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

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Date:   Wed, 10 May 2017 10:11:04 +0100
From:   Phil Elwell <phil@...pberrypi.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Stefan Wahren <stefan.wahren@...e.com>, devel@...verdev.osuosl.org,
        daniels@...labora.com, Lee Jones <lee@...nel.org>,
        linux-kernel@...r.kernel.org,
        Noralf Trønnes <noralf@...nnes.org>,
        linux-rpi-kernel <linux-rpi-kernel@...ts.infradead.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] staging: vc04_services: Fix bulk cache maintenance

On 10/05/2017 10:06, Greg Kroah-Hartman wrote:
> On Wed, May 10, 2017 at 09:42:43AM +0100, Phil Elwell wrote:
>> 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.
> 
> It's the middle of the merge window, I can't do anything with this
> until after 4.12-rc1 comes out.  Please be patient...

Yes, of course - that's the kind of feedback I was looking for.

Thanks,

Phil