[PATCH mm] mm, kasan: fix for "integrate page_alloc init with HW_TAGS"

[Andrey Konovalov]

My commit "integrate page_alloc init with HW_TAGS" changed the order of
kernel_unpoison_pages() and kernel_init_free_pages() calls. This leads
to __GFP_ZERO allocations being incorrectly poisoned when page poisoning
is enabled.

Fix by restoring the initial order. Also add a warning comment.

Reported-by: Vlastimil Babka <vba...@suse.cz>
Reported-by: Sergei Trofimovich <sly...@gentoo.org>
Signed-off-by: Andrey Konovalov <andreyk...@google.com>
---
 mm/page_alloc.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 033bd92e8398..1fc5061f8ca1 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2328,6 +2328,12 @@ inline void post_alloc_hook(struct page *page, unsigned 
int order,
        arch_alloc_page(page, order);
        debug_pagealloc_map_pages(page, 1 << order);
 
+       /*
+        * Page unpoisoning must happen before memory initialization.
+        * Otherwise, a __GFP_ZERO allocation will not be initialized.
+        */
+       kernel_unpoison_pages(page, 1 << order);
+
        /*
         * As memory initialization might be integrated into KASAN,
         * kasan_alloc_pages and kernel_init_free_pages must be
@@ -2338,7 +2344,6 @@ inline void post_alloc_hook(struct page *page, unsigned 
int order,
        if (init && !kasan_has_integrated_init())
                kernel_init_free_pages(page, 1 << order);
 
-       kernel_unpoison_pages(page, 1 << order);
        set_page_owner(page, order, gfp_flags);
 }
 
-- 
2.31.0.291.g576ba9dcdaf-goog