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

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Date:   Wed, 10 May 2017 11:06:26 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Phil Elwell <phil@...pberrypi.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 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...

thanks,

greg k-h