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Date:   Tue, 2 Nov 2021 07:43:56 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Walter Wu <walter-zh.wu@mediatek.com>
Cc:     Ard Biesheuvel <ardb@kernel.org>, Christoph Hellwig <hch@lst.de>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Linux IOMMU <iommu@lists.linux-foundation.org>,
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        wsd_upstream <wsd_upstream@mediatek.com>,
        linux-mediatek@lists.infradead.org,
        Andrew Morton <akpm@linux-foundation.org>,
        Will Deacon <will@kernel.org>
Subject: Re: [PATCH] dma-direct: fix DMA_ATTR_NO_KERNEL_MAPPING
Message-ID: <20211102064356.GB27749@lst.de>
References: <20211101031558.7184-1-walter-zh.wu@mediatek.com> <CAMj1kXGqOzHM+J30TXR3-uZPkjHBCXB4CMkzZjHbbmptyU5W9w@mail.gmail.com> <76840b40fcf26a65467931a73f236982ad39989c.camel@mediatek.com> <CAMj1kXFrUrThJFDJ0Q9qjDemcEovQVMtO20KbdnLccp7VfyVwA@mail.gmail.com> <c9f74d817aa1ae1cceaee9ec226d39bbdf2c5c48.camel@mediatek.com>
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On Tue, Nov 02, 2021 at 11:21:16AM +0800, Walter Wu wrote:
> Our platform is arch64. We need a dynamic allocated buffer from CMA is
> not to read by CPU peculative execution, so we need to remove its
> kernel mapping.

If your CPU speculates into unused kernel direct mappings your have
a worse problem than this, because all the dma coherent allocations for
non-coherent devices still have a cachable direct mapping.  Will
mentioned he wanted to look into getting rid of that mapping now that
the core dma code has the infrastucture for that, so adding him here.