linux-kernel - Re: [PATCH v5 2/9] scatterlist: Add a flag for the restricted memory

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Message-ID: <779ce30a657754ff945ebd32b66e1c644635e84d.camel@mediatek.com>
Date: Mon, 20 May 2024 07:58:15 +0000
From: Yong Wu (吴勇) <Yong.Wu@...iatek.com>
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	Youlin Pei (裴友林) <youlin.pei@...iatek.com>
Subject: Re: [PATCH v5 2/9] scatterlist: Add a flag for the restricted memory

On Thu, 2024-05-16 at 10:17 +0200, Christian König wrote:
>  	 
> External email : Please do not click links or open attachments until
> you have verified the sender or the content.
>  Am 15.05.24 um 13:23 schrieb Yong Wu:
> > Introduce a FLAG for the restricted memory which means the memory
> is
> > protected by TEE or hypervisor, then it's inaccessiable for kernel.
> >
> > Currently we don't use sg_dma_unmark_restricted, thus this
> interface
> > has not been added.
> 
> Why should that be part of the scatterlist? It doesn't seem to
> affect 
> any of it's functionality.
> 
> As far as I can see the scatterlist shouldn't be the transport of
> this 
> kind of information.

Thanks for the review. I will remove this.

In our user scenario, DRM will import these buffers and check if this
is a restricted buffer. If yes, it will use secure GCE takes over.

If this judgment is not suitable to be placed in scatterlist. I don't
know if it is ok to limit this inside dma-buf. Adding such an
interface:

static bool dma_buf_is_restricted(struct dma_buf *dmabuf)
{
	return !strncmp(dmabuf->exp_name, "restricted", 10);
}

Thanks.

> 
> Regards,
> Christian.
> 
> >
> > Signed-off-by: Yong Wu <yong.wu@...iatek.com>
> > ---
> >   include/linux/scatterlist.h | 34
> ++++++++++++++++++++++++++++++++++
> >   1 file changed, 34 insertions(+)
> >
> > diff --git a/include/linux/scatterlist.h
> b/include/linux/scatterlist.h
> > index 77df3d7b18a6..a6ad9018eca0 100644
> > --- a/include/linux/scatterlist.h
> > +++ b/include/linux/scatterlist.h
> > @@ -282,6 +282,7 @@ static inline void sg_unmark_end(struct
> scatterlist *sg)
> >   
> >   #define SG_DMA_BUS_ADDRESS(1 << 0)
> >   #define SG_DMA_SWIOTLB(1 << 1)
> > +#define SG_DMA_RESTRICTED(2 << 1)
> >   
> >   /**
> >    * sg_dma_is_bus_address - Return whether a given segment was
> marked
> > @@ -352,6 +353,31 @@ static inline void sg_dma_mark_swiotlb(struct
> scatterlist *sg)
> >   sg->dma_flags |= SG_DMA_SWIOTLB;
> >   }
> >   
> > +/**
> > + * sg_dma_mark_restricted - Mark the scatterlist for restricted
> buffer.
> > + * @sg:SG entry
> > + *
> > + * Description:
> > + *   Marks a a scatterlist for the restricted buffer that may be
> inaccessiable
> > + *   in kernel if it is protected.
> > + */
> > +static inline void sg_dma_mark_restricted(struct scatterlist *sg)
> > +{
> > +sg->dma_flags |= SG_DMA_RESTRICTED;
> > +}
> > +
> > +/**
> > + * sg_dma_is_restricted - Return whether the scatterlist was
> marked as restricted
> > + *                        buffer.
> > + * @sg:SG entry
> > + *
> > + * Description:
> > + *   Returns true if the scatterlist was marked as restricted
> buffer.
> > + */
> > +static inline bool sg_dma_is_restricted(struct scatterlist *sg)
> > +{
> > +return sg->dma_flags & SG_DMA_RESTRICTED;
> > +}
> >   #else
> >   
> >   static inline bool sg_dma_is_bus_address(struct scatterlist *sg)
> > @@ -372,6 +398,14 @@ static inline void sg_dma_mark_swiotlb(struct
> scatterlist *sg)
> >   {
> >   }
> >   
> > +static inline bool sg_dma_is_restricted(struct scatterlist *sg)
> > +{
> > +return false;
> > +}
> > +
> > +static inline void sg_dma_mark_restrited(struct scatterlist *sg)
> > +{
> > +}
> >   #endif/* CONFIG_NEED_SG_DMA_FLAGS */
> >   
> >   /**
> 
>