Subject: Re: [PATCH v6 06/20] dma: swiotlb: track pool encryption state and honor DMA_ATTR_CC_SHARED

From: Petr Tesarik <[email-masked]>
Date: Tue, 9 Jun 2026 14:48:36 +0200

On Thu,  4 Jun 2026 14:09:45 +0530
"Aneesh Kumar K.V (Arm)" <[email-masked]> wrote:

> Teach swiotlb to distinguish between encrypted and decrypted bounce
> buffer pools, and make allocation and mapping paths select a pool whose
> state matches the requested DMA attributes.
> 
> Add a unencrypted flag to io_tlb_mem, initialize it for the default and
> restricted pools, and propagate DMA_ATTR_CC_SHARED into swiotlb pool
> allocation. Reject swiotlb alloc/map requests when the selected pool does
> not match the required encrypted/decrypted state.
> 
> Also return DMA addresses with the matching phys_to_dma_{encrypted,
> unencrypted} helper so the DMA address encoding stays consistent with the
> chosen pool.
> 
> Tested-by: Jiri Pirko <[email-masked]>
> Tested-by: Michael Kelley <[email-masked]>
> Tested-by: Mostafa Saleh <[email-masked]>
> Signed-off-by: Aneesh Kumar K.V (Arm) <[email-masked]>
> ---
>  include/linux/dma-direct.h |  10 +++
>  include/linux/swiotlb.h    |   8 +-
>  kernel/dma/direct.c        |  13 +++-
>  kernel/dma/swiotlb.c       | 154 ++++++++++++++++++++++++++++---------
>  4 files changed, 142 insertions(+), 43 deletions(-)
> 
> diff --git a/include/linux/dma-direct.h b/include/linux/dma-direct.h
> index c249912456f9..94fad4e7c11e 100644
> --- a/include/linux/dma-direct.h
> +++ b/include/linux/dma-direct.h
> @@ -77,6 +77,10 @@ static inline dma_addr_t dma_range_map_max(const struct bus_dma_region *map)
>  #ifndef phys_to_dma_unencrypted
>  #define phys_to_dma_unencrypted		phys_to_dma
>  #endif
> +
> +#ifndef phys_to_dma_encrypted
> +#define phys_to_dma_encrypted		phys_to_dma
> +#endif
>  #else
>  static inline dma_addr_t __phys_to_dma(struct device *dev, phys_addr_t paddr)
>  {
> @@ -90,6 +94,12 @@ static inline dma_addr_t phys_to_dma_unencrypted(struct device *dev,
>  {
>  	return dma_addr_unencrypted(__phys_to_dma(dev, paddr));
>  }
> +
> +static inline dma_addr_t phys_to_dma_encrypted(struct device *dev,
> +		phys_addr_t paddr)
> +{
> +	return dma_addr_encrypted(__phys_to_dma(dev, paddr));
> +}
>  /*
>   * If memory encryption is supported, phys_to_dma will set the memory encryption
>   * bit in the DMA address, and dma_to_phys will clear it.
> diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
> index 29187cec90d8..4dcbf3931be1 100644
> --- a/include/linux/swiotlb.h
> +++ b/include/linux/swiotlb.h
> @@ -81,6 +81,7 @@ struct io_tlb_pool {
>  	struct list_head node;
>  	struct rcu_head rcu;
>  	bool transient;
> +	bool unencrypted;

IIUC this is a copy of the unencrypted member in the corresponding
struct io_tlb_mem. In other words, if pools are allocated dynamically,
all pools must have the same encryption state, correct?

>  #endif
>  };
>  
> @@ -111,6 +112,7 @@ struct io_tlb_mem {
>  	struct dentry *debugfs;
>  	bool force_bounce;
>  	bool for_alloc;
> +	bool unencrypted;
>  #ifdef CONFIG_SWIOTLB_DYNAMIC
>  	bool can_grow;
>  	u64 phys_limit;
> @@ -282,7 +284,8 @@ static inline void swiotlb_sync_single_for_cpu(struct device *dev,
>  extern void swiotlb_print_info(void);
>  
>  #ifdef CONFIG_DMA_RESTRICTED_POOL
> -struct page *swiotlb_alloc(struct device *dev, size_t size);
> +struct page *swiotlb_alloc(struct device *dev, size_t size,
> +		unsigned long attrs);
>  bool swiotlb_free(struct device *dev, struct page *page, size_t size);
>  void swiotlb_free_from_pool(struct device *dev, phys_addr_t tlb_addr,
>  		size_t size, struct io_tlb_pool *pool);
> @@ -292,7 +295,8 @@ static inline bool is_swiotlb_for_alloc(struct device *dev)
>  	return dev->dma_io_tlb_mem->for_alloc;
>  }
>  #else
> -static inline struct page *swiotlb_alloc(struct device *dev, size_t size)
> +static inline struct page *swiotlb_alloc(struct device *dev, size_t size,
> +		unsigned long attrs)
>  {
>  	return NULL;
>  }
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index 681f16a984ab..0b4a26c6b6fd 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -96,9 +96,10 @@ static int dma_set_encrypted(struct device *dev, void *vaddr, size_t size)
>  	return ret;
>  }
>  
> -static struct page *dma_direct_alloc_swiotlb(struct device *dev, size_t size)
> +static struct page *dma_direct_alloc_swiotlb(struct device *dev, size_t size,
> +		unsigned long attrs)
>  {
> -	struct page *page = swiotlb_alloc(dev, size);
> +	struct page *page = swiotlb_alloc(dev, size, attrs);
>  
>  	if (page && !dma_coherent_ok(dev, page_to_phys(page), size)) {
>  		swiotlb_free(dev, page, size);
> @@ -258,8 +259,12 @@ void *dma_direct_alloc(struct device *dev, size_t size,
>  						  gfp, attrs);
>  
>  	if (is_swiotlb_for_alloc(dev)) {
> -		page = dma_direct_alloc_swiotlb(dev, size);
> +		page = dma_direct_alloc_swiotlb(dev, size, attrs);
>  		if (page) {
> +			/*
> +			 * swiotlb allocations comes from pool already marked
> +			 * decrypted
> +			 */
>  			mark_mem_decrypt = false;
>  			goto setup_page;
>  		}
> @@ -407,7 +412,7 @@ struct page *dma_direct_alloc_pages(struct device *dev, size_t size,
>  						  gfp, attrs);
>  
>  	if (is_swiotlb_for_alloc(dev)) {
> -		page = dma_direct_alloc_swiotlb(dev, size);
> +		page = dma_direct_alloc_swiotlb(dev, size, attrs);
>  		if (!page)
>  			return NULL;
>  
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index 78ce05857c00..2bf3981db35d 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -259,10 +259,21 @@ void __init swiotlb_update_mem_attributes(void)
>  	struct io_tlb_pool *mem = &io_tlb_default_mem.defpool;
>  	unsigned long bytes;
>  
> +	/*
> +	 * if platform support memory encryption, swiotlb buffers are
> +	 * decrypted by default.
> +	 */
> +	if (cc_platform_has(CC_ATTR_MEM_ENCRYPT))
> +		io_tlb_default_mem.unencrypted = true;
> +	else
> +		io_tlb_default_mem.unencrypted = false;
> +
>  	if (!mem->nslabs || mem->late_alloc)
>  		return;
>  	bytes = PAGE_ALIGN(mem->nslabs << IO_TLB_SHIFT);
> -	set_memory_decrypted((unsigned long)mem->vaddr, bytes >> PAGE_SHIFT);
> +
> +	if (io_tlb_default_mem.unencrypted)
> +		set_memory_decrypted((unsigned long)mem->vaddr, bytes >> PAGE_SHIFT);
>  }
>  
>  static void swiotlb_init_io_tlb_pool(struct io_tlb_pool *mem, phys_addr_t start,
> @@ -505,8 +516,10 @@ int swiotlb_init_late(size_t size, gfp_t gfp_mask,
>  	if (!mem->slots)
>  		goto error_slots;
>  
> -	set_memory_decrypted((unsigned long)vstart,
> -			     (nslabs << IO_TLB_SHIFT) >> PAGE_SHIFT);
> +	if (io_tlb_default_mem.unencrypted)
> +		set_memory_decrypted((unsigned long)vstart,
> +				     (nslabs << IO_TLB_SHIFT) >> PAGE_SHIFT);
> +
>  	swiotlb_init_io_tlb_pool(mem, virt_to_phys(vstart), nslabs, true,
>  				 nareas);
>  	add_mem_pool(&io_tlb_default_mem, mem);
> @@ -539,7 +552,9 @@ void __init swiotlb_exit(void)
>  	tbl_size = PAGE_ALIGN(mem->end - mem->start);
>  	slots_size = PAGE_ALIGN(array_size(sizeof(*mem->slots), mem->nslabs));
>  
> -	set_memory_encrypted(tbl_vaddr, tbl_size >> PAGE_SHIFT);
> +	if (io_tlb_default_mem.unencrypted)
> +		set_memory_encrypted(tbl_vaddr, tbl_size >> PAGE_SHIFT);
> +
>  	if (mem->late_alloc) {
>  		area_order = get_order(array_size(sizeof(*mem->areas),
>  			mem->nareas));
> @@ -563,6 +578,7 @@ void __init swiotlb_exit(void)
>   * @gfp:	GFP flags for the allocation.
>   * @bytes:	Size of the buffer.
>   * @phys_limit:	Maximum allowed physical address of the buffer.
> + * @unencrypted: true to allocate unencrypted memory, false for encrypted memory
>   *
>   * Allocate pages from the buddy allocator. If successful, make the allocated
>   * pages decrypted that they can be used for DMA.
> @@ -570,7 +586,8 @@ void __init swiotlb_exit(void)
>   * Return: Decrypted pages, %NULL on allocation failure, or ERR_PTR(-EAGAIN)
>   * if the allocated physical address was above @phys_limit.
>   */
> -static struct page *alloc_dma_pages(gfp_t gfp, size_t bytes, u64 phys_limit)
> +static struct page *alloc_dma_pages(gfp_t gfp, size_t bytes,
> +		u64 phys_limit, bool unencrypted)
>  {
>  	unsigned int order = get_order(bytes);
>  	struct page *page;
> @@ -588,13 +605,13 @@ static struct page *alloc_dma_pages(gfp_t gfp, size_t bytes, u64 phys_limit)
>  	}
>  
>  	vaddr = phys_to_virt(paddr);
> -	if (set_memory_decrypted((unsigned long)vaddr, PFN_UP(bytes)))
> +	if (unencrypted && set_memory_decrypted((unsigned long)vaddr, PFN_UP(bytes)))
>  		goto error;
>  	return page;
>  
>  error:
>  	/* Intentional leak if pages cannot be encrypted again. */
> -	if (!set_memory_encrypted((unsigned long)vaddr, PFN_UP(bytes)))
> +	if (unencrypted && !set_memory_encrypted((unsigned long)vaddr, PFN_UP(bytes)))
>  		__free_pages(page, order);
>  	return NULL;
>  }
> @@ -604,30 +621,26 @@ static struct page *alloc_dma_pages(gfp_t gfp, size_t bytes, u64 phys_limit)
>   * @dev:	Device for which a memory pool is allocated.
>   * @bytes:	Size of the buffer.
>   * @phys_limit:	Maximum allowed physical address of the buffer.
> + * @attrs:	DMA attributes for the allocation.
>   * @gfp:	GFP flags for the allocation.
>   *
>   * Return: Allocated pages, or %NULL on allocation failure.
>   */
>  static struct page *swiotlb_alloc_tlb(struct device *dev, size_t bytes,
> -		u64 phys_limit, gfp_t gfp)
> +		u64 phys_limit, unsigned long attrs, gfp_t gfp)

If my assumption above is correct, then I prefer to add a struct
io_tlb_mem *mem parameter here and calculate the allocation attributes
inside this function, so you don't have to repeat it in the callers.

>  {
>  	struct page *page;
> -	unsigned long attrs = 0;
>  
>  	/*
>  	 * Allocate from the atomic pools if memory is encrypted and
>  	 * the allocation is atomic, because decrypting may block.
>  	 */
> -	if (!gfpflags_allow_blocking(gfp) && dev && force_dma_unencrypted(dev)) {
> +	if (!gfpflags_allow_blocking(gfp) && (attrs & DMA_ATTR_CC_SHARED)) {

You're removing the check that dev is non-NULL. This is fine, because
the only call with dev == NULL is from swiotlb_dyn_alloc(), and that one
uses GFP_KERNEL (i.e. allows blocking). However, if this is an intended
optimization, I'd rather have it in a separate commit, with this
explanation why it's OK to do it.

The rest of the patch looks good to me.

Petr T

>  		void *vaddr;
>  
>  		if (!IS_ENABLED(CONFIG_DMA_COHERENT_POOL))
>  			return NULL;
>  
> -		/* swiotlb considered decrypted by default */
> -		if (cc_platform_has(CC_ATTR_MEM_ENCRYPT))
> -			attrs = DMA_ATTR_CC_SHARED;
> -
>  		return dma_alloc_from_pool(dev, bytes, &vaddr, gfp,
>  					   attrs, dma_coherent_ok);
>  	}
> @@ -638,7 +651,8 @@ static struct page *swiotlb_alloc_tlb(struct device *dev, size_t bytes,
>  	else if (phys_limit <= DMA_BIT_MASK(32))
>  		gfp |= __GFP_DMA32;
>  
> -	while (IS_ERR(page = alloc_dma_pages(gfp, bytes, phys_limit))) {
> +	while (IS_ERR(page = alloc_dma_pages(gfp, bytes, phys_limit,
> +					     !!(attrs & DMA_ATTR_CC_SHARED)))) {
>  		if (IS_ENABLED(CONFIG_ZONE_DMA32) &&
>  		    phys_limit < DMA_BIT_MASK(64) &&
>  		    !(gfp & (__GFP_DMA32 | __GFP_DMA)))
> @@ -657,15 +671,18 @@ static struct page *swiotlb_alloc_tlb(struct device *dev, size_t bytes,
>   * swiotlb_free_tlb() - free a dynamically allocated IO TLB buffer
>   * @vaddr:	Virtual address of the buffer.
>   * @bytes:	Size of the buffer.
> + * @unencrypted: true if @vaddr was allocated decrypted and must be
> + *	re-encrypted before being freed
>   */
> -static void swiotlb_free_tlb(void *vaddr, size_t bytes)
> +static void swiotlb_free_tlb(void *vaddr, size_t bytes, bool unencrypted)
>  {
>  	if (IS_ENABLED(CONFIG_DMA_COHERENT_POOL) &&
>  	    dma_free_from_pool(NULL, vaddr, bytes))
>  		return;
>  
>  	/* Intentional leak if pages cannot be encrypted again. */
> -	if (!set_memory_encrypted((unsigned long)vaddr, PFN_UP(bytes)))
> +	if (!unencrypted ||
> +	    !set_memory_encrypted((unsigned long)vaddr, PFN_UP(bytes)))
>  		__free_pages(virt_to_page(vaddr), get_order(bytes));
>  }
>  
> @@ -676,6 +693,7 @@ static void swiotlb_free_tlb(void *vaddr, size_t bytes)
>   * @nslabs:	Desired (maximum) number of slabs.
>   * @nareas:	Number of areas.
>   * @phys_limit:	Maximum DMA buffer physical address.
> + * @attrs:	DMA attributes for the allocation.
>   * @gfp:	GFP flags for the allocations.
>   *
>   * Allocate and initialize a new IO TLB memory pool. The actual number of
> @@ -686,7 +704,8 @@ static void swiotlb_free_tlb(void *vaddr, size_t bytes)
>   */
>  static struct io_tlb_pool *swiotlb_alloc_pool(struct device *dev,
>  		unsigned long minslabs, unsigned long nslabs,
> -		unsigned int nareas, u64 phys_limit, gfp_t gfp)
> +		unsigned int nareas, u64 phys_limit,
> +		unsigned long attrs, gfp_t gfp)
>  {
>  	struct io_tlb_pool *pool;
>  	unsigned int slot_order;
> @@ -704,9 +723,10 @@ static struct io_tlb_pool *swiotlb_alloc_pool(struct device *dev,
>  	if (!pool)
>  		goto error;
>  	pool->areas = (void *)pool + sizeof(*pool);
> +	pool->unencrypted = !!(attrs & DMA_ATTR_CC_SHARED);
>  
>  	tlb_size = nslabs << IO_TLB_SHIFT;
> -	while (!(tlb = swiotlb_alloc_tlb(dev, tlb_size, phys_limit, gfp))) {
> +	while (!(tlb = swiotlb_alloc_tlb(dev, tlb_size, phys_limit, attrs, gfp))) {
>  		if (nslabs <= minslabs)
>  			goto error_tlb;
>  		nslabs = ALIGN(nslabs >> 1, IO_TLB_SEGSIZE);
> @@ -724,7 +744,8 @@ static struct io_tlb_pool *swiotlb_alloc_pool(struct device *dev,
>  	return pool;
>  
>  error_slots:
> -	swiotlb_free_tlb(page_address(tlb), tlb_size);
> +	swiotlb_free_tlb(page_address(tlb), tlb_size,
> +			 !!(attrs & DMA_ATTR_CC_SHARED));
>  error_tlb:
>  	kfree(pool);
>  error:
> @@ -742,7 +763,9 @@ static void swiotlb_dyn_alloc(struct work_struct *work)
>  	struct io_tlb_pool *pool;
>  
>  	pool = swiotlb_alloc_pool(NULL, IO_TLB_MIN_SLABS, default_nslabs,
> -				  default_nareas, mem->phys_limit, GFP_KERNEL);
> +				  default_nareas, mem->phys_limit,
> +				  mem->unencrypted ? DMA_ATTR_CC_SHARED : 0,
> +				  GFP_KERNEL);
>  	if (!pool) {
>  		pr_warn_ratelimited("Failed to allocate new pool");
>  		return;
> @@ -762,7 +785,7 @@ static void swiotlb_dyn_free(struct rcu_head *rcu)
>  	size_t tlb_size = pool->end - pool->start;
>  
>  	free_pages((unsigned long)pool->slots, get_order(slots_size));
> -	swiotlb_free_tlb(pool->vaddr, tlb_size);
> +	swiotlb_free_tlb(pool->vaddr, tlb_size, pool->unencrypted);
>  	kfree(pool);
>  }
>  
> @@ -1037,13 +1060,11 @@ static void dec_transient_used(struct io_tlb_mem *mem, unsigned int nslots)
>   * Return: Index of the first allocated slot, or -1 on error.
>   */
>  static int swiotlb_search_pool_area(struct device *dev, struct io_tlb_pool *pool,
> -		int area_index, phys_addr_t orig_addr, size_t alloc_size,
> -		unsigned int alloc_align_mask)
> +		int area_index, phys_addr_t orig_addr, dma_addr_t tbl_dma_addr,
> +		size_t alloc_size, unsigned int alloc_align_mask)
>  {
>  	struct io_tlb_area *area = pool->areas + area_index;
>  	unsigned long boundary_mask = dma_get_seg_boundary(dev);
> -	dma_addr_t tbl_dma_addr =
> -		phys_to_dma_unencrypted(dev, pool->start) & boundary_mask;
>  	unsigned long max_slots = get_max_slots(boundary_mask);
>  	unsigned int iotlb_align_mask = dma_get_min_align_mask(dev);
>  	unsigned int nslots = nr_slots(alloc_size), stride;
> @@ -1056,6 +1077,8 @@ static int swiotlb_search_pool_area(struct device *dev, struct io_tlb_pool *pool
>  	BUG_ON(!nslots);
>  	BUG_ON(area_index >= pool->nareas);
>  
> +	tbl_dma_addr &= boundary_mask;
> +
>  	/*
>  	 * Historically, swiotlb allocations >= PAGE_SIZE were guaranteed to be
>  	 * page-aligned in the absence of any other alignment requirements.
> @@ -1167,6 +1190,7 @@ static int swiotlb_search_area(struct device *dev, int start_cpu,
>  {
>  	struct io_tlb_mem *mem = dev->dma_io_tlb_mem;
>  	struct io_tlb_pool *pool;
> +	dma_addr_t tbl_dma_addr;
>  	int area_index;
>  	int index = -1;
>  
> @@ -1175,9 +1199,15 @@ static int swiotlb_search_area(struct device *dev, int start_cpu,
>  		if (cpu_offset >= pool->nareas)
>  			continue;
>  		area_index = (start_cpu + cpu_offset) & (pool->nareas - 1);
> +
> +		if (mem->unencrypted)
> +			tbl_dma_addr = phys_to_dma_unencrypted(dev, pool->start);
> +		else
> +			tbl_dma_addr = phys_to_dma_encrypted(dev, pool->start);
> +
>  		index = swiotlb_search_pool_area(dev, pool, area_index,
> -						 orig_addr, alloc_size,
> -						 alloc_align_mask);
> +						 orig_addr, tbl_dma_addr,
> +						 alloc_size, alloc_align_mask);
>  		if (index >= 0) {
>  			*retpool = pool;
>  			break;
> @@ -1207,6 +1237,7 @@ static int swiotlb_find_slots(struct device *dev, phys_addr_t orig_addr,
>  {
>  	struct io_tlb_mem *mem = dev->dma_io_tlb_mem;
>  	struct io_tlb_pool *pool;
> +	dma_addr_t tbl_dma_addr;
>  	unsigned long nslabs;
>  	unsigned long flags;
>  	u64 phys_limit;
> @@ -1232,11 +1263,17 @@ static int swiotlb_find_slots(struct device *dev, phys_addr_t orig_addr,
>  	nslabs = nr_slots(alloc_size);
>  	phys_limit = min_not_zero(*dev->dma_mask, dev->bus_dma_limit);
>  	pool = swiotlb_alloc_pool(dev, nslabs, nslabs, 1, phys_limit,
> +				  mem->unencrypted ? DMA_ATTR_CC_SHARED : 0,
>  				  GFP_NOWAIT);
>  	if (!pool)
>  		return -1;
>  
> -	index = swiotlb_search_pool_area(dev, pool, 0, orig_addr,
> +	if (mem->unencrypted)
> +		tbl_dma_addr = phys_to_dma_unencrypted(dev, pool->start);
> +	else
> +		tbl_dma_addr = phys_to_dma_encrypted(dev, pool->start);
> +
> +	index = swiotlb_search_pool_area(dev, pool, 0, orig_addr, tbl_dma_addr,
>  					 alloc_size, alloc_align_mask);
>  	if (index < 0) {
>  		swiotlb_dyn_free(&pool->rcu);
> @@ -1281,15 +1318,23 @@ static int swiotlb_find_slots(struct device *dev, phys_addr_t orig_addr,
>  		size_t alloc_size, unsigned int alloc_align_mask,
>  		struct io_tlb_pool **retpool)
>  {
> +	struct io_tlb_mem *mem = dev->dma_io_tlb_mem;
>  	struct io_tlb_pool *pool;
> +	dma_addr_t tbl_dma_addr;
>  	int start, i;
>  	int index;
>  
> -	*retpool = pool = &dev->dma_io_tlb_mem->defpool;
> +	*retpool = pool = &mem->defpool;
> +	if (mem->unencrypted)
> +		tbl_dma_addr = phys_to_dma_unencrypted(dev, pool->start);
> +	else
> +		tbl_dma_addr = phys_to_dma_encrypted(dev, pool->start);
> +
>  	i = start = raw_smp_processor_id() & (pool->nareas - 1);
>  	do {
>  		index = swiotlb_search_pool_area(dev, pool, i, orig_addr,
> -						 alloc_size, alloc_align_mask);
> +						 tbl_dma_addr, alloc_size,
> +						 alloc_align_mask);
>  		if (index >= 0)
>  			return index;
>  		if (++i >= pool->nareas)
> @@ -1372,9 +1417,19 @@ static unsigned long mem_used(struct io_tlb_mem *mem)
>   *			any pre- or post-padding for alignment
>   * @alloc_align_mask:	Required start and end alignment of the allocated buffer
>   * @dir:		DMA direction
> - * @attrs:		Optional DMA attributes for the map operation
> + * @attrs:		Optional DMA attributes for the map operation, updated
> + *			to match the selected SWIOTLB pool
>   *
>   * Find and allocate a suitable sequence of IO TLB slots for the request.
> + * The device's SWIOTLB pool must match the device's current DMA encryption
> + * requirements. If the device requires decrypted DMA, bouncing is done through
> + * an unencrypted pool and the mapping is marked shared. If the device can DMA
> + * to encrypted memory, bouncing is done through an encrypted pool even when the
> + * original DMA address was unencrypted. Enabling encrypted DMA for a device is
> + * therefore expected to update its default io_tlb_mem to an encrypted pool, so
> + * later bounce mappings for both encrypted and decrypted original memory use
> + * that encrypted pool.
> + *
>   * The allocated space starts at an alignment specified by alloc_align_mask,
>   * and the size of the allocated space is rounded up so that the total amount
>   * of allocated space is a multiple of (alloc_align_mask + 1). If
> @@ -1411,6 +1466,16 @@ phys_addr_t swiotlb_tbl_map_single(struct device *dev, phys_addr_t orig_addr,
>  	if (cc_platform_has(CC_ATTR_MEM_ENCRYPT))
>  		pr_warn_once("Memory encryption is active and system is using DMA bounce buffers\n");
>  
> +	/* swiotlb pool is incorrect for this device */
> +	if (unlikely(mem->unencrypted != force_dma_unencrypted(dev)))
> +		return (phys_addr_t)DMA_MAPPING_ERROR;
> +
> +	/* Force attrs to match the kind of memory in the pool */
> +	if (mem->unencrypted)
> +		*attrs |= DMA_ATTR_CC_SHARED;
> +	else
> +		*attrs &= ~DMA_ATTR_CC_SHARED;
> +
>  	/*
>  	 * The default swiotlb memory pool is allocated with PAGE_SIZE
>  	 * alignment. If a mapping is requested with larger alignment,
> @@ -1608,8 +1673,11 @@ dma_addr_t swiotlb_map(struct device *dev, phys_addr_t paddr, size_t size,
>  	if (swiotlb_addr == (phys_addr_t)DMA_MAPPING_ERROR)
>  		return DMA_MAPPING_ERROR;
>  
> -	/* Ensure that the address returned is DMA'ble */
> -	dma_addr = phys_to_dma_unencrypted(dev, swiotlb_addr);
> +	if (attrs & DMA_ATTR_CC_SHARED)
> +		dma_addr = phys_to_dma_unencrypted(dev, swiotlb_addr);
> +	else
> +		dma_addr = phys_to_dma_encrypted(dev, swiotlb_addr);
> +
>  	if (unlikely(!dma_capable(dev, dma_addr, size, true))) {
>  		__swiotlb_tbl_unmap_single(dev, swiotlb_addr, size, dir,
>  			attrs | DMA_ATTR_SKIP_CPU_SYNC,
> @@ -1773,7 +1841,7 @@ static inline void swiotlb_create_debugfs_files(struct io_tlb_mem *mem,
>  
>  #ifdef CONFIG_DMA_RESTRICTED_POOL
>  
> -struct page *swiotlb_alloc(struct device *dev, size_t size)
> +struct page *swiotlb_alloc(struct device *dev, size_t size, unsigned long attrs)
>  {
>  	struct io_tlb_mem *mem = dev->dma_io_tlb_mem;
>  	struct io_tlb_pool *pool;
> @@ -1784,6 +1852,9 @@ struct page *swiotlb_alloc(struct device *dev, size_t size)
>  	if (!mem)
>  		return NULL;
>  
> +	if (mem->unencrypted != !!(attrs & DMA_ATTR_CC_SHARED))
> +		return NULL;
> +
>  	align = (1 << (get_order(size) + PAGE_SHIFT)) - 1;
>  	index = swiotlb_find_slots(dev, 0, size, align, &pool);
>  	if (index == -1)
> @@ -1859,9 +1930,18 @@ static int rmem_swiotlb_device_init(struct reserved_mem *rmem,
>  			kfree(mem);
>  			return -ENOMEM;
>  		}
> +		/*
> +		 * if platform supports memory encryption,
> +		 * restricted mem pool is decrypted by default
> +		 */
> +		if (cc_platform_has(CC_ATTR_MEM_ENCRYPT)) {
> +			mem->unencrypted = true;
> +			set_memory_decrypted((unsigned long)phys_to_virt(rmem->base),
> +					     rmem->size >> PAGE_SHIFT);
> +		} else {
> +			mem->unencrypted = false;
> +		}
>  
> -		set_memory_decrypted((unsigned long)phys_to_virt(rmem->base),
> -				     rmem->size >> PAGE_SHIFT);
>  		swiotlb_init_io_tlb_pool(pool, rmem->base, nslabs,
>  					 false, nareas);
>  		mem->force_bounce = true;