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

[Baolu Lu <baolu.lu@linux.intel.com>]

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