Re: [PATCH v9 16/25] iommu/arm-smmu-v3-kvm: Emulate CMDQ for host

[Nicolin Chen]

On Thu, Oct 15, 2026 at 08:08:47PM +0000, Mostafa Saleh wrote:
> @@ -385,18 +482,51 @@ static bool smmu_dabt_device(struct hyp_arm_smmu_v3_device *smmu,
>  		 */
>  		mask = read_only & ~(IDR0_S2P | IDR0_VMID16 | IDR0_MSI | IDR0_HYP | IDR0_ATS);
>  		break;
> -	/* Passthrough the register access for bisectability, handled later */
>  	case ARM_SMMU_CMDQ_BASE:
> +		/*
> +		 * Although allowed to use smaller size, we rely on the SMMUv3 driver
> +		 * using 64-bit store instruction for simplicity.
> +		 */
> +		if (len != sizeof(u64))
> +			break;
>  		if (is_write) {
>  			/* Not allowed by the architecture */
>  			if (is_cmdq_enabled(smmu))

The spec says the register is RO when CMDQEN=0. So, maybe it should
be allowed by just ignoring the write?

>  	case ARM_SMMU_CMDQ_CONS:
> +		if (len != sizeof(u32))
> +			break;
> +		if (is_write) {
> +			if (WARN_ON(is_cmdq_enabled(smmu)))
> +				break;

Ditto

Nicolin