[PATCH v4 1/3] dma-direct: swiotlb: handle swiotlb alloc/free outside __dma_direct_alloc_pages

Aneesh Kumar K.V (Arm)
2026-04-27T06:31:30Z

Move swiotlb allocation out of __dma_direct_alloc_pages() and handle it in
dma_direct_alloc() / dma_direct_alloc_pages().

This is needed for follow-up changes that align shared decrypted buffers to
hypervisor page size. swiotlb pool memory is decrypted as a whole and does
not need per-allocation alignment handling.

swiotlb backing pages are already mapped decrypted by
swiotlb_update_mem_attributes() and rmem_swiotlb_device_init(), so
dma-direct should not call dma_set_decrypted() on allocation nor
dma_set_encrypted() on free for swiotlb-backed memory.

Update alloc/free paths to detect swiotlb-backed pages and skip
encrypt/decrypt transitions for those paths. Keep the existing highmem
rejection in dma_direct_alloc_pages() for swiotlb allocations.

Only for "restricted-dma-pool", we currently set `for_alloc = true`, while
rmem_swiotlb_device_init() decrypts the whole pool up front. This pool is
typically used together with "shared-dma-pool", where the shared region is
accessed after remap/ioremap and the returned address is suitable for
decrypted memory access. So existing code paths remain valid.

Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
kernel/dma/direct.c | 44 +++++++++++++++++++++++++++++++++++++-------
1 file changed, 37 insertions(+), 7 deletions(-)

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 8f43a930716d..c2a43e4ef902 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -125,9 +125,6 @@ static struct page *__dma_direct_alloc_pages(struct device *dev, size_t size,

WARN_ON_ONCE(!PAGE_ALIGNED(size));

- if (is_swiotlb_for_alloc(dev))
- return dma_direct_alloc_swiotlb(dev, size);
-
gfp |= dma_direct_optimal_gfp_mask(dev, &phys_limit);
page = dma_alloc_contiguous(dev, size, gfp);
if (page) {
@@ -204,6 +201,7 @@ void *dma_direct_alloc(struct device *dev, size_t size,
dma_addr_t *dma_handle, gfp_t gfp, unsigned long attrs)
{
bool remap = false, set_uncached = false;
+ bool mark_mem_decrypt = true;
struct page *page;
void *ret;

@@ -250,11 +248,21 @@ void *dma_direct_alloc(struct device *dev, size_t size,
dma_direct_use_pool(dev, gfp))
return dma_direct_alloc_from_pool(dev, size, dma_handle, gfp);

+ if (is_swiotlb_for_alloc(dev)) {
+ page = dma_direct_alloc_swiotlb(dev, size);
+ if (page) {
+ mark_mem_decrypt = false;
+ goto setup_page;
+ }
+ return NULL;
+ }
+
/* we always manually zero the memory once we are done */
page = __dma_direct_alloc_pages(dev, size, gfp & ~__GFP_ZERO, true);
if (!page)
return NULL;

+setup_page:
/*
* dma_alloc_contiguous can return highmem pages depending on a
* combination the cma= arguments and per-arch setup. These need to be
@@ -281,7 +289,7 @@ void *dma_direct_alloc(struct device *dev, size_t size,
goto out_free_pages;
} else {
ret = page_address(page);
- if (dma_set_decrypted(dev, ret, size))
+ if (mark_mem_decrypt && dma_set_decrypted(dev, ret, size))
goto out_leak_pages;
}

@@ -298,7 +306,7 @@ void *dma_direct_alloc(struct device *dev, size_t size,
return ret;

out_encrypt_pages:
- if (dma_set_encrypted(dev, page_address(page), size))
+ if (mark_mem_decrypt && dma_set_encrypted(dev, page_address(page), size))
return NULL;
out_free_pages:
__dma_direct_free_pages(dev, page, size);
@@ -310,6 +318,7 @@ void *dma_direct_alloc(struct device *dev, size_t size,
void dma_direct_free(struct device *dev, size_t size,
void *cpu_addr, dma_addr_t dma_addr, unsigned long attrs)
{
+ bool mark_mem_encrypted = true;
unsigned int page_order = get_order(size);

if ((attrs & DMA_ATTR_NO_KERNEL_MAPPING) &&
@@ -338,12 +347,15 @@ void dma_direct_free(struct device *dev, size_t size,
dma_free_from_pool(dev, cpu_addr, PAGE_ALIGN(size)))
return;

+ if (swiotlb_find_pool(dev, dma_to_phys(dev, dma_addr)))
+ mark_mem_encrypted = false;
+
if (is_vmalloc_addr(cpu_addr)) {
vunmap(cpu_addr);
} else {
if (IS_ENABLED(CONFIG_ARCH_HAS_DMA_CLEAR_UNCACHED))
arch_dma_clear_uncached(cpu_addr, size);
- if (dma_set_encrypted(dev, cpu_addr, size))
+ if (mark_mem_encrypted && dma_set_encrypted(dev, cpu_addr, size))
return;
}

@@ -359,6 +371,19 @@ struct page *dma_direct_alloc_pages(struct device *dev, size_t size,
if (force_dma_unencrypted(dev) && dma_direct_use_pool(dev, gfp))
return dma_direct_alloc_from_pool(dev, size, dma_handle, gfp);

+ if (is_swiotlb_for_alloc(dev)) {
+ page = dma_direct_alloc_swiotlb(dev, size);
+ if (!page)
+ return NULL;
+
+ if (PageHighMem(page)) {
+ swiotlb_free(dev, page, size);
+ return NULL;
+ }
+ ret = page_address(page);
+ goto setup_page;
+ }
+
page = __dma_direct_alloc_pages(dev, size, gfp, false);
if (!page)
return NULL;
@@ -366,6 +391,7 @@ struct page *dma_direct_alloc_pages(struct device *dev, size_t size,
ret = page_address(page);
if (dma_set_decrypted(dev, ret, size))
goto out_leak_pages;
+setup_page:
memset(ret, 0, size);
*dma_handle = phys_to_dma_direct(dev, page_to_phys(page));
return page;
@@ -378,13 +404,17 @@ void dma_direct_free_pages(struct device *dev, size_t size,
enum dma_data_direction dir)
{
void *vaddr = page_address(page);
+ bool mark_mem_encrypted = true;

/* If cpu_addr is not from an atomic pool, dma_free_from_pool() fails */
if (IS_ENABLED(CONFIG_DMA_COHERENT_POOL) &&
dma_free_from_pool(dev, vaddr, size))
return;

- if (dma_set_encrypted(dev, vaddr, size))
+ if (swiotlb_find_pool(dev, page_to_phys(page)))
+ mark_mem_encrypted = false;
+
+ if (mark_mem_encrypted && dma_set_encrypted(dev, vaddr, size))
return;
__dma_direct_free_pages(dev, page, size);
}
--
2.43.0