On Mon, Oct 26, 2020 at 01:13:52AM +0000, Edgecombe, Rick P wrote:

On Sun, 2020-10-25 at 12:15 +0200, Mike Rapoport wrote:

quoted

Indeed, for architectures that define CONFIG_ARCH_HAS_SET_DIRECT_MAP
it is
possible that __kernel_map_pages() would fail, but since this
function is
void, the failure will go unnoticed.

Could you elaborate on how this could happen? Do you mean during
runtime today or if something new was introduced?

A failure in__kernel_map_pages() may happen today. For instance, on x86
if the kernel is built with DEBUG_PAGEALLOC.

	__kernel_map_pages(page, 1, 0);

will need to split, say, 2M page and during the split an allocation of
page table could fail.

Currently, the only user of __kernel_map_pages() outside DEBUG_PAGEALLOC
is hibernation, but I think it would be safer to entirely prevent usage
of __kernel_map_pages() when DEBUG_PAGEALLOC=n.

-- 
Sincerely yours,
Mike.