iommu/sva: Assign a PASID to mm on PASID allocation and free it on mm exit

PASIDs are process-wide. It was attempted to use refcounted PASIDs to
free them when the last thread drops the refcount. This turned out to
be complex and error prone. Given the fact that the PASID space is 20
bits, which allows up to 1M processes to have a PASID associated
concurrently, PASID resource exhaustion is not a realistic concern.

Therefore, it was decided to simplify the approach and stick with lazy
on demand PASID allocation, but drop the eager free approach and make an
allocated PASID's lifetime bound to the lifetime of the process.

Get rid of the refcounting mechanisms and replace/rename the interfaces
to reflect this new approach.

  [ bp: Massage commit message. ]

Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Joerg Roedel <jroedel@suse.de>
Link: https://lore.kernel.org/r/20220207230254.3342514-6-fenghua.yu@intel.com

1 files changed, 0 insertions, 9 deletions

diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
index 5b5d69b04fcc..51ac2096b3da 100644
--- a/drivers/iommu/intel/svm.c
+++ b/drivers/iommu/intel/svm.c
@@ -514,11 +514,6 @@ static int intel_svm_alloc_pasid(struct device *dev, struct mm_struct *mm,
 	return iommu_sva_alloc_pasid(mm, PASID_MIN, max_pasid - 1);
 }
 
-static void intel_svm_free_pasid(struct mm_struct *mm)
-{
-	iommu_sva_free_pasid(mm);
-}
-
 static struct iommu_sva *intel_svm_bind_mm(struct intel_iommu *iommu,
 					   struct device *dev,
 					   struct mm_struct *mm,
@@ -662,8 +657,6 @@ static int intel_svm_unbind_mm(struct device *dev, u32 pasid)
 				kfree(svm);
 			}
 		}
-		/* Drop a PASID reference and free it if no reference. */
-		intel_svm_free_pasid(mm);
 	}
 out:
 	return ret;
@@ -1047,8 +1040,6 @@ struct iommu_sva *intel_svm_bind(struct device *dev, struct mm_struct *mm, void
 	}
 
 	sva = intel_svm_bind_mm(iommu, dev, mm, flags);
-	if (IS_ERR_OR_NULL(sva))
-		intel_svm_free_pasid(mm);
 	mutex_unlock(&pasid_mutex);
 
 	return sva;