On Thu, May 14, 2026 at 06:18:05PM +0530, Aneesh Kumar K.V wrote: > Mostafa Saleh <[email protected]> writes: > > > On Thu, May 14, 2026 at 11:24:42AM +0530, Aneesh Kumar K.V wrote: > >> Mostafa Saleh <[email protected]> writes: > >> > >> > On Tue, May 12, 2026 at 02:33:59PM +0530, Aneesh Kumar K.V (Arm) 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 decrypted 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. > >> >> > >> >> Signed-off-by: Aneesh Kumar K.V (Arm) <[email protected]> > >> >> --- > >> >> include/linux/dma-direct.h | 10 ++++ > >> >> include/linux/swiotlb.h | 8 ++- > >> >> kernel/dma/direct.c | 14 +++-- > >> >> kernel/dma/swiotlb.c | 108 +++++++++++++++++++++++++++---------- > >> >> 4 files changed, 107 insertions(+), 33 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 3dae0f592063..b3fa3c6e0169 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; > >> >> #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); > >> >> > >> >> static inline bool is_swiotlb_for_alloc(struct device *dev) > >> >> @@ -290,7 +293,8 @@ 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 dc2907439b3d..97ae4fa10521 100644 > >> >> --- a/kernel/dma/direct.c > >> >> +++ b/kernel/dma/direct.c > >> >> @@ -104,9 +104,10 @@ static void __dma_direct_free_pages(struct device > >> >> *dev, struct page *page, > >> >> dma_free_contiguous(dev, page, size); > >> >> } > >> >> > >> >> -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); > >> >> @@ -266,8 +267,12 @@ 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; > >> >> } > >> >> @@ -374,6 +379,7 @@ void dma_direct_free(struct device *dev, size_t > >> >> size, > >> >> return; > >> >> > >> >> if (swiotlb_find_pool(dev, dma_to_phys(dev, dma_addr))) > >> >> + /* Swiotlb doesn't need a page attribute update on free > >> >> */ > >> >> mark_mem_encrypted = false; > >> >> > >> >> if (is_vmalloc_addr(cpu_addr)) { > >> >> @@ -403,7 +409,7 @@ 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 ab4eccbaa076..065663be282c 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) > >> >> { > >> >> 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)) { > >> >> 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); > >> >> } > >> >> > >> >> @@ -1232,6 +1255,7 @@ 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; > >> >> @@ -1394,6 +1418,7 @@ phys_addr_t swiotlb_tbl_map_single(struct device > >> >> *dev, phys_addr_t orig_addr, > >> >> enum dma_data_direction dir, unsigned long attrs) > >> >> { > >> >> struct io_tlb_mem *mem = dev->dma_io_tlb_mem; > >> >> + bool require_decrypted = false; > >> >> unsigned int offset; > >> >> struct io_tlb_pool *pool; > >> >> unsigned int i; > >> >> @@ -1411,6 +1436,16 @@ 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"); > >> >> > >> >> + /* > >> >> + * if we are trying to swiotlb map a decrypted paddr or the > >> >> paddr is encrypted > >> >> + * but the device is forcing decryption, use decrypted > >> >> io_tlb_mem > >> >> + */ > >> >> + if ((attrs & DMA_ATTR_CC_SHARED) || force_dma_unencrypted(dev)) > >> >> + require_decrypted = true; > >> >> + > >> >> + if (require_decrypted != mem->unencrypted) > >> >> + return (phys_addr_t)DMA_MAPPING_ERROR; > >> >> + > >> >> /* > >> >> * The default swiotlb memory pool is allocated with PAGE_SIZE > >> >> * alignment. If a mapping is requested with larger alignment, > >> >> @@ -1608,8 +1643,14 @@ 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); > >> >> + /* > >> >> + * Use the allocated io_tlb_mem encryption type to determine > >> >> dma addr. > >> >> + */ > >> >> + if (dev->dma_io_tlb_mem->unencrypted) > >> >> + 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 +1814,8 @@ 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 +1826,9 @@ 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) > >> >> @@ -1853,9 +1898,18 @@ 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; > >> >> + } > >> > > >> > This breaks pKVM as it doesn’t set CC_ATTR_MEM_ENCRYPT, so all virtio > >> > traffic now fails. > >> > > >> > Also, by design, some drivers are clueless about bouncing, so > >> > I believe that the pool should have a way to control it’s property > >> > (encrypted or decrypted) and that takes priority over whatever > >> > attributes comes from allocation. > >> > And that brings us to the same point whether it’s better to return > >> > the memory along with it’s state or we pass the requested state. > >> > I think for other cases it’s fine for the device/DMA-API to dictate > >> > the attrs, but not in restricted-dma case, the firmware just knows > >> > better. > >> > > >> > >> Is it that the pKVM guest kernel does not have awareness of > >> encrypted/decrypted DMA allocations? Instead, the firmware attaches > >> hypervisor-shared pages to the device via restricted-dma-pool? The > >> kernel then has swiotlb->for_alloc = true, and hence all DMA allocations > >> go through the restricted-dma-pool? > > > > Yes. > > > >> > >> Given that pKVM supports pkvm_set_memory_encrypted() and > >> pkvm_set_memory_decrypted(), can we consider adding CC_ATTR_MEM_ENCRYPT > >> support to pKVM? It would also be good to investigate whether we can set > >> force_dma_unencrypted(dev) to true where needed. > > > > I was looking in to that, but it didn't work because > > force_dma_unencrypted() is broken with restricted-dma due to the > > double decryption issue, that's when I sent my first series [1] > > > > May be we should land some basic fixes for that path so we can > > convert pKVM, then we do the full rework. > > > > I will revive my old work and see if I can send a RFC. > > > > [1] https://lore.kernel.org/all/[email protected]/ > > > > With this series, can you check whether the only change needed is > something like the following? > > modified kernel/dma/swiotlb.c > @@ -1905,7 +1905,8 @@ static int rmem_swiotlb_device_init(struct reserved_mem > *rmem, > * if platform supports memory encryption, > * restricted mem pool is decrypted by default > */ > - if (cc_platform_has(CC_ATTR_MEM_ENCRYPT)) { > + //if (cc_platform_has(CC_ATTR_MEM_ENCRYPT)) { > + if (true) { > mem->unencrypted = true; > set_memory_decrypted((unsigned > long)phys_to_virt(rmem->base), > rmem->size >> PAGE_SHIFT);
Yes, that boots, but I will need to do more tests. > > > > >> > >> I agree that this patch, as it stands, can break pKVM because we are now > >> missing the set_memory_decrypted() call required for pKVM to work. > >> > >> We now mark the swiotlb io_tlb_mem as unencrypted/encrypted in the guest > >> using struct io_tlb_mem->unencrypted. I am not clear what we can use for > >> pKVM to conditionalize this so that it works for both protected and > >> unprotected guests. > > > > There is no problem with non-protected guests as they don't use memory > > encryption, my initial thought was that th encrpyted/decrypted is > > per-pool property which is decided by FW (device-tree). > > > > What I meant was that we need a generic way to identify a pKVM guest, so > that we can use it in the conditional above. I have this patch, with that I can boot with your series unmodified, but I will need to do more testing. >From d795b4c4ee2437587616b2b342e9996afe6d6680 Mon Sep 17 00:00:00 2001 From: Mostafa Saleh <[email protected]> Date: Thu, 14 May 2026 13:46:15 +0000 Subject: [PATCH] arm64/coco: Add pKVM as a CC platform pKVM does support memory encryption, expose that to the rest of the kernel through cc_platform_has() At the moment, all devices inside the guest are emulated which requires its memory to be shared back to the host (decrypted), so set force_dma_unencrypted() to always return true. Signed-off-by: Mostafa Saleh <[email protected]> --- arch/arm64/include/asm/hypervisor.h | 6 ++++++ arch/arm64/include/asm/mem_encrypt.h | 3 ++- arch/arm64/kernel/rsi.c | 12 ------------ arch/arm64/mm/init.c | 13 +++++++++++++ drivers/virt/coco/pkvm-guest/arm-pkvm-guest.c | 5 +++++ 5 files changed, 26 insertions(+), 13 deletions(-) diff --git a/arch/arm64/include/asm/hypervisor.h b/arch/arm64/include/asm/hypervisor.h index a12fd897c877..1b0e15f290be 100644 --- a/arch/arm64/include/asm/hypervisor.h +++ b/arch/arm64/include/asm/hypervisor.h @@ -10,8 +10,14 @@ void kvm_arm_target_impl_cpu_init(void); #ifdef CONFIG_ARM_PKVM_GUEST void pkvm_init_hyp_services(void); +bool is_protected_kvm_guest(void); #else static inline void pkvm_init_hyp_services(void) { }; + +static inline bool is_protected_kvm_guest(void) +{ + return false; +} #endif static inline void kvm_arch_init_hyp_services(void) diff --git a/arch/arm64/include/asm/mem_encrypt.h b/arch/arm64/include/asm/mem_encrypt.h index 314b2b52025f..636f45b4d8af 100644 --- a/arch/arm64/include/asm/mem_encrypt.h +++ b/arch/arm64/include/asm/mem_encrypt.h @@ -2,6 +2,7 @@ #ifndef __ASM_MEM_ENCRYPT_H #define __ASM_MEM_ENCRYPT_H +#include <asm/hypervisor.h> #include <asm/rsi.h> struct device; @@ -20,7 +21,7 @@ int realm_register_memory_enc_ops(void); static inline bool force_dma_unencrypted(struct device *dev) { - return is_realm_world(); + return is_realm_world() || is_protected_kvm_guest(); } /* diff --git a/arch/arm64/kernel/rsi.c b/arch/arm64/kernel/rsi.c index 92160f2e57ff..25ca75ce1a4d 100644 --- a/arch/arm64/kernel/rsi.c +++ b/arch/arm64/kernel/rsi.c @@ -7,7 +7,6 @@ #include <linux/memblock.h> #include <linux/psci.h> #include <linux/swiotlb.h> -#include <linux/cc_platform.h> #include <linux/platform_device.h> #include <asm/io.h> @@ -23,17 +22,6 @@ EXPORT_SYMBOL(prot_ns_shared); DEFINE_STATIC_KEY_FALSE_RO(rsi_present); EXPORT_SYMBOL(rsi_present); -bool cc_platform_has(enum cc_attr attr) -{ - switch (attr) { - case CC_ATTR_MEM_ENCRYPT: - return is_realm_world(); - default: - return false; - } -} -EXPORT_SYMBOL_GPL(cc_platform_has); - static bool rsi_version_matches(void) { unsigned long ver_lower, ver_higher; diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c index acf67c7064db..a087ac5b15f7 100644 --- a/arch/arm64/mm/init.c +++ b/arch/arm64/mm/init.c @@ -12,6 +12,7 @@ #include <linux/swap.h> #include <linux/init.h> #include <linux/cache.h> +#include <linux/cc_platform.h> #include <linux/mman.h> #include <linux/nodemask.h> #include <linux/initrd.h> @@ -36,6 +37,7 @@ #include <asm/boot.h> #include <asm/fixmap.h> +#include <asm/hypervisor.h> #include <asm/kasan.h> #include <asm/kernel-pgtable.h> #include <asm/kvm_host.h> @@ -414,6 +416,17 @@ void dump_mem_limit(void) } } +bool cc_platform_has(enum cc_attr attr) +{ + switch (attr) { + case CC_ATTR_MEM_ENCRYPT: + return is_realm_world() || is_protected_kvm_guest(); + default: + return false; + } +} +EXPORT_SYMBOL_GPL(cc_platform_has); + #ifdef CONFIG_EXECMEM static u64 module_direct_base __ro_after_init = 0; static u64 module_plt_base __ro_after_init = 0; diff --git a/drivers/virt/coco/pkvm-guest/arm-pkvm-guest.c b/drivers/virt/coco/pkvm-guest/arm-pkvm-guest.c index 4230b817a80b..297e6d6019b8 100644 --- a/drivers/virt/coco/pkvm-guest/arm-pkvm-guest.c +++ b/drivers/virt/coco/pkvm-guest/arm-pkvm-guest.c @@ -95,6 +95,11 @@ static int mmio_guard_ioremap_hook(phys_addr_t phys, size_t size, return 0; } +bool is_protected_kvm_guest(void) +{ + return !!pkvm_granule; +} + void pkvm_init_hyp_services(void) { int i; -- 2.54.0.563.g4f69b47b94-goog Thanks, Mostafa > > -aneesh
