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From:   Klaus Jensen <its@irrelevant.dk>
To:     linux-nvme@lists.infradead.org
Cc:     Christoph Hellwig <hch@lst.de>, Keith Busch <kbusch@kernel.org>,
        Jens Axboe <axboe@fb.com>, Sagi Grimberg <sagi@grimberg.me>,
        linux-kernel@vger.kernel.org, Klaus Jensen <its@irrelevant.dk>,
        Klaus Jensen <k.jensen@samsung.com>,
        Guenter Roeck <linux@roeck-us.net>
Subject: [PATCH] nvme-pci: fix doorbell buffer value endianness
Date:   Mon, 12 Dec 2022 16:02:43 +0100
Message-Id: <20221212150243.41283-1-its@irrelevant.dk>
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From: Klaus Jensen <k.jensen@samsung.com>

When using shadow doorbells, the event index and the doorbell values are
written to host memory. Prior to this patch, the values written would
erroneously be written in host endianness. This causes trouble on
big-endian platforms. Fix this by adding missing endian conversions.

This issue was noticed by Guenter while testing various big-endian
platforms under QEMU[1]. A similar fix required for hw/nvme in QEMU is
up for review as well[2].

  [1]: https://lore.kernel.org/qemu-devel/20221209110022.GA3396194@roeck-us.net/
  [2]: https://lore.kernel.org/qemu-devel/20221212114409.34972-4-its@irrelevant.dk/

Fixes: f9f38e33389c ("nvme: improve performance for virtual NVMe devices")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
---
 drivers/nvme/host/pci.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index f005e8569266..d12d4c3cb6d0 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -347,7 +347,7 @@ static bool nvme_dbbuf_update_and_check_event(u16 value, u32 *dbbuf_db,
 					      volatile u32 *dbbuf_ei)
 {
 	if (dbbuf_db) {
-		u16 old_value;
+		u16 old_value, event_idx;
 
 		/*
 		 * Ensure that the queue is written before updating
@@ -355,8 +355,8 @@ static bool nvme_dbbuf_update_and_check_event(u16 value, u32 *dbbuf_db,
 		 */
 		wmb();
 
-		old_value = *dbbuf_db;
-		*dbbuf_db = value;
+		old_value = le32_to_cpu(*dbbuf_db);
+		*dbbuf_db = cpu_to_le32(value);
 
 		/*
 		 * Ensure that the doorbell is updated before reading the event
@@ -366,7 +366,9 @@ static bool nvme_dbbuf_update_and_check_event(u16 value, u32 *dbbuf_db,
 		 */
 		mb();
 
-		if (!nvme_dbbuf_need_event(*dbbuf_ei, value, old_value))
+		event_idx = le32_to_cpu(*dbbuf_ei);
+
+		if (!nvme_dbbuf_need_event(event_idx, value, old_value))
 			return false;
 	}
 
-- 
2.38.1