Re: [PATCH v15 10/12] swiotlb: Add restricted DMA pool initialization

[Claire Chang]

On Tue, Aug 24, 2021 at 10:26 PM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
>
> Hi Claire,
>
> On Thu, Jun 24, 2021 at 11:55:24PM +0800, Claire Chang wrote:
> > Add the initialization function to create restricted DMA pools from
> > matching reserved-memory nodes.
> >
> > Regardless of swiotlb setting, the restricted DMA pool is preferred if
> > available.
> >
> > The restricted DMA pools provide a basic level of protection against the
> > DMA overwriting buffer contents at unexpected times. However, to protect
> > against general data leakage and system memory corruption, the system
> > needs to provide a way to lock down the memory access, e.g., MPU.
> >
> > Signed-off-by: Claire Chang <tientzu@xxxxxxxxxxxx>
> > Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> > Tested-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> > Tested-by: Will Deacon <will@xxxxxxxxxx>
> > ---
> >  include/linux/swiotlb.h |  3 +-
> >  kernel/dma/Kconfig      | 14 ++++++++
> >  kernel/dma/swiotlb.c    | 76 +++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 92 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
> > index 3b9454d1e498..39284ff2a6cd 100644
> > --- a/include/linux/swiotlb.h
> > +++ b/include/linux/swiotlb.h
> > @@ -73,7 +73,8 @@ extern enum swiotlb_force swiotlb_force;
> >   *           range check to see if the memory was in fact allocated by this
> >   *           API.
> >   * @nslabs:  The number of IO TLB blocks (in groups of 64) between @start and
> > - *           @end. This is command line adjustable via setup_io_tlb_npages.
> > + *           @end. For default swiotlb, this is command line adjustable via
> > + *           setup_io_tlb_npages.
> >   * @used:    The number of used IO TLB block.
> >   * @list:    The free list describing the number of free entries available
> >   *           from each index.
> > diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
> > index 77b405508743..3e961dc39634 100644
> > --- a/kernel/dma/Kconfig
> > +++ b/kernel/dma/Kconfig
> > @@ -80,6 +80,20 @@ config SWIOTLB
> >       bool
> >       select NEED_DMA_MAP_STATE
> >
> > +config DMA_RESTRICTED_POOL
> > +     bool "DMA Restricted Pool"
> > +     depends on OF && OF_RESERVED_MEM
> > +     select SWIOTLB
>
> This makes SWIOTLB user configurable, which in turn results in
>
> mips64-linux-ld: arch/mips/kernel/setup.o: in function `arch_mem_init':
> setup.c:(.init.text+0x19c8): undefined reference to `plat_swiotlb_setup'
> make[1]: *** [Makefile:1280: vmlinux] Error 1
>
> when building mips:allmodconfig.
>
> Should this possibly be "depends on SWIOTLB" ?

Patch is sent here: https://lkml.org/lkml/2021/8/26/932

>
> Thanks,
> Guenter

Thanks,
Claire