[PATCH v3 3/9] dma-pool: track decrypted atomic pools and select them via attrs

Aneesh Kumar K.V (Arm)
2026-04-27T05:55:40Z

Teach the atomic DMA pool code to distinguish between encrypted and
decrypted pools, and make pool allocation select the matching pool based
on DMA attributes.

Introduce a dma_gen_pool wrapper that records whether a pool is
decrypted, initialize that state when the atomic pools are created, and
use it when expanding and resizing the pools. Update dma_alloc_from_pool()
to take attrs and skip pools whose encrypted/decrypted state does not
match DMA_ATTR_CC_SHARED. Update dma_free_from_pool() accordingly.

Also pass DMA_ATTR_CC_SHARED from the swiotlb atomic allocation path
so decrypted swiotlb allocations are taken from the correct atomic pool.

Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
drivers/iommu/dma-iommu.c | 2 +-
include/linux/dma-map-ops.h | 2 +-
kernel/dma/direct.c | 11 ++-
kernel/dma/pool.c | 154 +++++++++++++++++++++++-------------
kernel/dma/swiotlb.c | 2 +
5 files changed, 109 insertions(+), 62 deletions(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index 54d96e847f16..c2595bee3d41 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -1673,7 +1673,7 @@ void *iommu_dma_alloc(struct device *dev, size_t size, dma_addr_t *handle,
if (IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) &&
!gfpflags_allow_blocking(gfp) && !coherent)
page = dma_alloc_from_pool(dev, PAGE_ALIGN(size), &cpu_addr,
- gfp, NULL);
+ gfp, attrs, NULL);
else
cpu_addr = iommu_dma_alloc_pages(dev, size, &page, gfp, attrs);
if (!cpu_addr)
diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h
index 6a1832a73cad..696b2c3a2305 100644
--- a/include/linux/dma-map-ops.h
+++ b/include/linux/dma-map-ops.h
@@ -212,7 +212,7 @@ void *dma_common_pages_remap(struct page **pages, size_t size, pgprot_t prot,
void dma_common_free_remap(void *cpu_addr, size_t size);

struct page *dma_alloc_from_pool(struct device *dev, size_t size,
- void **cpu_addr, gfp_t flags,
+ void **cpu_addr, gfp_t flags, unsigned long attrs,
bool (*phys_addr_ok)(struct device *, phys_addr_t, size_t));
bool dma_free_from_pool(struct device *dev, void *start, size_t size);

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 0c2e1f8436ce..707d410b3669 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -162,7 +162,7 @@ static bool dma_direct_use_pool(struct device *dev, gfp_t gfp)
}

static void *dma_direct_alloc_from_pool(struct device *dev, size_t size,
- dma_addr_t *dma_handle, gfp_t gfp)
+ dma_addr_t *dma_handle, gfp_t gfp, unsigned long attrs)
{
struct page *page;
u64 phys_limit;
@@ -172,7 +172,8 @@ static void *dma_direct_alloc_from_pool(struct device *dev, size_t size,
return NULL;

gfp |= dma_direct_optimal_gfp_mask(dev, &phys_limit);
- page = dma_alloc_from_pool(dev, size, &ret, gfp, dma_coherent_ok);
+ page = dma_alloc_from_pool(dev, size, &ret, gfp, attrs,
+ dma_coherent_ok);
if (!page)
return NULL;
*dma_handle = phys_to_dma_direct(dev, page_to_phys(page));
@@ -261,7 +262,8 @@ void *dma_direct_alloc(struct device *dev, size_t size,
*/
if ((remap || (attrs & DMA_ATTR_CC_SHARED)) &&
dma_direct_use_pool(dev, gfp))
- return dma_direct_alloc_from_pool(dev, size, dma_handle, gfp);
+ return dma_direct_alloc_from_pool(dev, size, dma_handle,
+ gfp, attrs);

if (is_swiotlb_for_alloc(dev)) {
page = dma_direct_alloc_swiotlb(dev, size);
@@ -397,7 +399,8 @@ struct page *dma_direct_alloc_pages(struct device *dev, size_t size,
attrs |= DMA_ATTR_CC_SHARED;

if ((attrs & DMA_ATTR_CC_SHARED) && dma_direct_use_pool(dev, gfp))
- return dma_direct_alloc_from_pool(dev, size, dma_handle, gfp);
+ return dma_direct_alloc_from_pool(dev, size, dma_handle,
+ gfp, attrs);

if (is_swiotlb_for_alloc(dev)) {
page = dma_direct_alloc_swiotlb(dev, size);
diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
index 2b2fbb709242..e41e19701e50 100644
--- a/kernel/dma/pool.c
+++ b/kernel/dma/pool.c
@@ -12,12 +12,18 @@
#include <linux/set_memory.h>
#include <linux/slab.h>
#include <linux/workqueue.h>
+#include <linux/cc_platform.h>

-static struct gen_pool *atomic_pool_dma __ro_after_init;
+struct dma_gen_pool {
+ bool decrypted;
+ struct gen_pool *pool;
+};
+
+static struct dma_gen_pool atomic_pool_dma __ro_after_init;
static unsigned long pool_size_dma;
-static struct gen_pool *atomic_pool_dma32 __ro_after_init;
+static struct dma_gen_pool atomic_pool_dma32 __ro_after_init;
static unsigned long pool_size_dma32;
-static struct gen_pool *atomic_pool_kernel __ro_after_init;
+static struct dma_gen_pool atomic_pool_kernel __ro_after_init;
static unsigned long pool_size_kernel;

/* Size can be defined by the coherent_pool command line */
@@ -76,7 +82,7 @@ static bool cma_in_zone(gfp_t gfp)
return true;
}

-static int atomic_pool_expand(struct gen_pool *pool, size_t pool_size,
+static int atomic_pool_expand(struct dma_gen_pool *dma_pool, size_t pool_size,
gfp_t gfp)
{
unsigned int order;
@@ -113,11 +119,14 @@ static int atomic_pool_expand(struct gen_pool *pool, size_t pool_size,
* Memory in the atomic DMA pools must be unencrypted, the pools do not
* shrink so no re-encryption occurs in dma_direct_free().
*/
- ret = set_memory_decrypted((unsigned long)page_to_virt(page),
+ if (dma_pool->decrypted) {
+ ret = set_memory_decrypted((unsigned long)page_to_virt(page),
1 << order);
- if (ret)
- goto remove_mapping;
- ret = gen_pool_add_virt(pool, (unsigned long)addr, page_to_phys(page),
+ if (ret)
+ goto remove_mapping;
+ }
+
+ ret = gen_pool_add_virt(dma_pool->pool, (unsigned long)addr, page_to_phys(page),
pool_size, NUMA_NO_NODE);
if (ret)
goto encrypt_mapping;
@@ -126,11 +135,13 @@ static int atomic_pool_expand(struct gen_pool *pool, size_t pool_size,
return 0;

encrypt_mapping:
- ret = set_memory_encrypted((unsigned long)page_to_virt(page),
- 1 << order);
- if (WARN_ON_ONCE(ret)) {
- /* Decrypt succeeded but encrypt failed, purposely leak */
- goto out;
+ if (dma_pool->decrypted) {
+ ret = set_memory_encrypted((unsigned long)page_to_virt(page),
+ 1 << order);
+ if (WARN_ON_ONCE(ret)) {
+ /* Decrypt succeeded but encrypt failed, purposely leak */
+ goto out;
+ }
}
remove_mapping:
#ifdef CONFIG_DMA_DIRECT_REMAP
@@ -142,46 +153,51 @@ static int atomic_pool_expand(struct gen_pool *pool, size_t pool_size,
return ret;
}

-static void atomic_pool_resize(struct gen_pool *pool, gfp_t gfp)
+static void atomic_pool_resize(struct dma_gen_pool *dma_pool, gfp_t gfp)
{
- if (pool && gen_pool_avail(pool) < atomic_pool_size)
- atomic_pool_expand(pool, gen_pool_size(pool), gfp);
+ if (dma_pool->pool && gen_pool_avail(dma_pool->pool) < atomic_pool_size)
+ atomic_pool_expand(dma_pool, gen_pool_size(dma_pool->pool), gfp);
}

static void atomic_pool_work_fn(struct work_struct *work)
{
if (IS_ENABLED(CONFIG_ZONE_DMA))
- atomic_pool_resize(atomic_pool_dma,
+ atomic_pool_resize(&atomic_pool_dma,
GFP_KERNEL | GFP_DMA);
if (IS_ENABLED(CONFIG_ZONE_DMA32))
- atomic_pool_resize(atomic_pool_dma32,
+ atomic_pool_resize(&atomic_pool_dma32,
GFP_KERNEL | GFP_DMA32);
- atomic_pool_resize(atomic_pool_kernel, GFP_KERNEL);
+ atomic_pool_resize(&atomic_pool_kernel, GFP_KERNEL);
}

-static __init struct gen_pool *__dma_atomic_pool_init(size_t pool_size,
- gfp_t gfp)
+static __init struct dma_gen_pool *__dma_atomic_pool_init(struct dma_gen_pool *dma_pool,
+ size_t pool_size, gfp_t gfp)
{
- struct gen_pool *pool;
int ret;

- pool = gen_pool_create(PAGE_SHIFT, NUMA_NO_NODE);
- if (!pool)
+ dma_pool->pool = gen_pool_create(PAGE_SHIFT, NUMA_NO_NODE);
+ if (!dma_pool->pool)
return NULL;

- gen_pool_set_algo(pool, gen_pool_first_fit_order_align, NULL);
+ gen_pool_set_algo(dma_pool->pool, gen_pool_first_fit_order_align, NULL);
+
+ /* if platform is using memory encryption atomic pools are by default decrypted. */
+ if (cc_platform_has(CC_ATTR_MEM_ENCRYPT))
+ dma_pool->decrypted = true;
+ else
+ dma_pool->decrypted = false;

- ret = atomic_pool_expand(pool, pool_size, gfp);
+ ret = atomic_pool_expand(dma_pool, pool_size, gfp);
if (ret) {
- gen_pool_destroy(pool);
+ gen_pool_destroy(dma_pool->pool);
pr_err("DMA: failed to allocate %zu KiB %pGg pool for atomic allocation\n",
pool_size >> 10, &gfp);
return NULL;
}

pr_info("DMA: preallocated %zu KiB %pGg pool for atomic allocations\n",
- gen_pool_size(pool) >> 10, &gfp);
- return pool;
+ gen_pool_size(dma_pool->pool) >> 10, &gfp);
+ return dma_pool;
}

#ifdef CONFIG_ZONE_DMA32
@@ -207,21 +223,22 @@ static int __init dma_atomic_pool_init(void)

/* All memory might be in the DMA zone(s) to begin with */
if (has_managed_zone(ZONE_NORMAL)) {
- atomic_pool_kernel = __dma_atomic_pool_init(atomic_pool_size,
- GFP_KERNEL);
- if (!atomic_pool_kernel)
+ __dma_atomic_pool_init(&atomic_pool_kernel, atomic_pool_size, GFP_KERNEL);
+ if (!atomic_pool_kernel.pool)
ret = -ENOMEM;
}
+
if (has_managed_dma()) {
- atomic_pool_dma = __dma_atomic_pool_init(atomic_pool_size,
- GFP_KERNEL | GFP_DMA);
- if (!atomic_pool_dma)
+ __dma_atomic_pool_init(&atomic_pool_dma, atomic_pool_size,
+ GFP_KERNEL | GFP_DMA);
+ if (!atomic_pool_dma.pool)
ret = -ENOMEM;
}
+
if (has_managed_dma32) {
- atomic_pool_dma32 = __dma_atomic_pool_init(atomic_pool_size,
- GFP_KERNEL | GFP_DMA32);
- if (!atomic_pool_dma32)
+ __dma_atomic_pool_init(&atomic_pool_dma32, atomic_pool_size,
+ GFP_KERNEL | GFP_DMA32);
+ if (!atomic_pool_dma32.pool)
ret = -ENOMEM;
}

@@ -230,19 +247,38 @@ static int __init dma_atomic_pool_init(void)
}
postcore_initcall(dma_atomic_pool_init);

-static inline struct gen_pool *dma_guess_pool(struct gen_pool *prev, gfp_t gfp)
+static inline struct dma_gen_pool *dma_guess_pool(struct dma_gen_pool *prev, gfp_t gfp)
{
if (prev == NULL) {
- if (gfp & GFP_DMA)
- return atomic_pool_dma ?: atomic_pool_dma32 ?: atomic_pool_kernel;
- if (gfp & GFP_DMA32)
- return atomic_pool_dma32 ?: atomic_pool_dma ?: atomic_pool_kernel;
- return atomic_pool_kernel ?: atomic_pool_dma32 ?: atomic_pool_dma;
+ if (gfp & GFP_DMA) {
+ if (atomic_pool_dma.pool)
+ return &atomic_pool_dma;
+ if (atomic_pool_dma32.pool)
+ return &atomic_pool_dma32;
+ return &atomic_pool_kernel;
+ }
+
+ if (gfp & GFP_DMA32) {
+ if (atomic_pool_dma32.pool)
+ return &atomic_pool_dma32;
+ if (atomic_pool_dma.pool)
+ return &atomic_pool_dma;
+ return &atomic_pool_kernel;
+ }
+ if (atomic_pool_kernel.pool)
+ return &atomic_pool_kernel;
+ if (atomic_pool_dma32.pool)
+ return &atomic_pool_dma32;
+ if (atomic_pool_dma.pool)
+ return &atomic_pool_dma;
}
- if (prev == atomic_pool_kernel)
- return atomic_pool_dma32 ? atomic_pool_dma32 : atomic_pool_dma;
- if (prev == atomic_pool_dma32)
- return atomic_pool_dma;
+ if (prev == &atomic_pool_kernel) {
+ if (atomic_pool_dma32.pool)
+ return &atomic_pool_dma32;
+ return &atomic_pool_dma;
+ }
+ if (prev == &atomic_pool_dma32)
+ return &atomic_pool_dma;
return NULL;
}

@@ -272,16 +308,20 @@ static struct page *__dma_alloc_from_pool(struct device *dev, size_t size,
}

struct page *dma_alloc_from_pool(struct device *dev, size_t size,
- void **cpu_addr, gfp_t gfp,
+ void **cpu_addr, gfp_t gfp, unsigned long attrs,
bool (*phys_addr_ok)(struct device *, phys_addr_t, size_t))
{
- struct gen_pool *pool = NULL;
+ struct dma_gen_pool *dma_pool = NULL;
struct page *page;
bool pool_found = false;

- while ((pool = dma_guess_pool(pool, gfp))) {
+ while ((dma_pool = dma_guess_pool(dma_pool, gfp))) {
+
+ if (dma_pool->decrypted != !!(attrs & DMA_ATTR_CC_SHARED))
+ continue;
+
pool_found = true;
- page = __dma_alloc_from_pool(dev, size, pool, cpu_addr,
+ page = __dma_alloc_from_pool(dev, size, dma_pool->pool, cpu_addr,
phys_addr_ok);
if (page)
return page;
@@ -296,12 +336,14 @@ struct page *dma_alloc_from_pool(struct device *dev, size_t size,

bool dma_free_from_pool(struct device *dev, void *start, size_t size)
{
- struct gen_pool *pool = NULL;
+ struct dma_gen_pool *dma_pool = NULL;

- while ((pool = dma_guess_pool(pool, 0))) {
- if (!gen_pool_has_addr(pool, (unsigned long)start, size))
+ while ((dma_pool = dma_guess_pool(dma_pool, 0))) {
+
+ if (!gen_pool_has_addr(dma_pool->pool, (unsigned long)start, size))
continue;
- gen_pool_free(pool, (unsigned long)start, size);
+
+ gen_pool_free(dma_pool->pool, (unsigned long)start, size);
return true;
}

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 1abd3e6146f4..b215b274a873 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -623,7 +623,9 @@ static struct page *swiotlb_alloc_tlb(struct device *dev, size_t bytes,
if (!IS_ENABLED(CONFIG_DMA_COHERENT_POOL))
return NULL;

+ /* considered decrypted by default */
return dma_alloc_from_pool(dev, bytes, &vaddr, gfp,
+ DMA_ATTR_CC_SHARED,
dma_coherent_ok);
}

--
2.43.0