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

> + 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?

> + 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?

> +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?

Jason

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