linux-kernel - [PATCH 5.6 130/177] drm/amd/display: Fix potential integer wraparound resulting in a hang

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Date:   Mon,  1 Jun 2020 19:54:28 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Aric Cyr <aric.cyr@....com>,
        Nicholas Kazlauskas <Nicholas.Kazlauskas@....com>,
        Qingqing Zhuo <qingqing.zhuo@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.6 130/177] drm/amd/display: Fix potential integer wraparound resulting in a hang

From: Aric Cyr <aric.cyr@....com>

[ Upstream commit 4e5183200d9b66695c754ef214933402056e7b95 ]

[Why]
If VUPDATE_END is before VUPDATE_START the delay calculated can become
very large, causing a soft hang.

[How]
Take the absolute value of the difference between START and END.

Signed-off-by: Aric Cyr <aric.cyr@....com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@....com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@....com>
Signed-off-by: Alex Deucher <alexander.deucher@....com>
Cc: stable@...r.kernel.org
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c b/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c
index 60cea910759b..0c987b5d68e2 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c
+++ b/drivers/gpu/drm/amd/display/dc/dcn10/dcn10_hw_sequencer.c
@@ -1651,6 +1651,8 @@ static void delay_cursor_until_vupdate(struct dc *dc, struct pipe_ctx *pipe_ctx)
 		return;
 
 	/* Stall out until the cursor update completes. */
+	if (vupdate_end < vupdate_start)
+		vupdate_end += stream->timing.v_total;
 	us_vupdate = (vupdate_end - vupdate_start + 1) * us_per_line;
 	udelay(us_to_vupdate + us_vupdate);
 }
-- 
2.25.1