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

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Message-ID: <5c59d489-f9f9-4383-a90d-93badfb65291@redhat.com>
Date: Fri, 28 Feb 2025 12:08:19 +1000
From: Gavin Shan <gshan@...hat.com>
To: Suzuki K Poulose <suzuki.poulose@....com>, linux-kernel@...r.kernel.org
Cc: will@...nel.org, catalin.marinas@....com, maz@...nel.org,
 steven.price@....com, aneesh.kumar@...nel.org, robin.murphy@....com,
 linux-arm-kernel@...ts.infradead.org,
 Jean-Philippe Brucker <jean-philippe@...aro.org>,
 Christoph Hellwig <hch@....de>, Marek Szyprowski <m.szyprowski@...sung.com>,
 Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH v3 3/3] arm64: realm: Use aliased addresses for device DMA
 to shared buffers



On 2/28/25 12:41 AM, 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@...nel.org>
> Cc: Jean-Philippe Brucker <jean-philippe@...aro.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Robin Murphy <robin.murphy@....com>
> Cc: Steven Price <steven.price@....com>
> Cc: Christoph Hellwig <hch@....de>
> Cc: Marek Szyprowski <m.szyprowski@...sung.com>
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Cc: Aneesh Kumar K.V <aneesh.kumar@...nel.org>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> ---
> Changes since v2:
>   - Drop dma_addr_encrypted() helper, which is a NOP for CCA ( Aneesh )
>   - Only mask the "top" IPA bit and not all the bits beyond top bit. ( Robin )
>   - Use PROT_NS_SHARED, now that we only set/clear top bit. (Gavin)
> ---
>   arch/arm64/include/asm/mem_encrypt.h | 11 +++++++++++
>   1 file changed, 11 insertions(+)
> 

Reviewed-by: Gavin Shan <gshan@...hat.com>