Re: [PATCH] iommu/arm-smmu-v3: Add missing S2FWB feature detection

[Pranjal Shrivastava <praan@google.com>]

On Tue, Apr 08, 2025 at 09:03:51AM +0530, Aneesh Kumar K.V (Arm) wrote:
> Commit 67e4fe398513 ("iommu/arm-smmu-v3: Use S2FWB for NESTED domains")
> introduced S2FWB usage but omitted the corresponding feature detection.
> As a result, vIOMMU allocation fails on FVP in arm_vsmmu_alloc(), due to
> the following check:
> 
> 	if (!arm_smmu_master_canwbs(master) &&
> 	    !(smmu->features & ARM_SMMU_FEAT_S2FWB))
> 		return ERR_PTR(-EOPNOTSUPP);
> 
> This patch adds the missing detection logic to prevent allocation
> failure when S2FWB is supported.
> 
> Fixes: 67e4fe398513 ("iommu/arm-smmu-v3: Use S2FWB for NESTED domains")
> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> index 358072b4e293..c7d297ceabdb 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/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);

Indeed. Looks like setting the feature flag was missed previously.

Reviewed-by: Pranjal Shrivastava <praan@google.com>

Thanks,
Praan