Revert "mm: init_mlocked_on_free_v3"

There was insufficient review and no agreement that this is the right
approach.

There are serious flaws with the implementation that make processes using
mlock() not even work with simple fork() [1] and we get reliable crashes
when rebooting.

Further, simply because we might be unmapping a single PTE of a large
mlocked folio, we shouldn't zero out the whole folio.

... especially because the code can also *corrupt* urelated memory because
	kernel_init_pages(page, folio_nr_pages(folio));

Could end up writing outside of the actual folio if we work with a tail
page.

Let's revert it.  Once there is agreement that this is the right approach,
the issues were fixed and there was reasonable review and proper testing,
we can consider it again.

[1] https://lkml.kernel.org/r/4da9da2f-73e4-45fd-b62f-a8a513314057@redhat.com

Link: https://lkml.kernel.org/r/20240605091710.38961-1-david@redhat.com
Fixes: ba42b524a040 ("mm: init_mlocked_on_free_v3")
Signed-off-by: David Hildenbrand <david@redhat.com>
Reported-by: David Wang <00107082@163.com>
Closes: https://lore.kernel.org/lkml/20240528151340.4282-1-00107082@163.com/
Reported-by: Lance Yang <ioworker0@gmail.com>
Closes: https://lkml.kernel.org/r/20240601140917.43562-1-ioworker0@gmail.com
Acked-by: Lance Yang <ioworker0@gmail.com>
Cc: York Jasper Niebuhr <yjnworkstation@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 7 insertions, 36 deletions

diff --git a/mm/mm_init.c b/mm/mm_init.c
index f72b852bd5b8..3ec04933f7fd 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -2523,9 +2523,6 @@ EXPORT_SYMBOL(init_on_alloc);
 DEFINE_STATIC_KEY_MAYBE(CONFIG_INIT_ON_FREE_DEFAULT_ON, init_on_free);
 EXPORT_SYMBOL(init_on_free);
 
-DEFINE_STATIC_KEY_MAYBE(CONFIG_INIT_MLOCKED_ON_FREE_DEFAULT_ON, init_mlocked_on_free);
-EXPORT_SYMBOL(init_mlocked_on_free);
-
 static bool _init_on_alloc_enabled_early __read_mostly
 				= IS_ENABLED(CONFIG_INIT_ON_ALLOC_DEFAULT_ON);
 static int __init early_init_on_alloc(char *buf)
@@ -2543,14 +2540,6 @@ static int __init early_init_on_free(char *buf)
 }
 early_param("init_on_free", early_init_on_free);
 
-static bool _init_mlocked_on_free_enabled_early __read_mostly
-				= IS_ENABLED(CONFIG_INIT_MLOCKED_ON_FREE_DEFAULT_ON);
-static int __init early_init_mlocked_on_free(char *buf)
-{
-	return kstrtobool(buf, &_init_mlocked_on_free_enabled_early);
-}
-early_param("init_mlocked_on_free", early_init_mlocked_on_free);
-
 DEFINE_STATIC_KEY_MAYBE(CONFIG_DEBUG_VM, check_pages_enabled);
 
 /*
@@ -2578,21 +2567,12 @@ static void __init mem_debugging_and_hardening_init(void)
 	}
 #endif
 
-	if ((_init_on_alloc_enabled_early || _init_on_free_enabled_early ||
-	    _init_mlocked_on_free_enabled_early) &&
+	if ((_init_on_alloc_enabled_early || _init_on_free_enabled_early) &&
 	    page_poisoning_requested) {
 		pr_info("mem auto-init: CONFIG_PAGE_POISONING is on, "
-			"will take precedence over init_on_alloc, init_on_free "
-			"and init_mlocked_on_free\n");
+			"will take precedence over init_on_alloc and init_on_free\n");
 		_init_on_alloc_enabled_early = false;
 		_init_on_free_enabled_early = false;
-		_init_mlocked_on_free_enabled_early = false;
-	}
-
-	if (_init_mlocked_on_free_enabled_early && _init_on_free_enabled_early) {
-		pr_info("mem auto-init: init_on_free is on, "
-			"will take precedence over init_mlocked_on_free\n");
-		_init_mlocked_on_free_enabled_early = false;
 	}
 
 	if (_init_on_alloc_enabled_early) {
@@ -2609,17 +2589,9 @@ static void __init mem_debugging_and_hardening_init(void)
 		static_branch_disable(&init_on_free);
 	}
 
-	if (_init_mlocked_on_free_enabled_early) {
-		want_check_pages = true;
-		static_branch_enable(&init_mlocked_on_free);
-	} else {
-		static_branch_disable(&init_mlocked_on_free);
-	}
-
-	if (IS_ENABLED(CONFIG_KMSAN) && (_init_on_alloc_enabled_early ||
-	    _init_on_free_enabled_early || _init_mlocked_on_free_enabled_early))
-		pr_info("mem auto-init: please make sure init_on_alloc, init_on_free and "
-			"init_mlocked_on_free are disabled when running KMSAN\n");
+	if (IS_ENABLED(CONFIG_KMSAN) &&
+	    (_init_on_alloc_enabled_early || _init_on_free_enabled_early))
+		pr_info("mem auto-init: please make sure init_on_alloc and init_on_free are disabled when running KMSAN\n");
 
 #ifdef CONFIG_DEBUG_PAGEALLOC
 	if (debug_pagealloc_enabled()) {
@@ -2658,10 +2630,9 @@ static void __init report_meminit(void)
 	else
 		stack = "off";
 
-	pr_info("mem auto-init: stack:%s, heap alloc:%s, heap free:%s, mlocked free:%s\n",
+	pr_info("mem auto-init: stack:%s, heap alloc:%s, heap free:%s\n",
 		stack, want_init_on_alloc(GFP_KERNEL) ? "on" : "off",
-		want_init_on_free() ? "on" : "off",
-		want_init_mlocked_on_free() ? "on" : "off");
+		want_init_on_free() ? "on" : "off");
 	if (want_init_on_free())
 		pr_info("mem auto-init: clearing system memory may take some time...\n");
 }