RE: [PATCH v4 3/5] iommu/vt-d: Disable non-recoverable fault processing before unbind

["Tian, Kevin" <kevin.tian@intel.com>]

> From: Lu Baolu <baolu.lu@linux.intel.com>
> Sent: Thursday, May 7, 2020 8:56 AM
> 
> When a PASID is used for SVA by the device, it's possible that the PASID
> entry is cleared before the device flushes all ongoing DMA requests. The
> IOMMU should ignore the non-recoverable faults caused by these requests.
> Intel VT-d provides such function through the FPD bit of the PASID entry.
> This sets FPD bit when PASID entry is cleared in the mm notifier and
> clear it when the pasid is unbound.
> 
> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> ---
>  drivers/iommu/intel-iommu.c |  4 ++--
>  drivers/iommu/intel-pasid.c | 26 +++++++++++++++++++++-----
>  drivers/iommu/intel-pasid.h |  3 ++-
>  drivers/iommu/intel-svm.c   |  9 ++++++---
>  4 files changed, 31 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index d1866c0905b1..7811422b5a68 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -5352,7 +5352,7 @@ static void __dmar_remove_one_dev_info(struct
> device_domain_info *info)
>  	if (info->dev) {
>  		if (dev_is_pci(info->dev) && sm_supported(iommu))
>  			intel_pasid_tear_down_entry(iommu, info->dev,
> -					PASID_RID2PASID);
> +					PASID_RID2PASID, false);
> 
>  		iommu_disable_dev_iotlb(info);
>  		domain_context_clear(iommu, info->dev);
> @@ -5587,7 +5587,7 @@ static void aux_domain_remove_dev(struct
> dmar_domain *domain,
>  	auxiliary_unlink_device(domain, dev);
> 
>  	spin_lock(&iommu->lock);
> -	intel_pasid_tear_down_entry(iommu, dev, domain->default_pasid);
> +	intel_pasid_tear_down_entry(iommu, dev, domain->default_pasid,
> false);
>  	domain_detach_iommu(domain, iommu);
>  	spin_unlock(&iommu->lock);
> 
> diff --git a/drivers/iommu/intel-pasid.c b/drivers/iommu/intel-pasid.c
> index 7969e3dac2ad..11aef6c12972 100644
> --- a/drivers/iommu/intel-pasid.c
> +++ b/drivers/iommu/intel-pasid.c
> @@ -292,7 +292,20 @@ static inline void pasid_clear_entry(struct
> pasid_entry *pe)
>  	WRITE_ONCE(pe->val[7], 0);
>  }
> 
> -static void intel_pasid_clear_entry(struct device *dev, int pasid)
> +static inline void pasid_clear_entry_with_fpd(struct pasid_entry *pe)
> +{
> +	WRITE_ONCE(pe->val[0], PASID_PTE_FPD);
> +	WRITE_ONCE(pe->val[1], 0);
> +	WRITE_ONCE(pe->val[2], 0);
> +	WRITE_ONCE(pe->val[3], 0);
> +	WRITE_ONCE(pe->val[4], 0);
> +	WRITE_ONCE(pe->val[5], 0);
> +	WRITE_ONCE(pe->val[6], 0);
> +	WRITE_ONCE(pe->val[7], 0);
> +}
> +
> +static void
> +intel_pasid_clear_entry(struct device *dev, int pasid, bool pf_ignore)

Hi, Baolu,

Just curious whether it makes sense to always set FPD here. Yes, SVA is
one known example that non-recoverable fault associated with a PASID
entry might be caused after the entry is cleared and those are considered
benign.  But even in a general context (w/o SVA) why do we care about 
such faults after a PASID entry is torn down?

Thanks
Kevin

>  {
>  	struct pasid_entry *pe;
> 
> @@ -300,7 +313,10 @@ static void intel_pasid_clear_entry(struct device
> *dev, int pasid)
>  	if (WARN_ON(!pe))
>  		return;
> 
> -	pasid_clear_entry(pe);
> +	if (pf_ignore)
> +		pasid_clear_entry_with_fpd(pe);
> +	else
> +		pasid_clear_entry(pe);
>  }
> 
>  static inline void pasid_set_bits(u64 *ptr, u64 mask, u64 bits)
> @@ -533,8 +549,8 @@ devtlb_invalidation_with_pasid(struct intel_iommu
> *iommu,
>  	qi_flush_dev_iotlb(iommu, sid, pfsid, qdep, 0, 64 - VTD_PAGE_SHIFT);
>  }
> 
> -void intel_pasid_tear_down_entry(struct intel_iommu *iommu,
> -				 struct device *dev, int pasid)
> +void intel_pasid_tear_down_entry(struct intel_iommu *iommu, struct
> device *dev,
> +				 int pasid, bool pf_ignore)
>  {
>  	struct pasid_entry *pte;
>  	u16 did;
> @@ -544,7 +560,7 @@ void intel_pasid_tear_down_entry(struct
> intel_iommu *iommu,
>  		return;
> 
>  	did = pasid_get_domain_id(pte);
> -	intel_pasid_clear_entry(dev, pasid);
> +	intel_pasid_clear_entry(dev, pasid, pf_ignore);
> 
>  	if (!ecap_coherent(iommu->ecap))
>  		clflush_cache_range(pte, sizeof(*pte));
> diff --git a/drivers/iommu/intel-pasid.h b/drivers/iommu/intel-pasid.h
> index a41b09b3ffde..e6dd95ffe381 100644
> --- a/drivers/iommu/intel-pasid.h
> +++ b/drivers/iommu/intel-pasid.h
> @@ -15,6 +15,7 @@
>  #define PASID_MAX			0x100000
>  #define PASID_PTE_MASK			0x3F
>  #define PASID_PTE_PRESENT		1
> +#define PASID_PTE_FPD			2
>  #define PDE_PFN_MASK			PAGE_MASK
>  #define PASID_PDE_SHIFT			6
>  #define MAX_NR_PASID_BITS		20
> @@ -120,7 +121,7 @@ int intel_pasid_setup_nested(struct intel_iommu
> *iommu,
>  			     struct iommu_gpasid_bind_data_vtd *pasid_data,
>  			     struct dmar_domain *domain, int addr_width);
>  void intel_pasid_tear_down_entry(struct intel_iommu *iommu,
> -				 struct device *dev, int pasid);
> +				 struct device *dev, int pasid, bool pf_ignore);
>  int vcmd_alloc_pasid(struct intel_iommu *iommu, unsigned int *pasid);
>  void vcmd_free_pasid(struct intel_iommu *iommu, unsigned int pasid);
>  #endif /* __INTEL_PASID_H */
> diff --git a/drivers/iommu/intel-svm.c b/drivers/iommu/intel-svm.c
> index 83dc4319f661..9561ba59a170 100644
> --- a/drivers/iommu/intel-svm.c
> +++ b/drivers/iommu/intel-svm.c
> @@ -207,7 +207,8 @@ static void intel_mm_release(struct mmu_notifier
> *mn, struct mm_struct *mm)
>  	 */
>  	rcu_read_lock();
>  	list_for_each_entry_rcu(sdev, &svm->devs, list) {
> -		intel_pasid_tear_down_entry(svm->iommu, sdev->dev, svm-
> >pasid);
> +		intel_pasid_tear_down_entry(svm->iommu, sdev->dev,
> +					    svm->pasid, true);
>  		intel_flush_svm_range_dev(svm, sdev, 0, -1, 0);
>  	}
>  	rcu_read_unlock();
> @@ -400,7 +401,8 @@ int intel_svm_unbind_gpasid(struct device *dev, int
> pasid)
>  		sdev->users--;
>  		if (!sdev->users) {
>  			list_del_rcu(&sdev->list);
> -			intel_pasid_tear_down_entry(iommu, dev, svm-
> >pasid);
> +			intel_pasid_tear_down_entry(iommu, dev,
> +						    svm->pasid, false);
>  			intel_flush_svm_range_dev(svm, sdev, 0, -1, 0);
>  			/* TODO: Drain in flight PRQ for the PASID since it
>  			 * may get reused soon, we don't want to
> @@ -643,7 +645,8 @@ int intel_svm_unbind_mm(struct device *dev, int
> pasid)
>  			 * to use. We have a *shared* PASID table, because
> it's
>  			 * large and has to be physically contiguous. So it's
>  			 * hard to be as defensive as we might like. */
> -			intel_pasid_tear_down_entry(iommu, dev, svm-
> >pasid);
> +			intel_pasid_tear_down_entry(iommu, dev,
> +						    svm->pasid, false);
>  			intel_flush_svm_range_dev(svm, sdev, 0, -1, 0);
>  			kfree_rcu(sdev, rcu);
> 
> --
> 2.17.1

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