Re: [PATCH v2 3/3] arm64: realm: Use aliased addresses for device DMA to shared buffers
From: Gavin Shan <hidden>
Date: 2025-02-25 05:24:51
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Hi Suzuki, On 2/20/25 8:07 AM, Suzuki K Poulose wrote:
quoted hunk ↗ jump to hunk
When a device performs DMA to a shared buffer using physical addresses, (without Stage1 translation), the device must use the "{I}PA address" with the top bit set in Realm. This is to make sure that a trusted device will be able to write to shared buffers as well as the protected buffers. Thus, a Realm must always program the full address including the "protection" bit, like AMD SME encryption bits. Enable this by providing arm64 specific dma_{encrypted,decrypted,clear_encryption} helpers for Realms. Please note that the VMM needs to similarly make sure that the SMMU Stage2 in the Non-secure world is setup accordingly to map IPA at the unprotected alias. Cc: Will Deacon <will@kernel.org> Cc: Jean-Philippe Brucker <redacted> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Robin Murphy <robin.murphy@arm.com> Cc: Steven Price <steven.price@arm.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Tom Lendacky <thomas.lendacky@amd.com> Cc: Aneesh Kumar K.V <aneesh.kumar@kernel.org> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com> --- arch/arm64/include/asm/mem_encrypt.h | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+)diff --git a/arch/arm64/include/asm/mem_encrypt.h b/arch/arm64/include/asm/mem_encrypt.h index f8f78f622dd2..aeda3bba255e 100644 --- a/arch/arm64/include/asm/mem_encrypt.h +++ b/arch/arm64/include/asm/mem_encrypt.h@@ -21,4 +21,26 @@ static inline bool force_dma_unencrypted(struct device *dev) return is_realm_world(); } +static inline dma_addr_t dma_decrypted(dma_addr_t daddr) +{ + if (is_realm_world()) + daddr |= prot_ns_shared; + return daddr; +} +#define dma_decrypted dma_decrypted +
There is an existing macro (PROT_NS_SHARED), which is preferred to return prot_ns_shared or 0 depending on the availability of the realm capability. However, that macro needs to be improved a bit so that it can be used here. We need to return 0UL to match with the type of prot_ns_shared (unsigned long) -#define PROT_NS_SHARED (is_realm_world() ? prot_ns_shared : 0) +#define PROT_NS_SHARED (is_realm_world() ? prot_ns_shared : 0UL) After that, the chunk of code can be as below. return daddr | PROT_NS_SHARED;
+static inline dma_addr_t dma_encrypted(dma_addr_t daddr)
+{
+ if (is_realm_world())
+ daddr &= prot_ns_shared - 1;
+ return daddr;
+}
+#define dma_encrypted dma_encrypted
+With PROT_NS_SHARED, it can become something like below. (PROT_NS_SHARED - 1) is equivalent to -1UL, 'daddr & -1UL' should be fine since it does nothing. return daddr & (PROT_NS_SHARED - 1);
+static inline dma_addr_t dma_clear_encryption(dma_addr_t daddr)
+{
+ return dma_encrypted(daddr);
+}
+#define dma_clear_encryption dma_clear_encryption
+
#endif /* __ASM_MEM_ENCRYPT_H */Thanks, Gavin