Re: [PATCH 2/2] Revert "vmalloc: replace VM_NO_HUGE_VMAP with VM_ALLOW_HUGE_VMAP"

[Linus Torvalds <torvalds@linux-foundation.org>]

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On Fri, Apr 22, 2022 at 10:08 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> Just opt-in with the mappings that matter.

Actually, we could automatically opt-in a few common cases that we
know are fundamentally ok, because they already can't play protection
games.

In particular, kvmalloc().

So I think something like this patch - along with Song's patch to
enable it for alloc_large_system_hash() - would be fairly safe, and
avoid any nasty cases.

And probably catch quite a lot of the cases that matter that can grow large.

               Linus

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 mm/util.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/mm/util.c b/mm/util.c
index 54e5e761a9a9..3492a9e81aa3 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -592,8 +592,15 @@ void *kvmalloc_node(size_t size, gfp_t flags, int node)
 		return NULL;
 	}
 
-	return __vmalloc_node(size, 1, flags, node,
-			__builtin_return_address(0));
+	/*
+	 * kvmalloc() can always use VM_ALLOW_HUGE_VMAP,
+	 * since the callers already cannot assume anything
+	 * about the resulting pointer, and cannot play
+	 * protection games.
+	 */
+	return __vmalloc_node_range(size, 1, VMALLOC_START, VMALLOC_END,
+			flags, PAGE_KERNEL, VM_ALLOW_HUGE_VMAP,
+			node, __builtin_return_address(0));
 }
 EXPORT_SYMBOL(kvmalloc_node);