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Message-ID: <20260102155448.2554240-1-aneesh.kumar@kernel.org>
Date: Fri, 2 Jan 2026 21:24:48 +0530
From: "Aneesh Kumar K.V (Arm)" <aneesh.kumar@...nel.org>
To: iommu@...ts.linux.dev,
linux-kernel@...r.kernel.org,
linux-coco@...ts.linux.dev
Cc: Marek Szyprowski <m.szyprowski@...sung.com>,
Robin Murphy <robin.murphy@....com>,
steven.price@....com,
Suzuki K Poulose <suzuki.poulose@....com>,
"Aneesh Kumar K.V (Arm)" <aneesh.kumar@...nel.org>
Subject: [PATCH] dma-direct: swiotlb: Skip encryption toggles for swiotlb allocations
Swiotlb backing pages are already mapped decrypted via
swiotlb_update_mem_attributes(), so dma-direct does not need to call
set_memory_decrypted() during allocation or re-encrypt the memory on
free.
Handle swiotlb-backed buffers explicitly: obtain the DMA address and
zero the linear mapping for lowmem pages, and bypass the decrypt/encrypt
transitions when allocating/freeing from the swiotlb pool (detected via
swiotlb_find_pool()).
Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@...nel.org>
---
kernel/dma/direct.c | 56 +++++++++++++++++++++++++++++++++++++--------
1 file changed, 46 insertions(+), 10 deletions(-)
diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index faf1e41afde8..c4ef4457bd74 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -104,15 +104,27 @@ 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,
+ dma_addr_t *dma_handle)
{
- struct page *page = swiotlb_alloc(dev, size);
+ void *lm_addr;
+ struct page *page;
+
+ page = swiotlb_alloc(dev, size);
+ if (!page)
+ return NULL;
- if (page && !dma_coherent_ok(dev, page_to_phys(page), size)) {
+ if (!dma_coherent_ok(dev, page_to_phys(page), size)) {
swiotlb_free(dev, page, size);
return NULL;
}
+ /* If HighMem let caller take care of creating a mapping */
+ if (PageHighMem(page))
+ return page;
+ lm_addr = page_address(page);
+ memset(lm_addr, 0, size);
+ *dma_handle = phys_to_dma_direct(dev, page_to_phys(page));
return page;
}
@@ -125,9 +137,6 @@ 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 +213,7 @@ 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;
bool allow_highmem = true;
struct page *page;
void *ret;
@@ -251,6 +261,14 @@ 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, dma_handle);
+ if (page) {
+ mark_mem_decrypt = false;
+ goto setup_page;
+ }
+ return NULL;
+ }
if (force_dma_unencrypted(dev))
/*
@@ -266,6 +284,7 @@ void *dma_direct_alloc(struct device *dev, size_t size,
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
@@ -295,7 +314,7 @@ void *dma_direct_alloc(struct device *dev, size_t size,
ret = page_address(page);
}
- if (force_dma_unencrypted(dev)) {
+ if (mark_mem_decrypt && force_dma_unencrypted(dev)) {
void *lm_addr;
lm_addr = page_address(page);
@@ -316,7 +335,7 @@ 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);
@@ -328,6 +347,7 @@ 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) &&
@@ -356,6 +376,9 @@ 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 {
@@ -363,7 +386,7 @@ void dma_direct_free(struct device *dev, size_t size,
arch_dma_clear_uncached(cpu_addr, size);
}
- if (force_dma_unencrypted(dev)) {
+ if (mark_mem_encrypted && force_dma_unencrypted(dev)) {
void *lm_addr;
lm_addr = phys_to_virt(dma_to_phys(dev, dma_addr));
@@ -385,6 +408,15 @@ 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, dma_handle);
+ if (page && PageHighMem(page)) {
+ swiotlb_free(dev, page, size);
+ return NULL;
+ }
+ return page;
+ }
+
page = __dma_direct_alloc_pages(dev, size, gfp, false);
if (!page)
return NULL;
@@ -404,13 +436,17 @@ 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
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