[RFC PATCH v1 04/38] tsm: Support DMA Allocation from private memory

Aneesh Kumar K.V (Arm)
2025-07-28T13:53:00Z

Currently, we enforce the use of bounce buffers to ensure that memory
accessed by non-secure devices is explicitly shared with the host [1].
However, for secure devices, this approach must be avoided.

To achieve this, we introduce a device flag that controls whether a
bounce buffer allocation is required for the device. Additionally, this flag is
used to manage the top IPA bit assignment for setting up
protected/unprotected IPA aliases.

[1] commit fbf979a01375 ("arm64: Enforce bounce buffers for realm DMA")

based on changes from Alexey Kardashevskiy <aik@amd.com>
Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
arch/arm64/include/asm/mem_encrypt.h | 6 +-----
arch/arm64/mm/mem_encrypt.c | 10 ++++++++++
drivers/pci/tsm.c | 6 ++++++
include/linux/device.h | 1 +
include/linux/swiotlb.h | 4 ++++
5 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/include/asm/mem_encrypt.h b/arch/arm64/include/asm/mem_encrypt.h
index 314b2b52025f..d77c10cd5b79 100644
--- a/arch/arm64/include/asm/mem_encrypt.h
+++ b/arch/arm64/include/asm/mem_encrypt.h
@@ -15,14 +15,10 @@ int arm64_mem_crypt_ops_register(const struct arm64_mem_crypt_ops *ops);

int set_memory_encrypted(unsigned long addr, int numpages);
int set_memory_decrypted(unsigned long addr, int numpages);
+bool force_dma_unencrypted(struct device *dev);

int realm_register_memory_enc_ops(void);

-static inline bool force_dma_unencrypted(struct device *dev)
-{
- return is_realm_world();
-}
-
/*
* For Arm CCA guests, canonical addresses are "encrypted", so no changes
* required for dma_addr_encrypted().
diff --git a/arch/arm64/mm/mem_encrypt.c b/arch/arm64/mm/mem_encrypt.c
index ee3c0ab04384..279696a8af3f 100644
--- a/arch/arm64/mm/mem_encrypt.c
+++ b/arch/arm64/mm/mem_encrypt.c
@@ -17,6 +17,7 @@
#include <linux/compiler.h>
#include <linux/err.h>
#include <linux/mm.h>
+#include <linux/device.h>

#include <asm/mem_encrypt.h>

@@ -48,3 +49,12 @@ int set_memory_decrypted(unsigned long addr, int numpages)
return crypt_ops->decrypt(addr, numpages);
}
EXPORT_SYMBOL_GPL(set_memory_decrypted);
+
+bool force_dma_unencrypted(struct device *dev)
+{
+ if (dev->tdi_enabled)
+ return false;
+
+ return is_realm_world();
+}
+EXPORT_SYMBOL_GPL(force_dma_unencrypted);
diff --git a/drivers/pci/tsm.c b/drivers/pci/tsm.c
index e4a3b5b37939..60f50d57a725 100644
--- a/drivers/pci/tsm.c
+++ b/drivers/pci/tsm.c
@@ -120,6 +120,7 @@ static int pci_tsm_disconnect(struct pci_dev *pdev)

tsm_ops->disconnect(pdev);
tsm->state = PCI_TSM_INIT;
+ pdev->dev.tdi_enabled = false;

return 0;
}
@@ -199,6 +200,8 @@ static int pci_tsm_accept(struct pci_dev *pdev)
if (rc)
return rc;
tsm->state = PCI_TSM_ACCEPT;
+ pdev->dev.tdi_enabled = true;
+
return 0;
}

@@ -557,6 +560,9 @@ static void __pci_tsm_init(struct pci_dev *pdev)
default:
break;
}
+
+ /* FIXME!! should this be default true and switch to false for TEE capable device */
+ pdev->dev.tdi_enabled = false;
}

void pci_tsm_init(struct pci_dev *pdev)
diff --git a/include/linux/device.h b/include/linux/device.h
index 4940db137fff..d62e0dd9d8ee 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -688,6 +688,7 @@ struct device {
#ifdef CONFIG_IOMMU_DMA
bool dma_iommu:1;
#endif
+ bool tdi_enabled:1;
};

/**
diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 3dae0f592063..61e7cff7768b 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -173,6 +173,10 @@ static inline bool is_swiotlb_force_bounce(struct device *dev)
{
struct io_tlb_mem *mem = dev->dma_io_tlb_mem;

+ if (dev->tdi_enabled) {
+ dev_warn_once(dev, "(TIO) Disable SWIOTLB");
+ return false;
+ }
return mem && mem->force_bounce;
}

--
2.43.0