Re: [PATCH v5 27/27] iommu/arm-smmu-v3-kvm: Enable nesting

[Jason Gunthorpe <jgg@ziepe.ca>]

On Mon, Nov 17, 2025 at 06:48:14PM +0000, Mostafa Saleh wrote:
> @@ -441,8 +490,32 @@ static void smmu_reshadow_ste(struct hyp_arm_smmu_v3_device *smmu, u32 sid, bool
>  		hyp_ste_ptr = smmu_get_ste_ptr(smmu, sid, hyp_ste_base);
>  	}
>  
> -	smmu_copy_from_host(smmu, hyp_ste_ptr->data, host_ste_ptr->data,
> +	smmu_copy_from_host(smmu, target.data, host_ste_ptr->data,
>  			    STRTAB_STE_DWORDS << 3);
> +	/*
> +	 * Typically, STE update is done as the following
> +	 * 1- Write last 7 dwords, while STE is invalid
> +	 * 2- CFGI
> +	 * 3- Write first dword, making STE valid
> +	 * 4- CFGI
> +	 * As the SMMU MUST at least load 64 bits atomically
> +	 * that gurantees that there is no race between writing
> +	 * the STE and the CFGI where the SMMU observes parts
> +	 * of the STE.
> +	 * In the shadow we update the STE to enable nested translation,
> +	 * which requires updating first 4 dwords.
> +	 * That is only done if the STE is valid and not in abort.
> +	 * Which means it happens at step 4)
> +	 * So we need to also write the last 7 dwords and send CFGI
> +	 * before writing the first dword.
> +	 * There is no need for last CFGI as it's done next.
> +	 */

This really should share the main driver logic to do STE writes in the
right order and try to avoid making it non-valid if not necessary.

This will not properly support all the real-world kernel flows around
PASID with such a simplistic implementation.

Json