linux-kernel - Re: [PATCH] staging: vc04_services: Fix bulk cache maintenance

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Date:   Thu, 4 May 2017 19:51:10 +0200 (CEST)
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     Phil Elwell <phil@...pberrypi.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Lee Jones <lee@...nel.org>, linux-kernel@...r.kernel.org,
        devel@...verdev.osuosl.org, daniels@...labora.com,
        linux-rpi-kernel <linux-rpi-kernel@...ts.infradead.org>,
        linux-arm-kernel@...ts.infradead.org,
        Noralf Trønnes <noralf@...nnes.org>
Subject: Re: [PATCH] staging: vc04_services: Fix bulk cache maintenance


> Phil Elwell <phil@...pberrypi.org> hat am 4. Mai 2017 um 11:58 geschrieben:
> 
> 
> vchiq_arm supports transfers less than one page and at arbitrary
> alignment, using the dma-mapping API to perform its cache maintenance
> (even though the VPU drives the DMA hardware). Read (DMA_FROM_DEVICE)
> operations use cache invalidation for speed, falling back to
> clean+invalidate on partial cache lines, with writes (DMA_TO_DEVICE)
> using flushes.
> 
> If a read transfer has ends which aren't page-aligned, performing cache
> maintenance as if they were whole pages can lead to memory corruption
> since the partial cache lines at the ends (and any cache lines before or
> after the transfer area) will be invalidated. This bug was masked until
> the disabling of the cache flush in flush_dcache_page().
> 
> Honouring the requested transfer start- and end-points prevents the
> corruption.
> 
> Fixes: cf9caf192988 ("staging: vc04_services: Replace dmac_map_area with dmac_map_sg")
> Signed-off-by: Phil Elwell <phil@...pberrypi.org>

Reported-by: Stefan Wahren <stefan.wahren@...e.com>
Tested-by: Stefan Wahren <stefan.wahren@...e.com>

In order to clarify the context of this issue:

http://lists.infradead.org/pipermail/linux-rpi-kernel/2017-April/006149.html