RE: [PATCH 1/1] iommu/vt-d: Support asynchronous IOMMU nested capabilities

["Tian, Kevin" <kevin.tian@intel.com>]

> From: Lu Baolu <baolu.lu@linux.intel.com>
> Sent: Wednesday, May 12, 2021 3:04 PM
> 
> Current VT-d implementation supports nested translation only if all
> underlying IOMMUs support the nested capability. This is unnecessary
> as the upper layer is allowed to create different containers and set
> them with different type of iommu backend. The IOMMU driver needs to
> guarantee that devices attached to a nested mode iommu_domain should
> support nested capabilility.

so the consistency check is now applied only to the IOMMUs that are 
spanned by a given iommu_domain?

> 
> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> ---
>  drivers/iommu/intel/iommu.c | 21 +++++++++++++++++++--
>  1 file changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index f1742da42478..1cd4840e6f9f 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -4755,6 +4755,13 @@ static int prepare_domain_attach_device(struct
> iommu_domain *domain,
>  	if (!iommu)
>  		return -ENODEV;
> 
> +	if ((dmar_domain->flags & DOMAIN_FLAG_NESTING_MODE) &&
> +	    !ecap_nest(iommu->ecap)) {
> +		dev_err(dev, "%s: iommu not support nested translation\n",
> +			iommu->name);
> +		return -EINVAL;
> +	}
> +
>  	/* check if this iommu agaw is sufficient for max mapped address */
>  	addr_width = agaw_to_width(iommu->agaw);
>  	if (addr_width > cap_mgaw(iommu->cap))
> @@ -5451,11 +5458,21 @@ static int
>  intel_iommu_enable_nesting(struct iommu_domain *domain)
>  {
>  	struct dmar_domain *dmar_domain = to_dmar_domain(domain);
> +	struct dmar_drhd_unit *drhd;
> +	struct intel_iommu *iommu;
> +	bool has_nesting = false;
>  	unsigned long flags;
> -	int ret = -ENODEV;
> +	int ret = -EINVAL;
> +
> +	for_each_active_iommu(iommu, drhd)
> +		if (ecap_nest(iommu->ecap))
> +			has_nesting = true;
> +
> +	if (!has_nesting)
> +		return -ENODEV;

Isn't above still doing global consistency check?

> 
>  	spin_lock_irqsave(&device_domain_lock, flags);
> -	if (nested_mode_support() && list_empty(&dmar_domain->devices))
> {
> +	if (list_empty(&dmar_domain->devices)) {
>  		dmar_domain->flags |= DOMAIN_FLAG_NESTING_MODE;
>  		dmar_domain->flags &= ~DOMAIN_FLAG_USE_FIRST_LEVEL;
>  		ret = 0;
> --
> 2.25.1