Re: [PATCH] mtd: spi-nor: fix DMA unsafe buffer issue in spi_nor_read_sfdp()

[Boris Brezillon <boris.brezillon@free-electrons.com>]

On Thu, 7 Sep 2017 00:50:12 +0200
Cyrille Pitchen <cyrille.pitchen@wedev4u.fr> wrote:

> Le 06/09/2017 à 23:45, Cyrille Pitchen a écrit :
> > spi_nor_read_sfdp() calls nor->read() to read the SFDP data.
> > When the m25p80 driver is used (pretty common case), nor->read() is then
> > implemented by the m25p80_read() function, which is likely to initialize a
> > 'struct spi_transfer' from its buf argument before appending this
> > structure inside the 'struct spi_message' argument of spi_sync().
> > 
> > Besides the SPI sub-system states that both .tx_buf and .rx_buf members of
> > 'struct spi_transfer' must point into dma-safe memory. However, two of the
> > three calls of spi_nor_read_sfdp() were given pointers to stack allocated
> > memory as buf argument, hence not in a dma-safe area.
> > Hopefully, the third and last call of spi_nor_read_sfdp() was already
> > given a kmalloc'ed buffer argument, hence dma-safe.
> > 
> > So this patch fixes this issue by introducing a
> > spi_nor_read_sfdp_dma_unsafe() function which simply wraps the existing
> > spi_nor_read_sfdp() function and uses some kmalloc'ed memory as a bounce
> > buffer.
> > 
> > Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
> > Signed-off-by: Cyrille Pitchen <cyrille.pitchen@wedev4u.fr>
> > ---
> > 
> > Compiled but not tested yet!  
> 
> tested on a sama5d2 xplained board with:
> - an Adesto at25df321a on spi0 (using the m25p80.c driver)
> - a Macronix mx25l25673g on qspi0 (using the atmel-quadspi.c driver)

Cool, that was fast.

> 
> applied on the spi-nor/next branch of l2-mtd

Maybe a bit too fast. You should leave at least one day to
reviewers/testers before applying the patch.

BTW, I was planning on taking the patch directly.

> 
> should be quickly sent as a fix to the MTD pull-request for 4.14
> 
> Sorry for that!
> 
> > 
> >  drivers/mtd/spi-nor/spi-nor.c | 36 +++++++++++++++++++++++++++++++++---
> >  1 file changed, 33 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
> > index cf1d4a15e10a..05254dd6a4a0 100644
> > --- a/drivers/mtd/spi-nor/spi-nor.c
> > +++ b/drivers/mtd/spi-nor/spi-nor.c
> > @@ -1784,7 +1784,7 @@ spi_nor_set_pp_settings(struct spi_nor_pp_command *pp,
> >   * @nor:	pointer to a 'struct spi_nor'
> >   * @addr:	offset in the SFDP area to start reading data from
> >   * @len:	number of bytes to read
> > - * @buf:	buffer where the SFDP data are copied into
> > + * @buf:	buffer where the SFDP data are copied into (dma-safe memory)
> >   *
> >   * Whatever the actual numbers of bytes for address and dummy cycles are
> >   * for (Fast) Read commands, the Read SFDP (5Ah) instruction is always
> > @@ -1829,6 +1829,36 @@ static int spi_nor_read_sfdp(struct spi_nor *nor, u32 addr,
> >  	return ret;
> >  }
> >  
> > +/**
> > + * spi_nor_read_sfdp_dma_unsafe() - read Serial Flash Discoverable Parameters.
> > + * @nor:	pointer to a 'struct spi_nor'
> > + * @addr:	offset in the SFDP area to start reading data from
> > + * @len:	number of bytes to read
> > + * @buf:	buffer where the SFDP data are copied into
> > + *
> > + * Wrap spi_nor_read_sfdp() using a kmalloc'ed bounce buffer as @buf is now not
> > + * guaranteed to be dma-safe.
> > + *
> > + * Return: -ENOMEM if kmalloc() fails, the return code of spi_nor_read_sfdp()
> > + *          otherwise.
> > + */
> > +static int spi_nor_read_sfdp_dma_unsafe(struct spi_nor *nor, u32 addr,
> > +					size_t len, void *buf)
> > +{
> > +	void *dma_safe_buf;
> > +	int ret;
> > +
> > +	dma_safe_buf = kmalloc(len, GFP_KERNEL);
> > +	if (!dma_safe_buf)
> > +		return -ENOMEM;
> > +
> > +	ret = spi_nor_read_sfdp(nor, addr, len, dma_safe_buf);
> > +	memcpy(buf, dma_safe_buf, len);
> > +	kfree(dma_safe_buf);
> > +
> > +	return ret;
> > +}
> > +
> >  struct sfdp_parameter_header {
> >  	u8		id_lsb;
> >  	u8		minor;
> > @@ -2101,7 +2131,7 @@ static int spi_nor_parse_bfpt(struct spi_nor *nor,
> >  		    bfpt_header->length * sizeof(u32));
> >  	addr = SFDP_PARAM_HEADER_PTP(bfpt_header);
> >  	memset(&bfpt, 0, sizeof(bfpt));
> > -	err = spi_nor_read_sfdp(nor,  addr, len, &bfpt);
> > +	err = spi_nor_read_sfdp_dma_unsafe(nor,  addr, len, &bfpt);
> >  	if (err < 0)
> >  		return err;
> >  
> > @@ -2243,7 +2273,7 @@ static int spi_nor_parse_sfdp(struct spi_nor *nor,
> >  	int i, err;
> >  
> >  	/* Get the SFDP header. */
> > -	err = spi_nor_read_sfdp(nor, 0, sizeof(header), &header);
> > +	err = spi_nor_read_sfdp_dma_unsafe(nor, 0, sizeof(header), &header);
> >  	if (err < 0)
> >  		return err;
> >  
> >   
>