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SubjectRe: [PATCH] mtd: spi-nor: Fix Cadence QSPI page fault kernel panic
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Hi Vignesh,

On 11/14/18 6:00 AM, Vignesh R wrote:
> Hi,
>
> On 13/11/18 11:02 PM, thor.thayer@linux.intel.com wrote:
>> From: Thor Thayer <thor.thayer@linux.intel.com>
>>
>> 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@intel.com>
>> Signed-off-by: Thor Thayer <thor.thayer@linux.intel.com>
>> ---
>> 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)
>>
>

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