nvme: Fix get/set number of queues feature, again]

Comments?

----- Forwarded message from Dan Aloni <[email protected]> -----

Date: Sun, 28 May 2017 16:06:49 +0300
From: Dan Aloni <[email protected]>
To: [email protected]
Cc: Alex Friedman <[email protected]>, Keith Busch <[email protected]>, Stefan Hajnoczi <[email protected]>
Subject: [PATCH] nvme: Fix get/set number of queues feature, again
X-Mailer: git-send-email 2.9.4

The number of queues that should be return by the admin command should:

1) Only mention the number of non-admin queues.
2) It is zero-based, meaning that '0 == one non-admin queue',

     '1 == two non-admin queues', and so forth.

Because our num_queues means the number of queues _plus_ the admin queue, then the right calculation for the number returned from the admin command is num_queues - 2, combining the two requirements mentioned.

The issue was discovered by reducing num_queues from 64 to 8 and running a Linux VM with an SMP parameter larger than that (e.g. 22). It tries to utilize all queues, and therefore fails with an invalid queue number when trying to queue I/Os on the last queue.

---
 hw/block/nvme.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index 7428db9f0c91..08ddf3a39e2f 100644
@@ -573,7 +573,7 @@ static uint16_t nvme_get_feature(NvmeCtrl *n, NvmeCmd *cmd, NvmeRequest *req)
         result = blk_enable_write_cache(n->conf.blk);
         break;
     case NVME_NUMBER_OF_QUEUES:
-        result = cpu_to_le32((n->num_queues - 1) | ((n->num_queues - 1) << 16));
+        result = cpu_to_le32((n->num_queues - 2) | ((n->num_queues - 2) << 16));
         break;
     default:
         return NVME_INVALID_FIELD | NVME_DNR;

@@ -594,7 +594,7 @@ static uint16_t nvme_set_feature(NvmeCtrl *n, NvmeCmd *cmd, NvmeRequest *req)
         break;
     case NVME_NUMBER_OF_QUEUES:
         req->cqe.result =
-            cpu_to_le32((n->num_queues - 1) | ((n->num_queues - 1) << 16));
+            cpu_to_le32((n->num_queues - 2) | ((n->num_queues - 2) << 16));
         break;
     default:
         return NVME_INVALID_FIELD | NVME_DNR;

2.9.4


----- End forwarded message -----

-- 
Dan Aloni