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

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Date:   Wed, 10 May 2017 09:42:43 +0100
From:   Phil Elwell <phil@...pberrypi.org>
To:     Stefan Wahren <stefan.wahren@...e.com>,
        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

On 04/05/2017 18:51, Stefan Wahren wrote:
> 
>> 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

Thanks, Stefan.

Is there no feedback other on this patch? It's been in the rpi-4.11.y downstream
branch for a week now with favourable results - see issue
https://github.com/raspberrypi/linux/issues/1977 and pr
https://github.com/raspberrypi/linux/pull/1987.

Phil