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

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