From: Yong Zhao <yong.zhao@amd.com>
Date: Wed, 20 Sep 2017 18:10:21 -0400
Subject: drm/amdkfd: Fix kernel-queue wrapping bugs
Git-commit: cb1d9967461cdf3b6aac6317c8d954a14f842571
Patch-mainline: v4.14-rc3
References: FATE#326289 FATE#326079 FATE#326049 FATE#322398 FATE#326166

Avoid intermediate negative numbers when doing calculations with a mix
of signed and unsigned variables where implicit conversions can lead
to unexpected results.

When kernel queue buffer wraps around to 0, we need to check that rptr
won't be overwritten by the new packet.

Signed-off-by: Yong Zhao <yong.zhao@amd.com>
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>
Acked-by: Petr Tesarik <ptesarik@suse.com>
---
 drivers/gpu/drm/amd/amdkfd/kfd_kernel_queue.c |   18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

--- a/drivers/gpu/drm/amd/amdkfd/kfd_kernel_queue.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_kernel_queue.c
@@ -210,6 +210,11 @@ static int acquire_packet_buffer(struct
 	uint32_t wptr, rptr;
 	unsigned int *queue_address;
 
+	/* When rptr == wptr, the buffer is empty.
+	 * When rptr == wptr + 1, the buffer is full.
+	 * It is always rptr that advances to the position of wptr, rather than
+	 * the opposite. So we can only use up to queue_size_dwords - 1 dwords.
+	 */
 	rptr = *kq->rptr_kernel;
 	wptr = *kq->wptr_kernel;
 	queue_address = (unsigned int *)kq->pq_kernel_addr;
@@ -219,11 +224,10 @@ static int acquire_packet_buffer(struct
 	pr_debug("wptr: %d\n", wptr);
 	pr_debug("queue_address 0x%p\n", queue_address);
 
-	available_size = (rptr - 1 - wptr + queue_size_dwords) %
+	available_size = (rptr + queue_size_dwords - 1 - wptr) %
 							queue_size_dwords;
 
-	if (packet_size_in_dwords >= queue_size_dwords ||
-			packet_size_in_dwords >= available_size) {
+	if (packet_size_in_dwords > available_size) {
 		/*
 		 * make sure calling functions know
 		 * acquire_packet_buffer() failed
@@ -233,6 +237,14 @@ static int acquire_packet_buffer(struct
 	}
 
 	if (wptr + packet_size_in_dwords >= queue_size_dwords) {
+		/* make sure after rolling back to position 0, there is
+		 * still enough space.
+		 */
+		if (packet_size_in_dwords >= rptr) {
+			*buffer_ptr = NULL;
+			return -ENOMEM;
+		}
+		/* fill nops, roll back and start at position 0 */
 		while (wptr > 0) {
 			queue_address[wptr] = kq->nop_packet;
 			wptr = (wptr + 1) % queue_size_dwords;