linux-kernel - [PATCH v4 2/6] IB/mlx4: Eliminate duplicate barriers on weakly-ordered archs

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <1521514068-8856-3-git-send-email-okaya@codeaurora.org>
Date:   Mon, 19 Mar 2018 22:47:44 -0400
From:   Sinan Kaya <okaya@...eaurora.org>
To:     linux-rdma@...r.kernel.org, timur@...eaurora.org,
        sulrich@...eaurora.org
Cc:     linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Sinan Kaya <okaya@...eaurora.org>,
        Yishai Hadas <yishaih@...lanox.com>,
        Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>, linux-kernel@...r.kernel.org
Subject: [PATCH v4 2/6] IB/mlx4: Eliminate duplicate barriers on weakly-ordered archs

Code includes wmb() followed by writel(). writel() already has a barrier on
some architectures like arm64.

This ends up CPU observing two barriers back to back before executing the
register write.

Since code already has an explicit barrier call, changing writel() to
writel_relaxed().

Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
---
 drivers/infiniband/hw/mlx4/qp.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/infiniband/hw/mlx4/qp.c b/drivers/infiniband/hw/mlx4/qp.c
index f045491..74b27b0 100644
--- a/drivers/infiniband/hw/mlx4/qp.c
+++ b/drivers/infiniband/hw/mlx4/qp.c
@@ -3880,8 +3880,8 @@ int mlx4_ib_post_send(struct ib_qp *ibqp, struct ib_send_wr *wr,
 		 */
 		wmb();
 
-		writel(qp->doorbell_qpn,
-		       to_mdev(ibqp->device)->uar_map + MLX4_SEND_DOORBELL);
+		writel_relaxed(qp->doorbell_qpn,
+			to_mdev(ibqp->device)->uar_map + MLX4_SEND_DOORBELL);
 
 		/*
 		 * Make sure doorbells don't leak out of SQ spinlock
-- 
2.7.4