[RFC PATCH 1/6] iommu/io-pgtable: Introduce unmap_pages() as a page table op

[Will Deacon]

From: "Isaac J. Manjarres" <isaacm at codeaurora.org>

The io-pgtable code expects to operate on a single block or
granule of memory that is supported by the IOMMU hardware when
unmapping memory.

This means that when a large buffer that consists of multiple
such blocks is unmapped, the io-pgtable code will walk the page
tables to the correct level to unmap each block, even for blocks
that are virtually contiguous and at the same level, which can
incur an overhead in performance.

Introduce the unmap_pages() page table op to express to the
io-pgtable code that it should unmap a number of blocks of
the same size, instead of a single block. Doing so allows
multiple blocks to be unmapped in one call to the io-pgtable
code, reducing the number of page table walks, and indirect
calls.

Signed-off-by: Isaac J. Manjarres <isaacm at codeaurora.org>
Suggested-by: Will Deacon <will at kernel.org>
Signed-off-by: Will Deacon <will at kernel.org>
---
 include/linux/io-pgtable.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/linux/io-pgtable.h b/include/linux/io-pgtable.h
index a4c9ca2c31f1..2ed0c057d9e7 100644
--- a/include/linux/io-pgtable.h
+++ b/include/linux/io-pgtable.h
@@ -144,6 +144,7 @@ struct io_pgtable_cfg {
  *
  * @map:          Map a physically contiguous memory region.
  * @unmap:        Unmap a physically contiguous memory region.
+ * @unmap_pages:  Unmap a range of virtually contiguous pages of the same size.
  * @iova_to_phys: Translate iova to physical address.
  *
  * These functions map directly onto the iommu_ops member functions with
@@ -154,6 +155,9 @@ struct io_pgtable_ops {
 		   phys_addr_t paddr, size_t size, int prot, gfp_t gfp);
 	size_t (*unmap)(struct io_pgtable_ops *ops, unsigned long iova,
 			size_t size, struct iommu_iotlb_gather *gather);
+	size_t (*unmap_pages)(struct io_pgtable_ops *ops, unsigned long iova,
+			      size_t pgsize, size_t pgcount,
+			      struct iommu_iotlb_gather *gather);
 	phys_addr_t (*iova_to_phys)(struct io_pgtable_ops *ops,
 				    unsigned long iova);
 };
-- 
2.31.0.291.g576ba9dcdaf-goog