linux-kernel - [PATCH 1/1] RDMA/mlx5: Fix page size bitmap calculation for KSM mode

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Message-ID: <20250824144839.154717-1-edwards@nvidia.com>
Date: Sun, 24 Aug 2025 17:48:39 +0300
From: Edward Srouji <edwards@...dia.com>
To: <edwards@...dia.com>, <jgg@...pe.ca>, <leon@...nel.org>
CC: <michaelgur@...dia.com>, <linux-rdma@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: [PATCH 1/1] RDMA/mlx5: Fix page size bitmap calculation for KSM mode

When using KSM (Key Scatter-gather Memory) access mode, the HW requires
the IOVA to be aligned to the selected page size.
Without this alignment, the HW may not function correctly.

Currently, mlx5_umem_mkc_find_best_pgsz() does not filter out page sizes
that would result in misaligned IOVAs for KSM mode. This can lead to
selecting page sizes that are incompatible with the given IOVA.

Fix this by filtering the page size bitmap when in KSM mode, keeping
only page sizes to which the IOVA is aligned to.

Fixes: fcfb03597b7d ("RDMA/mlx5: Align mkc page size capability check to PRM")
Signed-off-by: Edward Srouji <edwards@...dia.com>
Reviewed-by: Michael Guralnik <michaelgur@...dia.com>
---
 drivers/infiniband/hw/mlx5/mlx5_ib.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/infiniband/hw/mlx5/mlx5_ib.h b/drivers/infiniband/hw/mlx5/mlx5_ib.h
index 4fc2c0ca2af3..fbb9803785ba 100644
--- a/drivers/infiniband/hw/mlx5/mlx5_ib.h
+++ b/drivers/infiniband/hw/mlx5/mlx5_ib.h
@@ -1805,6 +1805,10 @@ mlx5_umem_mkc_find_best_pgsz(struct mlx5_ib_dev *dev, struct ib_umem *umem,
 
 	bitmap = GENMASK_ULL(max_log_entity_size_cap, min_log_entity_size_cap);
 
+	/* In KSM mode HW requires IOVA and mkey's page size to be aligned */
+	if (access_mode == MLX5_MKC_ACCESS_MODE_KSM && iova)
+		bitmap &= GENMASK_ULL(__ffs64(iova), 0);
+
 	return ib_umem_find_best_pgsz(umem, bitmap, iova);
 }
 
-- 
2.21.3