Re: [PATCH v4 3/6] iommu/sva: Stop using ioasid_set for SVA

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On 2023/3/2 7:56, Jacob Pan wrote:
From: Jason Gunthorpe <jgg@xxxxxxxxxx>

Instead SVA drivers can use a simple global IDA to allocate PASIDs for
each mm_struct.

Future work would be to allow drivers using the SVA APIs to reserve global
PASIDs from this IDA for their internal use, eg with the DMA API PASID
support.

Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
---
v4:
	- Keep GFP_ATOMIC flag for PASID allocation, will changed to
	GFP_KERNEL in a separate patch.
---
  drivers/iommu/iommu-sva.c | 62 ++++++++++-----------------------------
  drivers/iommu/iommu-sva.h |  3 --
  2 files changed, 15 insertions(+), 50 deletions(-)

diff --git a/drivers/iommu/iommu-sva.c b/drivers/iommu/iommu-sva.c
index 376b2a9e2543..297852ae5e7c 100644
--- a/drivers/iommu/iommu-sva.c
+++ b/drivers/iommu/iommu-sva.c
@@ -9,26 +9,13 @@
  #include "iommu-sva.h"
static DEFINE_MUTEX(iommu_sva_lock);
-static DECLARE_IOASID_SET(iommu_sva_pasid);
+static DEFINE_IDA(iommu_global_pasid_ida);
-/**
- * iommu_sva_alloc_pasid - Allocate a PASID for the mm
- * @mm: the mm
- * @min: minimum PASID value (inclusive)
- * @max: maximum PASID value (inclusive)
- *
- * Try to allocate a PASID for this mm, or take a reference to the existing one
- * provided it fits within the [@min, @max] range. On success the PASID is
- * available in mm->pasid and will be available for the lifetime of the mm.
- *
- * Returns 0 on success and < 0 on error.
- */
-int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t min, ioasid_t max)
+static int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t min, ioasid_t max)
  {
-	int ret = 0;
-	ioasid_t pasid;
+	int ret;
- if (min == INVALID_IOASID || max == INVALID_IOASID ||
+	if (min == IOMMU_PASID_INVALID || max == IOMMU_PASID_INVALID ||
  	    min == 0 || max < min)

It's irrelevant to this patch. Just out of curiosity, why do we need to
exclude PASID 0 here? I just had a quick look at PCI spec section 6.20.
The spec does not state that PASID 0 is invalid.

  		return -EINVAL;
@@ -37,39 +24,20 @@ int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t min, ioasid_t max)
  	if (pasid_valid(mm->pasid)) {
  		if (mm->pasid < min || mm->pasid >= max)
  			ret = -EOVERFLOW;
+		else
+			ret = 0;

Nit:

If you didn't change "int ret = 0" to "int ret", we don't need above two
lines. Did I miss anything?

  		goto out;
  	}
- pasid = ioasid_alloc(&iommu_sva_pasid, min, max, mm);
-	if (!pasid_valid(pasid))
-		ret = -ENOMEM;
-	else
-		mm->pasid = ret;
+	ret = ida_alloc_range(&iommu_global_pasid_ida, min, max, GFP_ATOMIC);
+	if (ret < min)

Nit:
	    ret < 0?

ida_alloc_range() returns negative error number on failure.

+		goto out;
+	mm->pasid = ret;
+	ret = 0;
  out:
  	mutex_unlock(&iommu_sva_lock);
  	return ret;
  }
-EXPORT_SYMBOL_GPL(iommu_sva_alloc_pasid);
-
-/* ioasid_find getter() requires a void * argument */
-static bool __mmget_not_zero(void *mm)
-{
-	return mmget_not_zero(mm);
-}
-
-/**
- * iommu_sva_find() - Find mm associated to the given PASID
- * @pasid: Process Address Space ID assigned to the mm
- *
- * On success a reference to the mm is taken, and must be released with mmput().
- *
- * Returns the mm corresponding to this PASID, or an error if not found.
- */
-struct mm_struct *iommu_sva_find(ioasid_t pasid)
-{
-	return ioasid_find(&iommu_sva_pasid, pasid, __mmget_not_zero);
-}
-EXPORT_SYMBOL_GPL(iommu_sva_find);

Removing iommu_sva_find() has nothing to do with the intention of this
patch. Perhaps make it in a separated patch?

/**
   * iommu_sva_bind_device() - Bind a process address space to a device
@@ -241,8 +209,8 @@ iommu_sva_handle_iopf(struct iommu_fault *fault, void *data)
void mm_pasid_drop(struct mm_struct *mm)
  {
-	if (pasid_valid(mm->pasid)) {
-		ioasid_free(mm->pasid);
-		mm->pasid = INVALID_IOASID;
-	}
+	if (likely(!pasid_valid(mm->pasid)))

Why is this a likely?

+		return;
+
+	ida_free(&iommu_global_pasid_ida, mm->pasid);
  }
diff --git a/drivers/iommu/iommu-sva.h b/drivers/iommu/iommu-sva.h
index 7215a761b962..c22d0174ad61 100644
--- a/drivers/iommu/iommu-sva.h
+++ b/drivers/iommu/iommu-sva.h
@@ -8,9 +8,6 @@
  #include <linux/ioasid.h>
  #include <linux/mm_types.h>
-int iommu_sva_alloc_pasid(struct mm_struct *mm, ioasid_t min, ioasid_t max);
-struct mm_struct *iommu_sva_find(ioasid_t pasid);
-
  /* I/O Page fault */
  struct device;
  struct iommu_fault;

Best regards,
baolu



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