linux-kernel - Re: [PATCHv2] mtd: spi-nor: Fix Cadence QSPI page fault kernel panic

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Date:   Fri, 20 Apr 2018 22:48:53 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     thor.thayer@...ux.intel.com
Cc:     cyrille.pitchen@...ev4u.fr, marek.vasut@...il.com,
        dwmw2@...radead.org, computersforpeace@...il.com, richard@....at,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2] mtd: spi-nor: Fix Cadence QSPI page fault kernel
 panic

On Mon, 26 Mar 2018 09:12:17 -0500
thor.thayer@...ux.intel.com wrote:

> From: Thor Thayer <thor.thayer@...ux.intel.com>
> 
> The current Cadence QSPI driver caused a kernel panic when loading
> a Root Filesystem from QSPI. The problem was caused by reading more
> bytes than needed because the QSPI operated on 4 bytes at a time.
> <snip>
> [    7.947754] spi_nor_read[1048]:from 0x037cad74, len 1 [bfe07fff]
> [    7.956247] cqspi_read[910]:offset 0x58502516, buffer=bfe07fff
> [    7.956247]
> [    7.966046] Unable to handle kernel paging request at virtual
> address bfe08002
> [    7.973239] pgd = eebfc000
> [    7.975931] [bfe08002] *pgd=2fffb811, *pte=00000000, *ppte=00000000
> </snip>
> Notice above how only 1 byte needed to be read but by reading 4 bytes
> into the end of a mapped page, an unrecoverable page fault occurred.
> 
> This patch uses a temporary buffer to hold the 4 bytes read and then
> copies only the bytes required into the buffer. A min() function is
> used to limit the length to prevent buffer overflows.
> 
> Request testing of this patch on other platforms. This was tested
> on the Intel Arria10 SoCFPGA DevKit.
> 
> Signed-off-by: Thor Thayer <thor.thayer@...ux.intel.com>

Can you add a Fixes and Cc-stable tag?

> ---
> v2  Changes to only write dangling bytes at end of transfer since
>       previous patch may have multiple dangling byte transfers.
>     Remove write patch since no errors reported and write timeout
>       needs more investigation.
> ---
>  drivers/mtd/spi-nor/cadence-quadspi.c | 19 +++++++++++++++++--
>  1 file changed, 17 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mtd/spi-nor/cadence-quadspi.c b/drivers/mtd/spi-nor/cadence-quadspi.c
> index 4b8e9183489a..5872f31eaa60 100644
> --- a/drivers/mtd/spi-nor/cadence-quadspi.c
> +++ b/drivers/mtd/spi-nor/cadence-quadspi.c
> @@ -501,7 +501,9 @@ static int cqspi_indirect_read_execute(struct spi_nor *nor, u8 *rxbuf,
>  	void __iomem *reg_base = cqspi->iobase;
>  	void __iomem *ahb_base = cqspi->ahb_base;
>  	unsigned int remaining = n_rx;
> +	unsigned int mod_bytes = n_rx % 4;
>  	unsigned int bytes_to_read = 0;
> +	u8 *rxbuf_end = rxbuf + n_rx;
>  	int ret = 0;
>  
>  	writel(from_addr, reg_base + CQSPI_REG_INDIRECTRDSTARTADDR);
> @@ -530,11 +532,24 @@ static int cqspi_indirect_read_execute(struct spi_nor *nor, u8 *rxbuf,
>  		}
>  
>  		while (bytes_to_read != 0) {
> +			unsigned int word_remain = round_down(remaining, 4);
> +
>  			bytes_to_read *= cqspi->fifo_width;
>  			bytes_to_read = bytes_to_read > remaining ?
>  					remaining : bytes_to_read;
> -			ioread32_rep(ahb_base, rxbuf,
> -				     DIV_ROUND_UP(bytes_to_read, 4));
> +			bytes_to_read = round_down(bytes_to_read, 4);
> +			/* Read 4 byte word chunks then single bytes */
> +			if (bytes_to_read) {
> +				ioread32_rep(ahb_base, rxbuf,
> +					     (bytes_to_read / 4));
> +			} else if (!word_remain && mod_bytes) {
> +				unsigned int temp = ioread32(ahb_base);
> +
> +				bytes_to_read = mod_bytes;
> +				memcpy(rxbuf, &temp, min((unsigned int)
> +							 (rxbuf_end - rxbuf),
> +							 bytes_to_read));
> +			}
>  			rxbuf += bytes_to_read;
>  			remaining -= bytes_to_read;
>  			bytes_to_read = cqspi_get_rd_sram_level(cqspi);