Re: [PATCH 13/14] dma-direct: handle force decryption for dma coherent buffers in common code

[Tom Lendacky]

On 3/19/2018 5:38 AM, Christoph Hellwig wrote:
> With that in place the generic dma-direct routines can be used to
> allocate non-encrypted bounce buffers, and the x86 SEV case can use
> the generic swiotlb ops including nice features such as using CMA
> allocations.
> 
> Note that I'm not too happy about using sev_active() in dma-direct, but
> I couldn't come up with a good enough name for a wrapper to make it
> worth adding.
> 
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>

Reviewed-by: Tom Lendacky <thomas.lendacky@xxxxxxx>

> ---
>  arch/x86/mm/mem_encrypt.c | 73 ++---------------------------------------------
>  lib/dma-direct.c          | 32 +++++++++++++++++----
>  2 files changed, 29 insertions(+), 76 deletions(-)
> 
> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> index 1a05bea831a8..65f45e0ef496 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -200,58 +200,6 @@ void __init sme_early_init(void)
>  		swiotlb_force = SWIOTLB_FORCE;
>  }
>  
> -static void *sev_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
> -		       gfp_t gfp, unsigned long attrs)
> -{
> -	unsigned int order;
> -	struct page *page;
> -	void *vaddr = NULL;
> -
> -	order = get_order(size);
> -	page = alloc_pages_node(dev_to_node(dev), gfp, order);
> -	if (page) {
> -		dma_addr_t addr;
> -
> -		/*
> -		 * Since we will be clearing the encryption bit, check the
> -		 * mask with it already cleared.
> -		 */
> -		addr = __phys_to_dma(dev, page_to_phys(page));
> -		if ((addr + size) > dev->coherent_dma_mask) {
> -			__free_pages(page, get_order(size));
> -		} else {
> -			vaddr = page_address(page);
> -			*dma_handle = addr;
> -		}
> -	}
> -
> -	if (!vaddr)
> -		vaddr = swiotlb_alloc_coherent(dev, size, dma_handle, gfp);
> -
> -	if (!vaddr)
> -		return NULL;
> -
> -	/* Clear the SME encryption bit for DMA use if not swiotlb area */
> -	if (!is_swiotlb_buffer(dma_to_phys(dev, *dma_handle))) {
> -		set_memory_decrypted((unsigned long)vaddr, 1 << order);
> -		memset(vaddr, 0, PAGE_SIZE << order);
> -		*dma_handle = __sme_clr(*dma_handle);
> -	}
> -
> -	return vaddr;
> -}
> -
> -static void sev_free(struct device *dev, size_t size, void *vaddr,
> -		     dma_addr_t dma_handle, unsigned long attrs)
> -{
> -	/* Set the SME encryption bit for re-use if not swiotlb area */
> -	if (!is_swiotlb_buffer(dma_to_phys(dev, dma_handle)))
> -		set_memory_encrypted((unsigned long)vaddr,
> -				     1 << get_order(size));
> -
> -	swiotlb_free_coherent(dev, size, vaddr, dma_handle);
> -}
> -
>  static void __init __set_clr_pte_enc(pte_t *kpte, int level, bool enc)
>  {
>  	pgprot_t old_prot, new_prot;
> @@ -404,20 +352,6 @@ bool sev_active(void)
>  }
>  EXPORT_SYMBOL(sev_active);
>  
> -static const struct dma_map_ops sev_dma_ops = {
> -	.alloc                  = sev_alloc,
> -	.free                   = sev_free,
> -	.map_page               = swiotlb_map_page,
> -	.unmap_page             = swiotlb_unmap_page,
> -	.map_sg                 = swiotlb_map_sg_attrs,
> -	.unmap_sg               = swiotlb_unmap_sg_attrs,
> -	.sync_single_for_cpu    = swiotlb_sync_single_for_cpu,
> -	.sync_single_for_device = swiotlb_sync_single_for_device,
> -	.sync_sg_for_cpu        = swiotlb_sync_sg_for_cpu,
> -	.sync_sg_for_device     = swiotlb_sync_sg_for_device,
> -	.mapping_error          = swiotlb_dma_mapping_error,
> -};
> -
>  /* Architecture __weak replacement functions */
>  void __init mem_encrypt_init(void)
>  {
> @@ -428,12 +362,11 @@ void __init mem_encrypt_init(void)
>  	swiotlb_update_mem_attributes();
>  
>  	/*
> -	 * With SEV, DMA operations cannot use encryption. New DMA ops
> -	 * are required in order to mark the DMA areas as decrypted or
> -	 * to use bounce buffers.
> +	 * With SEV, DMA operations cannot use encryption, we need to use
> +	 * SWIOTLB to bounce buffer DMA operation.
>  	 */
>  	if (sev_active())
> -		dma_ops = &sev_dma_ops;
> +		dma_ops = &swiotlb_dma_ops;
>  
>  	/*
>  	 * With SEV, we need to unroll the rep string I/O instructions.
> diff --git a/lib/dma-direct.c b/lib/dma-direct.c
> index c9e8e21cb334..1277d293d4da 100644
> --- a/lib/dma-direct.c
> +++ b/lib/dma-direct.c
> @@ -9,6 +9,7 @@
>  #include <linux/scatterlist.h>
>  #include <linux/dma-contiguous.h>
>  #include <linux/pfn.h>
> +#include <linux/set_memory.h>
>  
>  #define DIRECT_MAPPING_ERROR		0
>  
> @@ -20,6 +21,14 @@
>  #define ARCH_ZONE_DMA_BITS 24
>  #endif
>  
> +/*
> + * For AMD SEV all DMA must be to unencrypted addresses.
> + */
> +static inline bool force_dma_unencrypted(void)
> +{
> +	return sev_active();
> +}
> +
>  static bool
>  check_addr(struct device *dev, dma_addr_t dma_addr, size_t size,
>  		const char *caller)
> @@ -37,7 +46,9 @@ check_addr(struct device *dev, dma_addr_t dma_addr, size_t size,
>  
>  static bool dma_coherent_ok(struct device *dev, phys_addr_t phys, size_t size)
>  {
> -	return phys_to_dma(dev, phys) + size - 1 <= dev->coherent_dma_mask;
> +	dma_addr_t addr = force_dma_unencrypted() ?
> +		__phys_to_dma(dev, phys) : phys_to_dma(dev, phys);
> +	return addr + size - 1 <= dev->coherent_dma_mask;
>  }
>  
>  void *dma_direct_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
> @@ -46,6 +57,7 @@ void *dma_direct_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
>  	unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
>  	int page_order = get_order(size);
>  	struct page *page = NULL;
> +	void *ret;
>  
>  	/* GFP_DMA32 and GFP_DMA are no ops without the corresponding zones: */
>  	if (dev->coherent_dma_mask <= DMA_BIT_MASK(ARCH_ZONE_DMA_BITS))
> @@ -78,10 +90,15 @@ void *dma_direct_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
>  
>  	if (!page)
>  		return NULL;
> -
> -	*dma_handle = phys_to_dma(dev, page_to_phys(page));
> -	memset(page_address(page), 0, size);
> -	return page_address(page);
> +	ret = page_address(page);
> +	if (force_dma_unencrypted()) {
> +		set_memory_decrypted((unsigned long)ret, 1 << page_order);
> +		*dma_handle = __phys_to_dma(dev, page_to_phys(page));
> +	} else {
> +		*dma_handle = phys_to_dma(dev, page_to_phys(page));
> +	}
> +	memset(ret, 0, size);
> +	return ret;
>  }
>  
>  /*
> @@ -92,9 +109,12 @@ void dma_direct_free(struct device *dev, size_t size, void *cpu_addr,
>  		dma_addr_t dma_addr, unsigned long attrs)
>  {
>  	unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> +	unsigned int page_order = get_order(size);
>  
> +	if (force_dma_unencrypted())
> +		set_memory_encrypted((unsigned long)cpu_addr, 1 << page_order);
>  	if (!dma_release_from_contiguous(dev, virt_to_page(cpu_addr), count))
> -		free_pages((unsigned long)cpu_addr, get_order(size));
> +		free_pages((unsigned long)cpu_addr, page_order);
>  }
>  
>  static dma_addr_t dma_direct_map_page(struct device *dev, struct page *page,
>