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FROMGIT: mm, page_poison: remove CONFIG_PAGE_POISONING_ZERO

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CONFIG_PAGE_POISONING_ZERO uses the zero pattern instead of 0xAA.  It was
introduced by commit 1414c7f4f7 ("mm/page_poisoning.c: allow for zero
poisoning"), noting that using zeroes retains the benefit of sanitizing
content of freed pages, with the benefit of not having to zero them again
on alloc, and the downside of making some forms of corruption (stray
writes of NULLs) harder to detect than with the 0xAA pattern.  Together
with CONFIG_PAGE_POISONING_NO_SANITY it made possible to sanitize the
contents on free without checking it back on alloc.

These days we have the init_on_free() option to achieve sanitization with
zeroes and to save clearing on alloc (and without checking on alloc).
Arguably if someone does choose to check the poison for corruption on
alloc, the savings of not clearing the page are secondary, and it makes
sense to always use the 0xAA poison pattern.  Thus, remove the
CONFIG_PAGE_POISONING_ZERO option for being redundant.

Link: https://lkml.kernel.org/r/20201113104033.22907-6-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Laura Abbott <labbott@kernel.org>
Cc: Mateusz Nosek <mateusznosek0@gmail.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

(cherry picked from commit f289041ed4cf9a3f6e8a32068fef9ffb2acc5662
 https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git akpm)
Bug: 182930667
Signed-off-by: Alexander Potapenko <glider@google.com>
Change-Id: I57e19d1dd77d3d5eec40f94c1b64a877c3710baa
This commit is contained in:
Vlastimil Babka
2020-12-14 19:13:45 -08:00
committed by Todd Kjos
parent ca96c45d7a
commit fa44968ac4
4 changed files with 2 additions and 28 deletions
Download Patch File Download Diff File Expand all files Collapse all files

8
mm/page_alloc.c
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@@ -2262,12 +2262,6 @@ static inline int check_new_page(struct page *page)
return 1;
}
static inline bool free_pages_prezeroed(void)
{
return (IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) &&
page_poisoning_enabled_static()) || want_init_on_free();
}
#ifdef CONFIG_DEBUG_VM
/*
* With DEBUG_VM enabled, order-0 pages are checked for expected state when
@@ -2331,7 +2325,7 @@ inline void post_alloc_hook(struct page *page, unsigned int order,
kernel_unpoison_pages(page, 1 << order);
set_page_owner(page, order, gfp_flags);
if (!free_pages_prezeroed() && want_init_on_alloc(gfp_flags))
if (!want_init_on_free() && want_init_on_alloc(gfp_flags))
kernel_init_free_pages(page, 1 << order);
}