linux-kernel - Re: [RFC PATCH] crypto: flush poison data

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Date:   Tue, 5 Jul 2022 19:58:34 +0200
From:   Christoph Hellwig <hch@....de>
To:     LABBE Corentin <clabbe@...libre.com>
Cc:     Christoph Hellwig <hch@....de>,
        Ben Dooks <ben.dooks@...ethink.co.uk>,
        herbert@...dor.apana.org.au, heiko@...ech.de,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-sunxi@...ts.linux.dev
Subject: Re: [RFC PATCH] crypto: flush poison data

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.