Re: [PATCH v5 4/7] iommu/sva: Stop using ioasid_set for SVA

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On 3/10/23 6:21 AM, 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>
---
v5:
	- Put removing iommu_sva_find() to a separate patch (Kevin)
	- Make pasid allocation range to be inclusive (Tina)
	- Simplified return code handling (Baolu)
v4:
	- Keep GFP_ATOMIC flag for PASID allocation, will changed to
	GFP_KERNEL in a separate patch.
---
  drivers/iommu/iommu-sva.c | 42 +++++++++++++--------------------------
  drivers/iommu/iommu-sva.h |  2 --
  2 files changed, 14 insertions(+), 30 deletions(-)

diff --git a/drivers/iommu/iommu-sva.c b/drivers/iommu/iommu-sva.c
index 4f357ef14f04..b75711bdbe97 100644
--- a/drivers/iommu/iommu-sva.c
+++ b/drivers/iommu/iommu-sva.c
@@ -9,47 +9,33 @@
  #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;
- if (min == INVALID_IOASID || max == INVALID_IOASID ||
-	    min == 0 || max < min)
+	if (!pasid_valid(min) || !pasid_valid(max) ||
+	     min == 0 || max < min)

No need to change above line.

  		return -EINVAL;
mutex_lock(&iommu_sva_lock);
  	/* Is a PASID already associated with this mm? */
  	if (pasid_valid(mm->pasid)) {
-		if (mm->pasid < min || mm->pasid >= max)
+		if (mm->pasid < min || mm->pasid > max)

I forgot why do we need to change above line. But it's better to put
some comments there so that people don't need to dive into
ioasid_alloc() to know the inclusion or exclusion of @min or @max.

  			ret = -EOVERFLOW;
  		goto out;
  	}
- pasid = ioasid_alloc(&iommu_sva_pasid, min, max, mm);
-	if (!pasid_valid(pasid))
-		ret = -ENOMEM;
-	else
-		mm->pasid = pasid;
+	ret = ida_alloc_range(&iommu_global_pasid_ida, min, max, GFP_ATOMIC);
+	if (ret < 0)
+		goto out;
+	mm->pasid = ret;
+	ret = 0;
  out:
  	mutex_unlock(&iommu_sva_lock);
  	return ret;
  }
-EXPORT_SYMBOL_GPL(iommu_sva_alloc_pasid);
/**
   * iommu_sva_bind_device() - Bind a process address space to a device
@@ -221,8 +207,8 @@ 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)))
+		return;
+
+	ida_free(&iommu_global_pasid_ida, mm->pasid);

Any reason why do you drop "mm->pasid = INVALID_IOASID;" here?

  }
diff --git a/drivers/iommu/iommu-sva.h b/drivers/iommu/iommu-sva.h
index 102eae1817a2..c22d0174ad61 100644
--- a/drivers/iommu/iommu-sva.h
+++ b/drivers/iommu/iommu-sva.h
@@ -8,8 +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);
-
  /* I/O Page fault */
  struct device;
  struct iommu_fault;

Best regards,
baolu



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