[PATCH v3 6/9] dma-direct: pass attrs to dma_capable() for DMA_ATTR_CC_SHARED checks

Aneesh Kumar K.V (Arm)
2026-04-27T05:55:57Z

Teach dma_capable() about DMA_ATTR_CC_SHARED so the capability
check can reject encrypted DMA addresses for devices that require
unencrypted/shared DMA.

Also propagate DMA_ATTR_CC_SHARED in swiotlb_map() when the selected
SWIOTLB pool is decrypted so the capability check sees the correct DMA
address attribute.

Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
arch/x86/kernel/amd_gart_64.c | 30 ++++++++++++++++--------------
drivers/xen/swiotlb-xen.c | 9 ++++++---
include/linux/dma-direct.h | 9 ++++++++-
kernel/dma/direct.h | 6 +++---
kernel/dma/swiotlb.c | 8 +++++---
5 files changed, 38 insertions(+), 24 deletions(-)

diff --git a/arch/x86/kernel/amd_gart_64.c b/arch/x86/kernel/amd_gart_64.c
index e8000a56732e..b5f1f031d45b 100644
--- a/arch/x86/kernel/amd_gart_64.c
+++ b/arch/x86/kernel/amd_gart_64.c
@@ -180,22 +180,23 @@ static void iommu_full(struct device *dev, size_t size, int dir)
}

static inline int
-need_iommu(struct device *dev, unsigned long addr, size_t size)
+need_iommu(struct device *dev, unsigned long addr, size_t size, unsigned long attrs)
{
- return force_iommu || !dma_capable(dev, addr, size, true);
+ return force_iommu || !dma_capable(dev, addr, size, true, attrs);
}

static inline int
-nonforced_iommu(struct device *dev, unsigned long addr, size_t size)
+nonforced_iommu(struct device *dev, unsigned long addr, size_t size,
+ unsigned long attrs)
{
- return !dma_capable(dev, addr, size, true);
+ return !dma_capable(dev, addr, size, true, attrs);
}

/* Map a single continuous physical area into the IOMMU.
* Caller needs to check if the iommu is needed and flush.
*/
static dma_addr_t dma_map_area(struct device *dev, dma_addr_t phys_mem,
- size_t size, int dir, unsigned long align_mask)
+ size_t size, int dir, unsigned long align_mask, unsigned long attrs)
{
unsigned long npages = iommu_num_pages(phys_mem, size, PAGE_SIZE);
unsigned long iommu_page;
@@ -206,7 +207,7 @@ static dma_addr_t dma_map_area(struct device *dev, dma_addr_t phys_mem,

iommu_page = alloc_iommu(dev, npages, align_mask);
if (iommu_page == -1) {
- if (!nonforced_iommu(dev, phys_mem, size))
+ if (!nonforced_iommu(dev, phys_mem, size, attrs))
return phys_mem;
if (panic_on_overflow)
panic("dma_map_area overflow %lu bytes\n", size);
@@ -231,10 +232,10 @@ static dma_addr_t gart_map_phys(struct device *dev, phys_addr_t paddr,
if (unlikely(attrs & DMA_ATTR_MMIO))
return DMA_MAPPING_ERROR;

- if (!need_iommu(dev, paddr, size))
+ if (!need_iommu(dev, paddr, size, attrs))
return paddr;

- bus = dma_map_area(dev, paddr, size, dir, 0);
+ bus = dma_map_area(dev, paddr, size, dir, 0, attrs);
flush_gart();

return bus;
@@ -289,7 +290,7 @@ static void gart_unmap_sg(struct device *dev, struct scatterlist *sg, int nents,

/* Fallback for dma_map_sg in case of overflow */
static int dma_map_sg_nonforce(struct device *dev, struct scatterlist *sg,
- int nents, int dir)
+ int nents, int dir, unsigned long attrs)
{
struct scatterlist *s;
int i;
@@ -301,8 +302,8 @@ static int dma_map_sg_nonforce(struct device *dev, struct scatterlist *sg,
for_each_sg(sg, s, nents, i) {
unsigned long addr = sg_phys(s);

- if (nonforced_iommu(dev, addr, s->length)) {
- addr = dma_map_area(dev, addr, s->length, dir, 0);
+ if (nonforced_iommu(dev, addr, s->length, attrs)) {
+ addr = dma_map_area(dev, addr, s->length, dir, 0, attrs);
if (addr == DMA_MAPPING_ERROR) {
if (i > 0)
gart_unmap_sg(dev, sg, i, dir, 0);
@@ -401,7 +402,7 @@ static int gart_map_sg(struct device *dev, struct scatterlist *sg, int nents,
s->dma_address = addr;
BUG_ON(s->length == 0);

- nextneed = need_iommu(dev, addr, s->length);
+ nextneed = need_iommu(dev, addr, s->length, attrs);

/* Handle the previous not yet processed entries */
if (i > start) {
@@ -449,7 +450,7 @@ static int gart_map_sg(struct device *dev, struct scatterlist *sg, int nents,

/* When it was forced or merged try again in a dumb way */
if (force_iommu || iommu_merge) {
- out = dma_map_sg_nonforce(dev, sg, nents, dir);
+ out = dma_map_sg_nonforce(dev, sg, nents, dir, attrs);
if (out > 0)
return out;
}
@@ -473,7 +474,8 @@ gart_alloc_coherent(struct device *dev, size_t size, dma_addr_t *dma_addr,
return vaddr;

*dma_addr = dma_map_area(dev, virt_to_phys(vaddr), size,
- DMA_BIDIRECTIONAL, (1UL << get_order(size)) - 1);
+ DMA_BIDIRECTIONAL,
+ (1UL << get_order(size)) - 1, attrs);
flush_gart();
if (unlikely(*dma_addr == DMA_MAPPING_ERROR))
goto out_free;
diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index 2cbf2b588f5b..7584c6f42141 100644
--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -212,7 +212,7 @@ static dma_addr_t xen_swiotlb_map_phys(struct device *dev, phys_addr_t phys,
BUG_ON(dir == DMA_NONE);

if (attrs & DMA_ATTR_MMIO) {
- if (unlikely(!dma_capable(dev, phys, size, false))) {
+ if (unlikely(!dma_capable(dev, phys, size, false, attrs))) {
dev_err_once(
dev,
"DMA addr %pa+%zu overflow (mask %llx, bus limit %llx).\n",
@@ -231,7 +231,7 @@ static dma_addr_t xen_swiotlb_map_phys(struct device *dev, phys_addr_t phys,
* we can safely return the device addr and not worry about bounce
* buffering it.
*/
- if (dma_capable(dev, dev_addr, size, true) &&
+ if (dma_capable(dev, dev_addr, size, true, attrs) &&
!dma_kmalloc_needs_bounce(dev, size, dir) &&
!range_straddles_page_boundary(phys, size) &&
!xen_arch_need_swiotlb(dev, phys, dev_addr) &&
@@ -250,10 +250,13 @@ static dma_addr_t xen_swiotlb_map_phys(struct device *dev, phys_addr_t phys,
phys = map;
dev_addr = xen_phys_to_dma(dev, map);

+ if (dev->dma_io_tlb_mem->decrypted)
+ attrs |= DMA_ATTR_CC_SHARED;
+
/*
* Ensure that the address returned is DMA'ble
*/
- if (unlikely(!dma_capable(dev, dev_addr, size, true))) {
+ if (unlikely(!dma_capable(dev, dev_addr, size, true, attrs))) {
__swiotlb_tbl_unmap_single(dev, map, size, dir,
attrs | DMA_ATTR_SKIP_CPU_SYNC,
swiotlb_find_pool(dev, map));
diff --git a/include/linux/dma-direct.h b/include/linux/dma-direct.h
index 94fad4e7c11e..1281d91050a4 100644
--- a/include/linux/dma-direct.h
+++ b/include/linux/dma-direct.h
@@ -135,12 +135,19 @@ static inline bool force_dma_unencrypted(struct device *dev)
#endif /* CONFIG_ARCH_HAS_FORCE_DMA_UNENCRYPTED */

static inline bool dma_capable(struct device *dev, dma_addr_t addr, size_t size,
- bool is_ram)
+ bool is_ram, unsigned long attrs)
{
dma_addr_t end = addr + size - 1;

if (addr == DMA_MAPPING_ERROR)
return false;
+ /*
+ * if phys addr attribute is encrypted but the
+ * device is forcing an encrypted dma addr
+ */
+ if (!(attrs & DMA_ATTR_CC_SHARED) && force_dma_unencrypted(dev))
+ return false;
+
if (is_ram && !IS_ENABLED(CONFIG_ARCH_DMA_ADDR_T_64BIT) &&
min(addr, end) < phys_to_dma(dev, PFN_PHYS(min_low_pfn)))
return false;
diff --git a/kernel/dma/direct.h b/kernel/dma/direct.h
index 7140c208c123..e05dc7649366 100644
--- a/kernel/dma/direct.h
+++ b/kernel/dma/direct.h
@@ -101,15 +101,15 @@ static inline dma_addr_t dma_direct_map_phys(struct device *dev,

if (attrs & DMA_ATTR_MMIO) {
dma_addr = phys;
- if (unlikely(!dma_capable(dev, dma_addr, size, false)))
+ if (unlikely(!dma_capable(dev, dma_addr, size, false, attrs)))
goto err_overflow;
} else if (attrs & DMA_ATTR_CC_SHARED) {
dma_addr = phys_to_dma_unencrypted(dev, phys);
- if (unlikely(!dma_capable(dev, dma_addr, size, false)))
+ if (unlikely(!dma_capable(dev, dma_addr, size, false, attrs)))
goto err_overflow;
} else {
dma_addr = phys_to_dma(dev, phys);
- if (unlikely(!dma_capable(dev, dma_addr, size, true)) ||
+ if (unlikely(!dma_capable(dev, dma_addr, size, true, attrs)) ||
dma_kmalloc_needs_bounce(dev, size, dir)) {
if (is_swiotlb_active(dev) &&
!(attrs & DMA_ATTR_REQUIRE_COHERENT))
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index dad351988daf..0d3ae9a0130a 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -1640,12 +1640,14 @@ dma_addr_t swiotlb_map(struct device *dev, phys_addr_t paddr, size_t size,
/*
* Use the allocated io_tlb_mem encryption type to determine dma addr.
*/
- if (dev->dma_io_tlb_mem->decrypted)
+ if (dev->dma_io_tlb_mem->decrypted) {
dma_addr = phys_to_dma_unencrypted(dev, swiotlb_addr);
- else
+ attrs |= DMA_ATTR_CC_SHARED;
+ } else {
dma_addr = phys_to_dma_encrypted(dev, swiotlb_addr);
+ }

- if (unlikely(!dma_capable(dev, dma_addr, size, true))) {
+ if (unlikely(!dma_capable(dev, dma_addr, size, true, attrs))) {
__swiotlb_tbl_unmap_single(dev, swiotlb_addr, size, dir,
attrs | DMA_ATTR_SKIP_CPU_SYNC,
swiotlb_find_pool(dev, swiotlb_addr));
--
2.43.0