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

[Jacob Pan]

Hi BaoLu,

On Sun, 1 May 2022 19:24:32 +0800, Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
wrote:

> As domain->force_snooping only impacts the devices attached with the
> domain, there's no need to check against all IOMMU units. At the same
> time, for a brand new domain (hasn't been attached to any device), the
> force_snooping field could be set, but the attach_dev callback will
> return failure if it wants to attach to a device which IOMMU has no
> snoop control capability.
> 
> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> ---
>  drivers/iommu/intel/pasid.h |  2 ++
>  drivers/iommu/intel/iommu.c | 50 ++++++++++++++++++++++++++++++++++++-
>  drivers/iommu/intel/pasid.c | 18 +++++++++++++
>  3 files changed, 69 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/intel/pasid.h b/drivers/iommu/intel/pasid.h
> index ab4408c824a5..583ea67fc783 100644
> --- a/drivers/iommu/intel/pasid.h
> +++ b/drivers/iommu/intel/pasid.h
> @@ -123,4 +123,6 @@ void intel_pasid_tear_down_entry(struct intel_iommu
> *iommu, bool fault_ignore);
>  int vcmd_alloc_pasid(struct intel_iommu *iommu, u32 *pasid);
>  void vcmd_free_pasid(struct intel_iommu *iommu, u32 pasid);
> +void intel_pasid_setup_page_snoop_control(struct intel_iommu *iommu,
> +					  struct device *dev, u32 pasid);
>  #endif /* __INTEL_PASID_H */
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 98050943d863..3c1c228f9031 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -4554,13 +4554,61 @@ static phys_addr_t
> intel_iommu_iova_to_phys(struct iommu_domain *domain, return phys;
>  }
>  
> +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;
> +
> +	list_for_each_entry(info, &domain->devices, link) {
> +		if (!ecap_sc_support(info->iommu->ecap)) {
> +			support = false;
> +			break;
> +		}
> +	}
why not just check the flag dmar_domain->force_snooping? devices wouldn't
be able to attach if !ecap_sc, right?

> +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);
> +
I guess other DMA API PASIDs need to have sc bit set as well. I will keep
this in mind for my DMA API PASID patch.

> +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;
> +
> +	domain_set_force_snooping(dmar_domain);
>  	dmar_domain->force_snooping = true;
> +
nit: spurious change
>  	return true;
>  }
>  
> diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
> index f8d215d85695..815c744e6a34 100644
> --- a/drivers/iommu/intel/pasid.c
> +++ 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.
> + */
> +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);
> +	did = pasid_get_domain_id(pte);
> +	pasid_flush_caches(iommu, pte, pasid, did);
> +}


Thanks,

Jacob