Re: [PATCH v5 23/32] swiotlb: Add warnings for use of bounce buffers with SME

[Borislav Petkov]

On Tue, Apr 18, 2017 at 04:20:19PM -0500, Tom Lendacky wrote:
> Add warnings to let the user know when bounce buffers are being used for
> DMA when SME is active.  Since the bounce buffers are not in encrypted
> memory, these notifications are to allow the user to determine some
> appropriate action - if necessary.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
> ---
>  arch/x86/include/asm/mem_encrypt.h |   11 +++++++++++
>  include/linux/dma-mapping.h        |   11 +++++++++++
>  include/linux/mem_encrypt.h        |    6 ++++++
>  lib/swiotlb.c                      |    3 +++
>  4 files changed, 31 insertions(+)
> 
> diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
> index 0637b4b..b406df2 100644
> --- a/arch/x86/include/asm/mem_encrypt.h
> +++ b/arch/x86/include/asm/mem_encrypt.h
> @@ -26,6 +26,11 @@ static inline bool sme_active(void)
>  	return !!sme_me_mask;
>  }
>  
> +static inline u64 sme_dma_mask(void)
> +{
> +	return ((u64)sme_me_mask << 1) - 1;
> +}
> +
>  void __init sme_early_encrypt(resource_size_t paddr,
>  			      unsigned long size);
>  void __init sme_early_decrypt(resource_size_t paddr,
> @@ -50,6 +55,12 @@ static inline bool sme_active(void)
>  {
>  	return false;
>  }
> +
> +static inline u64 sme_dma_mask(void)
> +{
> +	return 0ULL;
> +}
> +
>  #endif
>  
>  static inline void __init sme_early_encrypt(resource_size_t paddr,
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index 0977317..f825870 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -10,6 +10,7 @@
>  #include <linux/scatterlist.h>
>  #include <linux/kmemcheck.h>
>  #include <linux/bug.h>
> +#include <linux/mem_encrypt.h>
>  
>  /**
>   * List of possible attributes associated with a DMA mapping. The semantics
> @@ -577,6 +578,11 @@ static inline int dma_set_mask(struct device *dev, u64 mask)
>  
>  	if (!dev->dma_mask || !dma_supported(dev, mask))
>  		return -EIO;
> +
> +	if (sme_active() && (mask < sme_dma_mask()))
> +		dev_warn_ratelimited(dev,
> +				     "SME is active, device will require DMA bounce buffers\n");

Bah, no need to break that line - just let it stick out. Ditto for the
others.

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.