RE: [PATCH v2 3/4] iommu/vt-d: Remove domain_update_iommu_snooping()

[Tian, Kevin]

> From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> Sent: Thursday, May 5, 2022 9:07 AM
> 
> 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@xxxxxxxxxxxxxxx>
> Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>

> ---
>  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 98112228ae93..da4bfb34ae4b 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;
> -	}
> +
>  	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",
> --
> 2.25.1