linux-kernel - [PATCH] mlx5: allow larger xsk chunk

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Date:   Wed, 13 Oct 2021 17:02:13 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Saeed Mahameed <saeedm@...dia.com>,
        Leon Romanovsky <leon@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tariq Toukan <tariqt@...dia.com>,
        Maxim Mikityanskiy <maximmi@...dia.com>,
        Aya Levin <ayal@...dia.com>,
        Eran Ben Elisha <eranbe@...dia.com>,
        Vladyslav Tarasiuk <vladyslavt@...dia.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: [PATCH] mlx5: allow larger xsk chunk_size

From: Arnd Bergmann <arnd@...db.de>

When building with 64KB pages, clang points out that xsk->chunk_size
can never be PAGE_SIZE:

drivers/net/ethernet/mellanox/mlx5/core/en/xsk/setup.c:19:22: error: result of comparison of constant 65536 with expression of type 'u16' (aka 'unsigned short') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
        if (xsk->chunk_size > PAGE_SIZE ||
            ~~~~~~~~~~~~~~~ ^ ~~~~~~~~~

I'm not familiar with the details of this code, but from a quick look
I found that it gets assigned from a 32-bit variable that can be
PAGE_SIZE, and that the layout of 'xsk' is not part of an ABI or
a hardware structure, so extending the members to 32 bits as well
should address both the behavior on 64KB page kernels, and the
warning I saw.

In older versions of this code, using PAGE_SIZE was the only
possibility, so this would have never worked on 64KB page kernels,
but the patch apparently did not address this case completely.

Fixes: 282c0c798f8e ("net/mlx5e: Allow XSK frames smaller than a page")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/net/ethernet/mellanox/mlx5/core/en/params.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/params.h b/drivers/net/ethernet/mellanox/mlx5/core/en/params.h
index 879ad46d754e..b4167350b6df 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en/params.h
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en/params.h
@@ -7,8 +7,8 @@
 #include "en.h"
 
 struct mlx5e_xsk_param {
-	u16 headroom;
-	u16 chunk_size;
+	u32 headroom;
+	u32 chunk_size;
 };
 
 struct mlx5e_lro_param {
-- 
2.29.2