linux-kernel - Re: [PATCH v3 15/24] media: exynos4-is: Remove call to memset after dma_alloc

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Message-ID: <CABXRUiQ_N=N=weMnRea4d6PXjfghta=U1xhdv-tZpSvaGBnXGg@mail.gmail.com>
Date:   Mon, 15 Jul 2019 17:43:45 +0800
From:   Fuqian Huang <huangfq.daxian@...il.com>
To:     Sylwester Nawrocki <s.nawrocki@...sung.com>
Cc:     Kyungmin Park <kyungmin.park@...sung.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Kukjin Kim <kgene@...nel.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        linux-media@...r.kernel.org,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        linux-samsung-soc@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 15/24] media: exynos4-is: Remove call to memset after dma_alloc_coherent

Sylwester Nawrocki <s.nawrocki@...sung.com> 於 2019年7月15日週一 下午5:00寫道：
>
> On 7/15/19 05:18, Fuqian Huang wrote:
> > In commit 518a2f1925c3
> > ("dma-mapping: zero memory returned from dma_alloc_*"),
> > dma_alloc_coherent has already zeroed the memory.
> > So memset is not needed
>
> I can't see any changes in the above mentioned commit that would
> make dma_alloc_coherent() (arm_coherent_dma_alloc()) zeroing its
> returned memory. Maybe you need to add a reference to some other
> instead?
>
In the last version patch set, I referenced the commit af7ddd8a627c
("Merge tag 'dma-mapping-4.21' of
git://git.infradead.org/users/hch/dma-mapping")
in the commit log.
The merged commit mentions that
"ensure dma_alloc_coherent returns zeroed memory to
avoid kernel data leaks through userspace.
We already did this for most common architectures,
but this ensures we do it everywhere."
dma_alloc_coherent has already zeroed the memory during allocation
and the commit also deprecates dma_zalloc_coherent.
Greg and other maintainer told me to use the actual commit
rather than the merged commit.
So I reference the commit that ensures the dma_alloc_coherent to
returns zeroed memory every where.
Maybe this belongs to the `most common achitectures` and is not impacted
by the mentioned change.
Should I rewrite the commit log? Just mention that dma_alloc_coherent
has already zeroed the memory and not to reference the commit?