From: Paul Burton Date: Fri, 11 Nov 2016 14:22:36 +0000 (+0000) Subject: mmc: sd: Meet alignment requirements for raw_ssr DMA X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=e85baa8868b016513c0f5738362402495b1a66a5;p=linux-beck.git mmc: sd: Meet alignment requirements for raw_ssr DMA The mmc_read_ssr() function results in DMA to the raw_ssr member of struct mmc_card, which is not guaranteed to be cache line aligned & thus might not meet the requirements set out in Documentation/DMA-API.txt: Warnings: Memory coherency operates at a granularity called the cache line width. In order for memory mapped by this API to operate correctly, the mapped region must begin exactly on a cache line boundary and end exactly on one (to prevent two separately mapped regions from sharing a single cache line). Since the cache line size may not be known at compile time, the API will not enforce this requirement. Therefore, it is recommended that driver writers who don't take special care to determine the cache line size at run time only map virtual regions that begin and end on page boundaries (which are guaranteed also to be cache line boundaries). On some systems where DMA is non-coherent this can lead to us losing data that shares cache lines with the raw_ssr array. Fix this by kmalloc'ing a temporary buffer to perform DMA into. kmalloc will ensure the buffer is suitably aligned, allowing the DMA to be performed without any loss of data. Signed-off-by: Paul Burton Fixes: 5275a652d296 ("mmc: sd: Export SD Status via “ssr” device attribute") Cc: Signed-off-by: Ulf Hansson --- diff --git a/drivers/mmc/core/sd.c b/drivers/mmc/core/sd.c index deb90c2ff6b4..a614f37faf27 100644 --- a/drivers/mmc/core/sd.c +++ b/drivers/mmc/core/sd.c @@ -223,6 +223,7 @@ static int mmc_decode_scr(struct mmc_card *card) static int mmc_read_ssr(struct mmc_card *card) { unsigned int au, es, et, eo; + u32 *raw_ssr; int i; if (!(card->csd.cmdclass & CCC_APP_SPEC)) { @@ -231,14 +232,21 @@ static int mmc_read_ssr(struct mmc_card *card) return 0; } - if (mmc_app_sd_status(card, card->raw_ssr)) { + raw_ssr = kmalloc(sizeof(card->raw_ssr), GFP_KERNEL); + if (!raw_ssr) + return -ENOMEM; + + if (mmc_app_sd_status(card, raw_ssr)) { pr_warn("%s: problem reading SD Status register\n", mmc_hostname(card->host)); + kfree(raw_ssr); return 0; } for (i = 0; i < 16; i++) - card->raw_ssr[i] = be32_to_cpu(card->raw_ssr[i]); + card->raw_ssr[i] = be32_to_cpu(raw_ssr[i]); + + kfree(raw_ssr); /* * UNSTUFF_BITS only works with four u32s so we have to offset the