linux-kernel - Re: [PATCH 04/31] kasan, page_alloc: simplify kasan_poison

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Date:   Wed, 1 Dec 2021 15:09:56 +0100
From:   Marco Elver <elver@...gle.com>
To:     andrey.konovalov@...ux.dev
Cc:     Alexander Potapenko <glider@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Peter Collingbourne <pcc@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        kasan-dev@...glegroups.com,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Evgenii Stepanov <eugenis@...gle.com>,
        linux-kernel@...r.kernel.org,
        Andrey Konovalov <andreyknvl@...gle.com>
Subject: Re: [PATCH 04/31] kasan, page_alloc: simplify kasan_poison_pages
 call site

On Tue, Nov 30, 2021 at 10:39PM +0100, andrey.konovalov@...ux.dev wrote:
> From: Andrey Konovalov <andreyknvl@...gle.com>
> 
> Simplify the code around calling kasan_poison_pages() in
> free_pages_prepare().
> 
> Reording kasan_poison_pages() and kernel_init_free_pages() is OK,
> since kernel_init_free_pages() can handle poisoned memory.

Why did they have to be reordered?

> This patch does no functional changes besides reordering the calls.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
> ---
>  mm/page_alloc.c | 18 +++++-------------
>  1 file changed, 5 insertions(+), 13 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 3f3ea41f8c64..0673db27dd12 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1289,6 +1289,7 @@ static __always_inline bool free_pages_prepare(struct page *page,
>  {
>  	int bad = 0;
>  	bool skip_kasan_poison = should_skip_kasan_poison(page, fpi_flags);

skip_kasan_poison is only used once now, so you could remove the
variable -- unless later code will use it in more than once place again.

> +	bool init = want_init_on_free();
>  
>  	VM_BUG_ON_PAGE(PageTail(page), page);
>  
> @@ -1359,19 +1360,10 @@ static __always_inline bool free_pages_prepare(struct page *page,
>  	 * With hardware tag-based KASAN, memory tags must be set before the
>  	 * page becomes unavailable via debug_pagealloc or arch_free_page.
>  	 */
> -	if (kasan_has_integrated_init()) {
> -		bool init = want_init_on_free();
> -
> -		if (!skip_kasan_poison)
> -			kasan_poison_pages(page, order, init);
> -	} else {
> -		bool init = want_init_on_free();
> -
> -		if (init)
> -			kernel_init_free_pages(page, 1 << order);
> -		if (!skip_kasan_poison)
> -			kasan_poison_pages(page, order, init);
> -	}
> +	if (!skip_kasan_poison)
> +		kasan_poison_pages(page, order, init);
> +	if (init && !kasan_has_integrated_init())
> +		kernel_init_free_pages(page, 1 << order);
>  
>  	/*
>  	 * arch_free_page() can make the page's contents inaccessible.  s390
> -- 
> 2.25.1