Re: [PATCH 3/5] iommu/vt-d: Check domain force_snooping against attached devices

[Baolu Lu]

On 2022/5/2 21:17, Jason Gunthorpe wrote:
> On Sun, May 01, 2022 at 07:24:32PM +0800, Lu Baolu wrote:
> > +static bool domain_support_force_snooping(struct dmar_domain *domain)
> > +{
> > +	struct device_domain_info *info;
> > +	unsigned long flags;
> > +	bool support = true;
> > +
> > +	spin_lock_irqsave(&device_domain_lock, flags);
> > +	if (list_empty(&domain->devices))
> > +		goto out;
>
> Why? list_for_each_entry will just do nothing..

Yes. I will remove above two lines.

> > +	list_for_each_entry(info, &domain->devices, link) {
> > +		if (!ecap_sc_support(info->iommu->ecap)) {
> > +			support = false;
> > +			break;
> > +		}
> > +	}
> > +out:
> > +	spin_unlock_irqrestore(&device_domain_lock, flags);
> > +	return support;
> > +}
> > +
> > +static void domain_set_force_snooping(struct dmar_domain *domain)
> > +{
> > +	struct device_domain_info *info;
> > +	unsigned long flags;
> > +
> > +	/*
> > +	 * Second level page table supports per-PTE snoop control. The
> > +	 * iommu_map() interface will handle this by setting SNP bit.
> > +	 */
> > +	if (!domain_use_first_level(domain))
> > +		return;
> > +
> > +	spin_lock_irqsave(&device_domain_lock, flags);
> > +	if (list_empty(&domain->devices))
> > +		goto out_unlock;
> > +
> > +	list_for_each_entry(info, &domain->devices, link)
> > +		intel_pasid_setup_page_snoop_control(info->iommu, info->dev,
> > +						     PASID_RID2PASID);
> > +
> > +out_unlock:
> > +	spin_unlock_irqrestore(&device_domain_lock, flags);
> > +}
> > +
> >   static bool intel_iommu_enforce_cache_coherency(struct iommu_domain *domain)
> >   {
> >   	struct dmar_domain *dmar_domain = to_dmar_domain(domain);
> >   
> > -	if (!domain_update_iommu_snooping(NULL))
> > +	if (!domain_support_force_snooping(dmar_domain))
> >   		return false;
>
> Maybe exit early if force_snooping = true?

Yes, should check "force_snooping = true" and return directly if
force_snooping has already been set. As you pointed below, the new
domain_attach should take care of this flag as well. Thanks!

> > +	domain_set_force_snooping(dmar_domain);
> >   	dmar_domain->force_snooping = true;
> > +
> >   	return true;
> >   }
> >   
> > diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
> > index f8d215d85695..815c744e6a34 100644
> > +++ b/drivers/iommu/intel/pasid.c
> > @@ -762,3 +762,21 @@ int intel_pasid_setup_pass_through(struct intel_iommu *iommu,
> >   
> >   	return 0;
> >   }
> > +
> > +/*
> > + * Set the page snoop control for a pasid entry which has been set up.
> > + */
>
> So the 'first level' is only used with pasid?

Yes. A fake pasid (RID2PASID in spec) is used for legacy transactions
(those w/o pasid).

> > +void intel_pasid_setup_page_snoop_control(struct intel_iommu *iommu,
> > +					  struct device *dev, u32 pasid)
> > +{
> > +	struct pasid_entry *pte;
> > +	u16 did;
> > +
> > +	pte = intel_pasid_get_entry(dev, pasid);
> > +	if (WARN_ON(!pte || !pasid_pte_is_present(pte)))
> > +		return;
> > +
> > +	pasid_set_pgsnp(pte);
>
> Doesn't this need to be done in other places too, like when a new attach
> is made? Patch 5 removed it, but should that be made if
> domain->force_snooping?

Yes. I missed this. Will take care of this in the next version.

> Jason

Best regards,
baolu