Re: [PATCH mm v2] mm, kasan: fix for "integrate page_alloc init with HW_TAGS"

[Vlastimil Babka]

On 3/30/21 6:37 PM, Andrey Konovalov wrote:
> 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 complaints from the page unpoisoning code, as the poison pattern gets
> overwritten for __GFP_ZERO allocations.
> 
> Fix by restoring the initial order. Also add a warning comment.
> 
> Reported-by: Vlastimil Babka <vbabka@xxxxxxx>
> Reported-by: Sergei Trofimovich <slyfox@xxxxxxxxxx>
> Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>

Tested that the bug indeed occurs in -next and is fixed by this. Thanks.

> ---
>  mm/page_alloc.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 033bd92e8398..d2c020563c0b 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2328,6 +2328,13 @@ 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, the poison pattern will be overwritten for __GFP_ZERO
> +	 * allocations and the page unpoisoning code will complain.
> +	 */
> +	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 +2345,6 @@ 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);
>  }
>  
>