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

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Date:   Tue, 24 Aug 2021 07:26:01 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Claire Chang <tientzu@...omium.org>
Cc:     Rob Herring <robh+dt@...nel.org>, mpe@...erman.id.au,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
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Subject: Re: [PATCH v15 10/12] swiotlb: Add restricted DMA pool initialization

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@...omium.org>
> Reviewed-by: Christoph Hellwig <hch@....de>
> Tested-by: Stefano Stabellini <sstabellini@...nel.org>
> Tested-by: Will Deacon <will@...nel.org>
> ---
>  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" ?

Thanks,
Guenter