Re: [PATCH v3 3/3] arm64: realm: Use aliased addresses for device DMA to shared buffers

On Thu, Feb 27, 2025 at 02:41:50PM +0000, Suzuki K Poulose wrote:

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_addr_{encrypted, canonical}
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: Marek Szyprowski <m.szyprowski@samsung.com>
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>

In case this goes in via the DMA API tree:

Acked-by: Catalin Marinas <catalin.marinas@arm.com>

(we could bikeshed on the names like unencrypted vs decrypted but I'm
not fussed about)