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From: Bing Zhao <>
Subject: [dpdk-stable] [PATCH] net/mlx5: fix left shift extension of doorbell bitmap
Date: Fri, 15 May 2020 16:13:58 +0800
Message-ID: <> (raw)

The doorbell record is organized with page and bitmap. When some new
doorbell needs to be associated with a queue, the bit will be set
in the bitmap to indicate the corresponding doorbell occupied. A
counter is used to record the number of doorbell occupied to speed
up the searching.
If the number reachs the maximal value of a pre-defined number of a
page, a new page will be allocated. If not, then the bitmap will be
checked to find a free one.
The LSHIFT and OR (AND NOT) operations are used to update the bitmap
of a page. But 1 will be treated as a signed integer when compiling.
When the shift number is 31, the shifted value will be considered as
negative. Then a wrong extension will be done when setting it to a
64-bits variable. All the upper 32-bits will be set to 1 by such
Then a wrong offset value will be calculated because of this. The
next 64 bits will be also treated as the bitmap and get corrupted
through the bit set operation.
The immediate value 1 needs to be used as 64 bits width explicitly.

Fixes: 21cae8580fd0 ("net/mlx5: allocate door-bells via DevX")

Signed-off-by: Bing Zhao <>
Acked-by: Viacheslav Ovsiienko <>
 drivers/net/mlx5/mlx5.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/mlx5/mlx5.c b/drivers/net/mlx5/mlx5.c
index 1445809..ab4adec 100644
--- a/drivers/net/mlx5/mlx5.c
+++ b/drivers/net/mlx5/mlx5.c
@@ -2174,7 +2174,7 @@ struct mlx5_flow_id_pool *
 	/* Find the first clear bit. */
 	j = rte_bsf64(~page->dbr_bitmap[i]);
-	page->dbr_bitmap[i] |= (1 << j);
+	page->dbr_bitmap[i] |= (UINT64_C(1) << j);
 	*dbr_page = page;
 	return (((i * 64) + j) * sizeof(uint64_t));
@@ -2219,7 +2219,7 @@ struct mlx5_flow_id_pool *
 		int i = offset / 64;
 		int j = offset % 64;
-		page->dbr_bitmap[i] &= ~(1 << j);
+		page->dbr_bitmap[i] &= ~(UINT64_C(1) << j);
 	return ret;

             reply	other threads:[~2020-05-15  8:14 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-15  8:13 Bing Zhao [this message]
2020-05-17  5:45 ` Matan Azrad
2020-05-17  9:18 ` Raslan Darawsheh
2020-05-17  9:54   ` Raslan Darawsheh

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