From: Linus Walleij <linusw@kernel.org>
Date: Tue, 24 Feb 2026 10:26:32 +0000 (+0100)
Subject: fork: zero vmap stack using clear_pages() instead of memset()
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=929cc1a53a6f5a09e78451ba359e870727751f9e;p=thirdparty%2Flinux.git

fork: zero vmap stack using clear_pages() instead of memset()

After the introduction of clear_pages() we exploit the fact that the
process vm_area is allocated in contiguous pages to just clear them all in
one swift operation.

Link: https://lkml.kernel.org/r/20260224-mm-fork-clear-pages-v1-1-184c65a72d49@kernel.org
Signed-off-by: Linus Walleij <linusw@kernel.org>
Suggested-by: Mateusz Guzik <mjguzik@gmail.com>
Link: https://lore.kernel.org/linux-mm/dpnwsp7dl4535rd7qmszanw6u5an2p74uxfex4dh53frpb7pu3@2bnjjavjrepe/
Suggested-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Link: https://lore.kernel.org/20240311164638.2015063-7-pasha.tatashin@soleen.com
Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Ankur Arora <ankur.a.arora@oracle.com>
Cc: Ben Segall <bsegall@google.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/kernel/fork.c b/kernel/fork.c
index 1e80d4cdf5383..7fe5ab7d4ec61 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -345,7 +345,7 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node)
 		stack = kasan_reset_tag(vm_area->addr);
 
 		/* Clear stale pointers from reused stack. */
-		memset(stack, 0, THREAD_SIZE);
+		clear_pages(vm_area->addr, vm_area->nr_pages);
 
 		tsk->stack_vm_area = vm_area;
 		tsk->stack = stack;