patch 'dma/idxd: fix wrap-around in burst capacity calculation' has been queued to stable release 21.11.1

[Kevin Traynor]

Hi,

FYI, your patch has been queued to stable release 21.11.1

Note it hasn't been pushed to http://dpdk.org/browse/dpdk-stable yet.
It will be pushed if I get no objections before 02/26/22. So please
shout if anyone has objections.

Also note that after the patch there's a diff of the upstream commit vs the
patch applied to the branch. This will indicate if there was any rebasing
needed to apply to the stable branch. If there were code changes for rebasing
(ie: not only metadata diffs), please double check that the rebase was
correctly done.

Queued patches are on a temporary branch at:
https://github.com/kevintraynor/dpdk-stable

This queued commit can be viewed at:
https://github.com/kevintraynor/dpdk-stable/commit/8e8fe373c0e8b4842d7e1dc4a382edc280f9a03a

Thanks.

Kevin

---
>From 8e8fe373c0e8b4842d7e1dc4a382edc280f9a03a Mon Sep 17 00:00:00 2001
From: Bruce Richardson <bruce.richardson at intel.com>
Date: Tue, 11 Jan 2022 13:41:04 +0000
Subject: [PATCH] dma/idxd: fix wrap-around in burst capacity calculation

[ upstream commit 63990aeb08f45f0acd435f67fd52a3736a493563 ]

The burst capacity calculation code assumes that the write and read
(i.e. ids_returned) values both wrap at the ring-size, but the read
value instead wraps as UINT16_MAX. Therefore, instead of just adding
ring-size to the write value in case the read is greater, we need to
just always mask the result to ensure a correct, in-range, value.

Fixes: 9459de4edc99 ("dma/idxd: add burst capacity")

Reported-by: Sunil Pai G <sunil.pai.g at intel.com>
Signed-off-by: Bruce Richardson <bruce.richardson at intel.com>
Tested-by: Sunil Pai G <sunil.pai.g at intel.com>
Acked-by: Kevin Laatz <kevin.laatz at intel.com>
---
 drivers/dma/idxd/idxd_common.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/dma/idxd/idxd_common.c b/drivers/dma/idxd/idxd_common.c
index 4442d1cbbd..ea6413cc7a 100644
--- a/drivers/dma/idxd/idxd_common.c
+++ b/drivers/dma/idxd/idxd_common.c
@@ -481,8 +481,6 @@ idxd_burst_capacity(const void *dev_private, uint16_t vchan __rte_unused)
 		return 0;
 
-	/* For descriptors, check for wrap-around on write but not read */
-	if (idxd->ids_returned > write_idx)
-		write_idx += idxd->desc_ring_mask + 1;
-	used_space = write_idx - idxd->ids_returned;
+	/* Subtract and mask to get in correct range */
+	used_space = (write_idx - idxd->ids_returned) & idxd->desc_ring_mask;
 
 	const int ret = RTE_MIN((idxd->desc_ring_mask - used_space),
-- 
2.34.1

---
  Diff of the applied patch vs upstream commit (please double-check if non-empty:
---
--- -	2022-02-21 15:22:44.889725852 +0000
+++ 0009-dma-idxd-fix-wrap-around-in-burst-capacity-calculati.patch	2022-02-21 15:22:44.036704001 +0000
@@ -1 +1 @@
-From 63990aeb08f45f0acd435f67fd52a3736a493563 Mon Sep 17 00:00:00 2001
+From 8e8fe373c0e8b4842d7e1dc4a382edc280f9a03a Mon Sep 17 00:00:00 2001
@@ -5,0 +6,2 @@
+[ upstream commit 63990aeb08f45f0acd435f67fd52a3736a493563 ]
+
@@ -13 +14,0 @@
-Cc: stable at dpdk.org