Re: [RFC PATCH v1 13/18] x86: DMA support for memory encryption

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Tue, Apr 26, 2016 at 05:58:12PM -0500, Tom Lendacky wrote:
> Since DMA addresses will effectively look like 48-bit addresses when the
> memory encryption mask is set, SWIOTLB is needed if the DMA mask of the
> device performing the DMA does not support 48-bits. SWIOTLB will be
> initialized to create un-encrypted bounce buffers for use by these devices.
> 


I presume the sme_me_mask does not use the lower 48 bits?


..snip..
> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> index 7d56d1b..594dc65 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -12,6 +12,8 @@
>  
>  #include <linux/init.h>
>  #include <linux/mm.h>
> +#include <linux/dma-mapping.h>
> +#include <linux/swiotlb.h>
>  
>  #include <asm/mem_encrypt.h>
>  #include <asm/cacheflush.h>
> @@ -168,6 +170,25 @@ void __init sme_early_init(void)
>  }
>  
>  /* Architecture __weak replacement functions */
> +void __init mem_encrypt_init(void)
> +{
> +	if (!sme_me_mask)
> +		return;
> +
> +	/* Make SWIOTLB use an unencrypted DMA area */
> +	swiotlb_clear_encryption();
> +}
> +
> +unsigned long swiotlb_get_me_mask(void)
> +{
> +	return sme_me_mask;
> +}
> +
> +void swiotlb_set_mem_dec(void *vaddr, unsigned long size)
> +{
> +	sme_set_mem_dec(vaddr, size);
> +}
> +
>  void __init *efi_me_early_memremap(resource_size_t paddr,
>  				   unsigned long size)
>  {
> diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
> index 017fced..121b9de 100644
> --- a/include/linux/swiotlb.h
> +++ b/include/linux/swiotlb.h
> @@ -30,6 +30,7 @@ int swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose);
>  extern unsigned long swiotlb_nr_tbl(void);
>  unsigned long swiotlb_size_or_default(void);
>  extern int swiotlb_late_init_with_tbl(char *tlb, unsigned long nslabs);
> +extern void __init swiotlb_clear_encryption(void);
>  
>  /*
>   * Enumeration for sync targets
> diff --git a/init/main.c b/init/main.c
> index b3c6e36..1013d1c 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -458,6 +458,10 @@ void __init __weak thread_info_cache_init(void)
>  }
>  #endif
>  
> +void __init __weak mem_encrypt_init(void)
> +{
> +}
> +
>  /*
>   * Set up kernel memory allocators
>   */
> @@ -597,6 +601,8 @@ asmlinkage __visible void __init start_kernel(void)
>  	 */
>  	locking_selftest();
>  
> +	mem_encrypt_init();
> +
>  #ifdef CONFIG_BLK_DEV_INITRD
>  	if (initrd_start && !initrd_below_start_ok &&
>  	    page_to_pfn(virt_to_page((void *)initrd_start)) < min_low_pfn) {

What happens if devices use the bounce buffer before mem_encrypt_init()?

..snip..

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