Re: [PATCH] mtk-sd: Fix a pagefault in dma_unmap_sg() for not prepared data
From: Ulf Hansson <hidden>
Date: 2025-06-09 14:26:02
Also in:
linux-mediatek, linux-mmc, lkml
On Thu, 5 Jun 2025 at 03:07, Masami Hiramatsu (Google) [off-list ref] wrote:
From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
mtk-msdc driver causes a kernel crash after swiotlb buffer is full.
---
mtk-msdc 11240000.mmc: swiotlb buffer is full (sz: 16384 bytes), total 32768 (slots), used 32732 (slots)
mtk-msdc 11240000.mmc: msdc_track_cmd_data: cmd=18 arg=0397A6F8; host->error=0x00000004
Unable to handle kernel paging request at virtual address ffffffffc0001fc0
---
When swiotlb buffer is full, the dma_map_sg() returns 0 to
msdc_prepare_data(), but it does not check it and sets the
MSDC_PREPARE_FLAG.
swiotlb_tbl_map_single() /* prints "swiotlb buffer is full" */
<-swiotlb_map()
<-dma_direct_map_page()
<-dma_direct_map_sg()
<-__dma_map_sg_attrs()
<-dma_map_sg_attrs()
<-dma_map_sg() /* returns 0 (pages mapped) */
<-msdc_prepare_data()
Then, the msdc_unprepare_data() checks MSDC_PREPARE_FLAG and calls
dma_unmap_sg() with unmapped pages. It causes a page fault.
To fix this problem, Do not set MSDC_PREPARE_FLAG if dma_map_sg()
fails because this is not prepared.
Fixes: 208489032bdd ("mmc: mediatek: Add Mediatek MMC driver")
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>Applied for fixes and by adding a stable-tag, thanks! Note that it looked like the patch was not entirely correctly formatted, but I fixed it up when applying. Please have a look at the fixes branch to make sure things look okay to you. Kind regards Uffe
quoted hunk ↗ jump to hunk
--- drivers/mmc/host/mtk-sd.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)diff --git a/drivers/mmc/host/mtk-sd.c b/drivers/mmc/host/mtk-sd.c index 345ea91629e0..3594010bc229 100644 --- a/drivers/mmc/host/mtk-sd.c +++ b/drivers/mmc/host/mtk-sd.c@@ -827,9 +827,10 @@ static inline void msdc_dma_setup(struct msdc_host *host, struct msdc_dma *dma, static void msdc_prepare_data(struct msdc_host *host, struct mmc_data *data) { if (!(data->host_cookie & MSDC_PREPARE_FLAG)) { - data->host_cookie |= MSDC_PREPARE_FLAG; data->sg_count = dma_map_sg(host->dev, data->sg, data->sg_len, mmc_get_dma_dir(data)); + if (data->sg_count) + data->host_cookie |= MSDC_PREPARE_FLAG; } }