:10:29PM +0530, Aneesh Kumar K.V wrote:
> I was trying to prototype this using kvmtool and I have run into some
> issues. First i needed the below change for vIOMMU alloc to work
> 
> modified   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -4405,6 +4405,8 @@ static int arm_smmu_device_hw_probe(struct arm_smmu_device *smmu)
>  	reg = readl_relaxed(smmu->base + ARM_SMMU_IDR3);
>  	if (FIELD_GET(IDR3_RIL, reg))
>  		smmu->features |= ARM_SMMU_FEAT_RANGE_INV;
> +	if (FIELD_GET(IDR3_FWB, reg))
> +		smmu->features |= ARM_SMMU_FEAT_S2FWB;
>  
>  	/* IDR5 */
>  	reg = readl_relaxed(smmu->base + ARM_SMMU_IDR5);

Oh wow, I don't know what happened there that the IDR3 got dropped
maybe a rebase mistake? It was in earlier versions of the patch at
least :\ Please send a formal patch!!

> Also current code don't allow a Stage 1 bypass, Stage2 translation when
> allocating HWPT.
>
> arm_vsmmu_alloc_domain_nested -> arm_smmu_validate_vste -> 
> 
> 	cfg = FIELD_GET(STRTAB_STE_0_CFG, le64_to_cpu(arg->ste[0]));
> 	if (cfg != STRTAB_STE_0_CFG_ABORT && cfg != STRTAB_STE_0_CFG_BYPASS &&
> 	    cfg != STRTAB_STE_0_CFG_S1_TRANS)
> 		return -EIO;
> 
> This only allow a abort or bypass or stage1 translate/stage2 bypass config

The above is for the vSTE, the cfg is not copied as is to the host
STE. See how arm_smmu_make_nested_domain_ste() transforms it.

STRTAB_STE_0_CFG_ABORT blocks all DMA
STRTAB_STE_0_CFG_BYPASS "bypass" for the VM is S2 translation only
STRTAB_STE_0_CFG_S1_TRANS "s1 only" for the VM is S1 & S1 translation

> Also if we don't need stage1 table, what will
> iommufd_viommu_alloc_hwpt_nested() return?

A wrapper around whatever STE configuration that userspace requested
logically linked to the viommu.

Jason