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Date:   Tue, 5 Jul 2022 19:58:34 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     LABBE Corentin <clabbe@baylibre.com>
Cc:     Christoph Hellwig <hch@lst.de>,
        Ben Dooks <ben.dooks@codethink.co.uk>,
        herbert@gondor.apana.org.au, heiko@sntech.de,
        linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-riscv@lists.infradead.org, linux-sunxi@lists.linux.dev
Subject: Re: [RFC PATCH] crypto: flush poison data
Message-ID: <20220705175834.GA15815@lst.de>
References: <20220701132735.1594822-1-clabbe@baylibre.com> <4570f6d8-251f-2cdb-1ea6-c3a8d6bb9fcf@codethink.co.uk> <YsP0eekTthD4jWGV@Red> <20220705164213.GA14484@lst.de> <YsR7O4q4IRI14Wkc@Red>
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On Tue, Jul 05, 2022 at 07:56:11PM +0200, LABBE Corentin wrote:
> My problem is that a dma_sync on the data buffer corrupt the poison buffer as collateral dommage.
> Probably because the sync operate on a larger region than the requested dma_sync length.
> So I try to flush poison data in the cryptoAPI.

Data structures that are DMAed to must be aligned to
the value returned by dma_get_cache_alignment(), as non-coherent DMA
by definition can disturb the data inside that boundary.  That is not
a bug but fundamentally part of how DMA works when the device attachment
is not cache coherent.