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

[Baolu Lu]

On 2022/5/3 05:36, Jacob Pan wrote:
> Hi BaoLu,
>
> On Sun, 1 May 2022 19:24:33 +0800, Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> 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@xxxxxxxxxxxxxxx>
> > ---
> >   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 */

It has been cleaned up by below commit:

71cfafda9c9b vfio: Move the Intel no-snoop control off of IOMMU_CACHE

> >   	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

Best regards,
baolu