linux-kernel - [PATCH 5.8 352/633] RDMA/umem: Fix ib_umem_find_best_pgsz() for mappings that cross a page boundary

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Date:   Tue, 27 Oct 2020 14:51:35 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Leon Romanovsky <leonro@...dia.com>,
        Shiraz Saleem <shiraz.saleem@...el.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.8 352/633] RDMA/umem: Fix ib_umem_find_best_pgsz() for mappings that cross a page boundary

From: Jason Gunthorpe <jgg@...dia.com>

[ Upstream commit a40c20dabdf9045270767c75918feb67f0727c89 ]

It is possible for a single SGL to span an aligned boundary, eg if the SGL
is

  61440 -> 90112

Then the length is 28672, which currently limits the block size to
32k. With a 32k page size the two covering blocks will be:

  32768->65536 and 65536->98304

However, the correct answer is a 128K block size which will span the whole
28672 bytes in a single block.

Instead of limiting based on length figure out which high IOVA bits don't
change between the start and end addresses. That is the highest useful
page size.

Fixes: 4a35339958f1 ("RDMA/umem: Add API to find best driver supported page size in an MR")
Link: https://lore.kernel.org/r/1-v2-270386b7e60b+28f4-umem_1_jgg@nvidia.com
Reviewed-by: Leon Romanovsky <leonro@...dia.com>
Reviewed-by: Shiraz Saleem <shiraz.saleem@...el.com>
Signed-off-by: Jason Gunthorpe <jgg@...dia.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/infiniband/core/umem.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
index 82455a1392f1d..1173b8cbe92b5 100644
--- a/drivers/infiniband/core/umem.c
+++ b/drivers/infiniband/core/umem.c
@@ -156,8 +156,13 @@ unsigned long ib_umem_find_best_pgsz(struct ib_umem *umem,
 		return 0;
 
 	va = virt;
-	/* max page size not to exceed MR length */
-	mask = roundup_pow_of_two(umem->length);
+	/* The best result is the smallest page size that results in the minimum
+	 * number of required pages. Compute the largest page size that could
+	 * work based on VA address bits that don't change.
+	 */
+	mask = pgsz_bitmap &
+	       GENMASK(BITS_PER_LONG - 1,
+		       bits_per((umem->length - 1 + virt) ^ virt));
 	/* offset into first SGL */
 	pgoff = umem->address & ~PAGE_MASK;
 
-- 
2.25.1