linux-kernel - Re: [PATCH] mtk-sd: Fix a pagefault in dma_unmap

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Message-Id: <20250610134114.5ce2c929b683be6e4f228f2b@kernel.org>
Date: Tue, 10 Jun 2025 13:41:14 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Ulf Hansson <ulf.hansson@...aro.org>
Cc: Chaotian Jing <chaotian.jing@...iatek.com>, Matthias Brugger
 <matthias.bgg@...il.com>, AngeloGioacchino Del Regno
 <angelogioacchino.delregno@...labora.com>, Sergey Senozhatsky
 <senozhatsky@...omium.org>, linux-mmc@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH] mtk-sd: Fix a pagefault in dma_unmap_sg() for not
 prepared data

On Mon, 9 Jun 2025 16:25:24 +0200
Ulf Hansson <ulf.hansson@...aro.org> wrote:

> On Thu, 5 Jun 2025 at 03:07, Masami Hiramatsu (Google)
> <mhiramat@...nel.org> wrote:
> >
> > From: Masami Hiramatsu (Google) <mhiramat@...nel.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@...nel.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.

Thank for applying and fixing!

Thank you,

> 
> Kind regards
> Uffe
> 
> 
> 
> > ---
> >  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;
> >         }
> >  }
> >
> >


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>