dev-amdgpu: Writeback RLC queue MQD when unmapped

Currently when RLC queues (user mode queues) are mapped, the read/write
pointers of the ring buffer are set to zero. However, these queues could
be unmapped and then remapped later. In that situation the read/write
pointers should be the previous value before unmapping occurred. Since
the read pointer gets reset to zero, the queue begins reading from the
start of the ring, which usually contains older packets. There is a 99%
chance those packets contain addresses which are no longer in the page
tables which will cause a page fault.

To fix this we update the MQD with the current read/write pointer values
and then writeback the MQD to memory when the queue is unmapped. This
requires adding a pointer to the MQD and the host address of the MQD
where it should be written back to. The interface for registering RLC
queue is also simplified. Since we need to pass the MQD anyway, we can
get values from it as well.

Fixes b+tree and streamcluster from rodinia (when using RLC queues).

Change-Id: Ie5dad4d7d90ea240c3e9f0cddf3e844a3cd34c4f
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/65791
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Matt Sinclair <mattdsinclair@gmail.com>
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>

src/dev/amdgpu/pm4_packet_processor.cc

@@ -458,9 +458,7 @@ PM4PacketProcessor::processSDMAMQD(PM4MapQueues *pkt, PM4Queue *q, Addr addr,
     SDMAEngine *sdma_eng = gpuDevice->getSDMAById(pkt->engineSel - 2);
 
     // Register RLC queue with SDMA
-    sdma_eng->registerRLCQueue(pkt->doorbellOffset << 2,
-                               mqd->rb_base << 8, rlc_size,
-                               rptr_wb_addr);
+    sdma_eng->registerRLCQueue(pkt->doorbellOffset << 2, addr, mqd);
 
     // Register doorbell with GPU device
     gpuDevice->setSDMAEngine(pkt->doorbellOffset << 2, sdma_eng);