Re: [PATCH v9 14/25] iommu/arm-smmu-v3-kvm: Shadow the command queue

[Nicolin Chen]

On Thu, Oct 15, 2026 at 08:08:45PM +0000, Mostafa Saleh wrote:
> At boot, allocate a command queue per SMMU which is used as a shadow
> by the hypervisor.
> 
> The command queue size is 64K which is more than enough, as the
> hypervisor would consume all the entries per a command queue prod
> write, which means it can handle up to 4096 at a time.
> 
> Then, the host command queue needs to be pinned in a shared state, so
> it can't be donated to VMs, and avoid tricking the hypervisor into
> accessing them. This is done each time the command queue is enabled,
> and undone each time the command queue is disabled.
> The hypervisor won't access the host command queue when it is disabled
> from the host.
> 
> Signed-off-by: Mostafa Saleh <smostafa@xxxxxxxxxx>

Reviewed-by: Nicolin Chen <nicolinc@xxxxxxxxxx>

With some nits:

> @@ -23,6 +25,15 @@ static size_t kvm_arm_smmu_cur;
>  static void __init kvm_arm_smmu_array_free(void)
>  {
>  	int order;
> +	int i;
> +
> +	for (i = 0 ; i < kvm_arm_smmu_cur ; ++i) {

s/ ;/;/g

> @@ -158,6 +268,14 @@ static bool smmu_dabt_device(struct hyp_arm_smmu_v3_device *smmu,
>  		break;
>  	/* Passthrough the register access for bisectability, handled later */
>  	case ARM_SMMU_CMDQ_BASE:
> +		if (is_write) {
> +			/* Not allowed by the architecture */
> +			if (is_cmdq_enabled(smmu))
> +				break;

Sashiko reported the same WARN_ON issue. You might want to confirm.

> @@ -170,9 +288,16 @@ static bool smmu_dabt_device(struct hyp_arm_smmu_v3_device *smmu,
>  			break;
>  
>  		if (is_write) {
> +			bool last_cmdq_en = is_cmdq_enabled(smmu);

Maybe cmdq_was_enabled (local) and cmdq_is_enabled (helper)

Nicolin