linux-kernel - Re: [PATCH 3/5] iommu/vt-d: Check domain force

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Date:   Mon, 2 May 2022 10:17:47 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [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