Il 05/06/25 03:07, Masami Hiramatsu (Google) ha scritto:

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>

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>