Re: [PATCH v2 3/3] arm64: realm: Use aliased addresses for device DMA to shared buffers

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
+
+static inline dma_addr_t dma_encrypted(dma_addr_t daddr)
+{
+	if (is_realm_world())
+		daddr &= prot_ns_shared - 1;