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Date:   Thu, 26 Jul 2018 17:09:40 +0200
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Ben Hutchings <ben.hutchings@codethink.co.uk>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Maxime Chevallier <maxime.chevallier@bootlin.com>,
        Mark Brown <broonie@kernel.org>,
        Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Subject: Re: [PATCH 4.4 101/105] spi: Fix scatterlist elements size in
 spi_map_buf
Message-ID: <20180726150940.GD27305@kroah.com>
References: <20180701153149.382300170@linuxfoundation.org>
 <20180701153156.693937436@linuxfoundation.org>
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On Fri, Jul 20, 2018 at 08:23:44PM +0100, Ben Hutchings wrote:
> On Sun, 2018-07-01 at 18:02 +0200, Greg Kroah-Hartman wrote:
> > 4.4-stable review patch.??If anyone has any objections, please let me know.
> > 
> > ------------------
> > 
> > From: Maxime Chevallier <maxime.chevallier@bootlin.com>
> > 
> > commit ce99319a182fe766be67f96338386f3ec73e321c upstream.
> > 
> > When SPI transfers can be offloaded using DMA, the SPI core need to
> > build a scatterlist to make sure that the buffer to be transferred is
> > dma-able.
> > 
> > This patch fixes the scatterlist entry size computation in the case
> > where the maximum acceptable scatterlist entry supported by the DMA
> > controller is less than PAGE_SIZE, when the buffer is vmalloced.
> > 
> > For each entry, the actual size is given by the minimum between the
> > desc_len (which is the max buffer size supported by the DMA controller)
> > and the remaining buffer length until we cross a page boundary.
> > 
> > Fixes: 65598c13fd66 ("spi: Fix per-page mapping of unaligned vmalloc-ed buffer")
> > Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
> > Signed-off-by: Mark Brown <broonie@kernel.org>
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > ---
> > ?drivers/spi/spi.c |???10 ++++++++--
> > ?1 file changed, 8 insertions(+), 2 deletions(-)
> > 
> > --- a/drivers/spi/spi.c
> > +++ b/drivers/spi/spi.c
> > @@ -707,8 +707,14 @@ static int spi_map_buf(struct spi_master
> > ?	for (i = 0; i < sgs; i++) {
> > ?
> > ?		if (vmalloced_buf) { 
> > -			min = min_t(size_t,
> > -				????len, desc_len - offset_in_page(buf));
> > +			/*
> > +			?* Next scatterlist entry size is the minimum between
> > +			?* the desc_len and the remaining buffer length that
> > +			?* fits in a page.
> > +			?*/
> > +			min = min_t(size_t, desc_len,
> > +				????min_t(size_t, len,
> > +					??PAGE_SIZE - offset_in_page(buf)));
> > ?			vm_page = vmalloc_to_page(buf);
> > ?			if (!vm_page) {
> > ?				sg_free_table(sgt);
> 
> I think this makes sense upstream, but in 4.4 it seems to be a no-op
> since desc_len is always set to PAGE_SIZE when vmalloced_buf is true.
> This fix depends on (at least) commit df88e91bbfd1 "spi: respect the
> maximum segment size of DMA device" which went into 4.6.

Good catch.  I'll leave it as-is for now though.

thanks,

greg k-h