Re: [PATCH v3 25/25] IB/mlx4: Workaround for mlx4_alloc_priv_pages() array allocator

Ensure the MR's PBL array never occupies the last 8 bytes of a page.
This eliminates random "Local Protection Error" flushes when SLUB
debugging is enabled.

Fixes: 1b2cd0fc673c ('IB/mlx4: Support the new memory registration API')
Suggested-by: Christoph Hellwig <redacted>
Signed-off-by: Chuck Lever <redacted>
---
  drivers/infiniband/hw/mlx4/mlx4_ib.h |    2 +-
  drivers/infiniband/hw/mlx4/mr.c      |   40 +++++++++++++++++++---------------
  2 files changed, 23 insertions(+), 19 deletions(-)

diff --git a/drivers/infiniband/hw/mlx4/mlx4_ib.h b/drivers/infiniband/hw/mlx4/mlx4_ib.h
index 6c5ac5d..29acda2 100644
--- a/drivers/infiniband/hw/mlx4/mlx4_ib.h
+++ b/drivers/infiniband/hw/mlx4/mlx4_ib.h

@@ -139,7 +139,7 @@ struct mlx4_ib_mr {
  	u32			max_pages;
  	struct mlx4_mr		mmr;
  	struct ib_umem	       *umem;
-	void			*pages_alloc;
+	size_t			page_map_size;
  };

  struct mlx4_ib_mw {

diff --git a/drivers/infiniband/hw/mlx4/mr.c b/drivers/infiniband/hw/mlx4/mr.c
index 6312721..b90e47c 100644
--- a/drivers/infiniband/hw/mlx4/mr.c
+++ b/drivers/infiniband/hw/mlx4/mr.c

@@ -277,20 +277,27 @@ mlx4_alloc_priv_pages(struct ib_device *device,
  		      struct mlx4_ib_mr *mr,
  		      int max_pages)
  {
-	int size = max_pages * sizeof(u64);
-	int add_size;
  	int ret;

-	add_size = max_t(int, MLX4_MR_PAGES_ALIGN - ARCH_KMALLOC_MINALIGN, 0);
-
-	mr->pages_alloc = kzalloc(size + add_size, GFP_KERNEL);
-	if (!mr->pages_alloc)
+	/* Round mapping size up to ensure DMA cacheline
+	 * alignment, and cache the size to avoid mult/div
+	 * in fast path.
+	 */
+	mr->page_map_size = roundup(max_pages * sizeof(u64),
+				    MLX4_MR_PAGES_ALIGN);
+	if (mr->page_map_size > PAGE_SIZE)
+		return -EINVAL;
+
+	/* This is overkill, but hardware requires that the
+	 * PBL array begins at a properly aligned address and
+	 * never occupies the last 8 bytes of a page.
+	 */
+	mr->pages = (__be64 *)get_zeroed_page(GFP_KERNEL);
+	if (!mr->pages)
  		return -ENOMEM;