linux-kernel - Re: [PATCH] mm: add ___GFP_NOINIT flag which disables zeroing on alloc

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Message-ID: <YGF09yYtxeNj4Bcc@unreal>
Date:   Mon, 29 Mar 2021 09:34:31 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Hyunsoon Kim <h10.kim@...sung.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, dseok.yi@...sung.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: add ___GFP_NOINIT flag which disables zeroing on
 alloc

On Mon, Mar 29, 2021 at 02:29:10PM +0900, Hyunsoon Kim wrote:
> This patch allows programmer to avoid zero initialization on page
> allocation even when the kernel config "CONFIG_INIT_ON_ALLOC_DEFAULT"
> is enabled. The configuration is made to prevent uninitialized
> heap memory flaws, and Android has applied this for security and
> deterministic execution times. Please refer to below.
> 
> https://android-review.googlesource.com/c/kernel/common/+/1235132
> 
> However, there is a case that the zeroing page memory is unnecessary
> when the page is used on specific purpose and will be zeroed
> automatically by hardware that accesses the memory through DMA.
> For instance, page allocation used for IP packet reception from Exynos
> modem is solely used for packet reception. Although the page will be
> freed eventually and reused for some other purpose, initialization at
> that moment of reuse will be sufficient to avoid uninitialized heap
> memory flaws. To support this kind of control, this patch creates new
> gfp type called ___GFP_NOINIT, that allows no zeroing at the moment
> of page allocation, called by many related APIs such as page_frag_alloc,
> alloc_pages, etc.
> 
> Signed-off-by: Hyunsoon Kim <h10.kim@...sung.com>
> ---
>  include/linux/gfp.h | 2 ++
>  include/linux/mm.h  | 4 +++-
>  2 files changed, 5 insertions(+), 1 deletion(-)

Let's assume that we will use this new flag, and users are smart enough
to figure when it needs to be used, what will be the performance gain?

Thanks