drm/ttm: Implement vm_operations_struct.access v2

Allows gdb to access contents of user mode mapped BOs. System memory
is handled by TTM using kmap. Other memory pools require a new driver
callback in ttm_bo_driver.

v2:
* kmap only one page at a time
* swap in BO if needed
* make driver callback more generic to handle private memory pools
* document callback return value
* WARN_ON -> WARN_ON_ONCE

Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/ttm/ttm_bo_vm.c

@@ -294,10 +294,87 @@ static void ttm_bo_vm_close(struct vm_area_struct *vma)
 	vma->vm_private_data = NULL;
 }
 
+static int ttm_bo_vm_access_kmap(struct ttm_buffer_object *bo,
+				 unsigned long offset,
+				 void *buf, int len, int write)
+{
+	unsigned long page = offset >> PAGE_SHIFT;
+	unsigned long bytes_left = len;
+	int ret;
+
+	/* Copy a page at a time, that way no extra virtual address
+	 * mapping is needed
+	 */
+	offset -= page << PAGE_SHIFT;
+	do {
+		unsigned long bytes = min(bytes_left, PAGE_SIZE - offset);
+		struct ttm_bo_kmap_obj map;
+		void *ptr;
+		bool is_iomem;
+
+		ret = ttm_bo_kmap(bo, page, 1, &map);
+		if (ret)
+			return ret;
+
+		ptr = (uint8_t *)ttm_kmap_obj_virtual(&map, &is_iomem) + offset;
+		WARN_ON_ONCE(is_iomem);
+		if (write)
+			memcpy(ptr, buf, bytes);
+		else
+			memcpy(buf, ptr, bytes);
+		ttm_bo_kunmap(&map);
+
+		page++;
+		bytes_left -= bytes;
+		offset = 0;
+	} while (bytes_left);
+
+	return len;
+}
+
+static int ttm_bo_vm_access(struct vm_area_struct *vma, unsigned long addr,
+			    void *buf, int len, int write)
+{
+	unsigned long offset = (addr) - vma->vm_start;
+	struct ttm_buffer_object *bo = vma->vm_private_data;
+	int ret;
+
+	if (len < 1 || (offset + len) >> PAGE_SHIFT > bo->num_pages)
+		return -EIO;
+
+	ret = ttm_bo_reserve(bo, true, false, NULL);
+	if (ret)
+		return ret;
+
+	switch (bo->mem.mem_type) {
+	case TTM_PL_SYSTEM:
+		if (unlikely(bo->ttm->page_flags & TTM_PAGE_FLAG_SWAPPED)) {
+			ret = ttm_tt_swapin(bo->ttm);
+			if (unlikely(ret != 0))
+				return ret;
+		}
+		/* fall through */
+	case TTM_PL_TT:
+		ret = ttm_bo_vm_access_kmap(bo, offset, buf, len, write);
+		break;
+	default:
+		if (bo->bdev->driver->access_memory)
+			ret = bo->bdev->driver->access_memory(
+				bo, offset, buf, len, write);
+		else
+			ret = -EIO;
+	}
+
+	ttm_bo_unreserve(bo);
+
+	return ret;
+}
+
 static const struct vm_operations_struct ttm_bo_vm_ops = {
 	.fault = ttm_bo_vm_fault,
 	.open = ttm_bo_vm_open,
-	.close = ttm_bo_vm_close
+	.close = ttm_bo_vm_close,
+	.access = ttm_bo_vm_access
 };
 
 static struct ttm_buffer_object *ttm_bo_vm_lookup(struct ttm_bo_device *bdev,

include/drm/ttm/ttm_bo_driver.h

@@ -472,6 +472,23 @@ struct ttm_bo_driver {
 	 */
 	unsigned long (*io_mem_pfn)(struct ttm_buffer_object *bo,
 				    unsigned long page_offset);
+
+	/**
+	 * Read/write memory buffers for ptrace access
+	 *
+	 * @bo: the BO to access
+	 * @offset: the offset from the start of the BO
+	 * @buf: pointer to source/destination buffer
+	 * @len: number of bytes to copy
+	 * @write: whether to read (0) from or write (non-0) to BO
+	 *
+	 * If successful, this function should return the number of
+	 * bytes copied, -EIO otherwise. If the number of bytes
+	 * returned is < len, the function may be called again with
+	 * the remainder of the buffer to copy.
+	 */
+	int (*access_memory)(struct ttm_buffer_object *bo, unsigned long offset,
+			     void *buf, int len, int write);
 };
 
 /**