linux-kernel - Re: [PATCH v3 04/24] dmaengine: qcom_hidma: Remove call to memset after dmam_alloc

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Message-ID: <CABXRUiQXweOLRTpdyhx9xT_B1VBmoSoNm=_+Qr4prmz7u1QRFA@mail.gmail.com>
Date:   Mon, 15 Jul 2019 13:43:23 +0800
From:   Fuqian Huang <huangfq.daxian@...il.com>
To:     Sinan Kaya <Okaya@...nel.org>
Cc:     Andy Gross <agross@...nel.org>,
        David Brown <david.brown@...aro.org>,
        Vinod Koul <vkoul@...nel.org>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        linux-arm-msm@...r.kernel.org, dmaengine@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Robin Murphy <robin.murphy@....com>,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH v3 04/24] dmaengine: qcom_hidma: Remove call to memset
 after dmam_alloc_coherent

Sinan Kaya <Okaya@...nel.org> 於 2019年7月15日週一 下午12:17寫道：
>
> On 7/14/2019 11:17 PM, 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.
> >
> > Signed-off-by: Fuqian Huang <huangfq.daxian@...il.com>
>
> I don't see SWIO or ARM64 IOMMU drivers getting impacted by
> the mentioned change above (518a2f1925c3).
>
> How does this new behavior apply globally?
>
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?