Re: [PATCH 4/5] iommu/vt-d: Remove domain_update_iommu_snooping()

[Jacob Pan <jacob.jun.pan@intel.com>]

Hi BaoLu,

On Sun, 1 May 2022 19:24:33 +0800, Lu Baolu <baolu.lu@linux.intel.com>
wrote:

> The IOMMU force snooping capability is not required to be consistent
> among all the IOMMUs anymore. Remove force snooping capability check
> in the IOMMU hot-add path and domain_update_iommu_snooping() becomes
> a dead code now.
> 
> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> ---
>  drivers/iommu/intel/iommu.c | 34 +---------------------------------
>  1 file changed, 1 insertion(+), 33 deletions(-)
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 3c1c228f9031..d5808495eb64 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -533,33 +533,6 @@ static void domain_update_iommu_coherency(struct
> dmar_domain *domain) rcu_read_unlock();
>  }
>  
> -static bool domain_update_iommu_snooping(struct intel_iommu *skip)
> -{
> -	struct dmar_drhd_unit *drhd;
> -	struct intel_iommu *iommu;
> -	bool ret = true;
> -
> -	rcu_read_lock();
> -	for_each_active_iommu(iommu, drhd) {
> -		if (iommu != skip) {
> -			/*
> -			 * If the hardware is operating in the scalable
> mode,
> -			 * the snooping control is always supported
> since we
> -			 * always set PASID-table-entry.PGSNP bit if the
> domain
> -			 * is managed outside (UNMANAGED).
> -			 */
> -			if (!sm_supported(iommu) &&
> -			    !ecap_sc_support(iommu->ecap)) {
> -				ret = false;
> -				break;
> -			}
> -		}
> -	}
> -	rcu_read_unlock();
> -
> -	return ret;
> -}
> -
>  static int domain_update_iommu_superpage(struct dmar_domain *domain,
>  					 struct intel_iommu *skip)
>  {
> @@ -3593,12 +3566,7 @@ static int intel_iommu_add(struct dmar_drhd_unit
> *dmaru) iommu->name);
>  		return -ENXIO;
>  	}
> -	if (!ecap_sc_support(iommu->ecap) &&
> -	    domain_update_iommu_snooping(iommu)) {
> -		pr_warn("%s: Doesn't support snooping.\n",
> -			iommu->name);
> -		return -ENXIO;
> -	}
> +
Maybe I missed earlier patches, so this bit can also be deleted?

struct dmar_domain {
	u8 iommu_snooping: 1;		/* indicate snooping control
feature */

>  	sp = domain_update_iommu_superpage(NULL, iommu) - 1;
>  	if (sp >= 0 && !(cap_super_page_val(iommu->cap) & (1 << sp))) {
>  		pr_warn("%s: Doesn't support large page.\n",


Thanks,

Jacob