Fix lstopo

Lstopo doesn't have system memory mappings at low addresses. Make
sure we leave enough GPUVM address space for kernel allocations
(currently only CWSR) before the start of the user-managed SVM
aperture.

Change-Id: Ic197f7bd5a3cfb150a0da2bfdbc848664e7869be

src/fmm.c

@@ -1787,6 +1787,9 @@ err:
 	return ret;
 }
 
+#define DGPU_APERTURE_ADDR_MIN 0x1000000 /* Leave at least 16MB for kernel */
+#define DGPU_APERTURE_ADDR_INC 0x200000	 /* Search in huge-page increments */
+
 static HSAKMT_STATUS dgpu_mem_init(uint32_t gpu_mem_id, void **base, void **limit)
 {
 	bool found;
@@ -1815,9 +1818,9 @@ static HSAKMT_STATUS dgpu_mem_init(uint32_t gpu_mem_id, void **base, void **limi
 	found = false;
 
 	for (len = max_vm_limit+1; !found && len >= min_vm_size; len >>= 1) {
-		for (addr = (void *)TONGA_PAGE_SIZE, ret_addr = NULL;
+		for (addr = (void *)DGPU_APERTURE_ADDR_MIN, ret_addr = NULL;
 		     (HSAuint64)addr + (len >> 1) < max_vm_limit;
-		     addr = (void *)((HSAuint64)addr + TONGA_PAGE_SIZE)) {
+		     addr = (void *)((HSAuint64)addr + DGPU_APERTURE_ADDR_INC)) {
 			ret_addr = reserve_address(addr, len);
 			if (!ret_addr)
 				break;