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Mon, 24 Feb 2025 21:28:31 -0800 (PST) Received: from [192.168.68.55] ([180.233.125.164]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2230a0a798asm5232455ad.189.2025.02.24.21.28.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 24 Feb 2025 21:28:30 -0800 (PST) Message-ID: <308f8a08-a6f8-403e-a130-18c7d3db2e23@redhat.com> Date: Tue, 25 Feb 2025 15:28:24 +1000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 3/3] arm64: realm: Use aliased addresses for device DMA to shared buffers From: Gavin Shan To: Suzuki K Poulose , will@kernel.org, robin.murphy@arm.com, catalin.marinas@arm.com Cc: maz@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, gregkh@linuxfoundation.org, aneesh.kumar@kernel.org, steven.price@arm.com, Jean-Philippe Brucker , Christoph Hellwig , Tom Lendacky References: <20250219220751.1276854-1-suzuki.poulose@arm.com> <20250219220751.1276854-4-suzuki.poulose@arm.com> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2/25/25 3:24 PM, Gavin Shan wrote: > On 2/20/25 8:07 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_{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 >> Cc: Jean-Philippe Brucker >> Cc: Catalin Marinas >> Cc: Robin Murphy >> Cc: Steven Price >> Cc: Christoph Hellwig >> Cc: Tom Lendacky >> Cc: Aneesh Kumar K.V >> Signed-off-by: Suzuki K Poulose >> --- >>   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. > I meant (PROT_NS_SHARED - 1) is equivalent to -1UL when no realm capability is around :) >     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