Re: [PATCH] mtd: spi-nor: Fix Cadence QSPI page fault kernel panic

[Thor Thayer]

Hi Vignesh,

On 11/14/18 6:00 AM, Vignesh R wrote:
> Hi,
>
> On 13/11/18 11:02 PM, thor.thayer@xxxxxxxxxxxxxxx wrote:
> > From: Thor Thayer <thor.thayer@xxxxxxxxxxxxxxx>
> >
> > The current Cadence QSPI driver caused a kernel panic sporadically
> > when writing to QSPI. The problem was caused by writing more bytes
> > than needed because the QSPI operated on 4 bytes at a time.
> > <snip>
> > [   11.202044] Unable to handle kernel paging request at virtual address bffd3000
> > [   11.209254] pgd = e463054d
> > [   11.211948] [bffd3000] *pgd=2fffb811, *pte=00000000, *ppte=00000000
> > [   11.218202] Internal error: Oops: 7 [#1] SMP ARM
> > [   11.222797] Modules linked in:
> > [   11.225844] CPU: 1 PID: 1317 Comm: systemd-hwdb Not tainted 4.17.7-d0c45cd44a8f
> > [   11.235796] Hardware name: Altera SOCFPGA Arria10
> > [   11.240487] PC is at __raw_writesl+0x70/0xd4
> > [   11.244741] LR is at cqspi_write+0x1a0/0x2cc
> > </snip>
> > On a page boundary limit the number of bytes copied from the tx buffer
> > to remain within the page.
> >
> > This patch uses a temporary buffer to hold the 4 bytes to write and then
> > copies only the bytes required from the tx buffer. A min() function is
> > used to limit the length to prevent buffer indexing overflows.
> >
> > Reported-by: Adrian Amborzewicz <adrian.ambrozewicz@xxxxxxxxx>
> > Signed-off-by: Thor Thayer <thor.thayer@xxxxxxxxxxxxxxx>
> > ---
> >   drivers/mtd/spi-nor/cadence-quadspi.c | 19 ++++++++++++++++---
> >   1 file changed, 16 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/mtd/spi-nor/cadence-quadspi.c b/drivers/mtd/spi-nor/cadence-quadspi.c
> > index d846428ef038..3659d94b4d2f 100644
> > --- a/drivers/mtd/spi-nor/cadence-quadspi.c
> > +++ b/drivers/mtd/spi-nor/cadence-quadspi.c
> > @@ -644,9 +644,23 @@ static int cqspi_indirect_write_execute(struct spi_nor *nor, loff_t to_addr,
> >   		ndelay(cqspi->wr_delay);
> >   
> >   	while (remaining > 0) {
> > +		size_t write_words, mod_bytes;
> > +
> >   		write_bytes = remaining > page_size ? page_size : remaining;
> > -		iowrite32_rep(cqspi->ahb_base, txbuf,
> > -			      DIV_ROUND_UP(write_bytes, 4));
> > +		write_words = write_bytes / 4;
> > +		mod_bytes = write_bytes % 4;
> > +		/* Write 4 bytes at a time then single bytes. */
> > +		if (write_words) {
> > +			iowrite32_rep(cqspi->ahb_base, txbuf, write_words);
> > +			txbuf += (write_words * 4);
> > +		}
> > +		if (mod_bytes) {
> > +			unsigned int temp = 0xFFFFFFFF;
> > +
> > +			memcpy(&temp, txbuf, min(sizeof(temp), mod_bytes));
>
> Sorry, I dont understand why min() is required here since:
> 	mod_bytes = write_bytes % 4;
> Doesn't that ensure mod_bytes < sizeof(temp)?

Yes, good point. I was being overly cautious with the memcpy buffers. I 
will re-spin and re-submit. Thanks!

> > +			iowrite32(temp, cqspi->ahb_base);
> > +			txbuf += mod_bytes;
> > +		}
> >   
> >   		if (!wait_for_completion_timeout(&cqspi->transfer_complete,
> >   					msecs_to_jiffies(CQSPI_TIMEOUT_MS))) {
> > @@ -655,7 +669,6 @@ static int cqspi_indirect_write_execute(struct spi_nor *nor, loff_t to_addr,
> >   			goto failwr;
> >   		}
> >   
> > -		txbuf += write_bytes;
> >   		remaining -= write_bytes;
> >   
> >   		if (remaining > 0)