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Message-ID: <7ebe959b-132e-468a-bad5-5273427b6928@arm.com>
Date: Wed, 12 Feb 2025 18:18:15 +0000
From: Robin Murphy <robin.murphy@....com>
To: Suzuki K Poulose <suzuki.poulose@....com>, will@...nel.org,
maz@...nel.org, catalin.marinas@....com
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
gregkh@...uxfoundation.org, aneesh.kumar@...nel.org, steven.price@....com,
Jean-Philippe Brucker <jean-philippe@...aro.org>,
Christoph Hellwig <hch@....de>, Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH 1/1] arm64: realm: Use aliased addresses for device DMA to
shared buffers
On 2025-02-12 5:14 pm, 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.
>
> Add the support for this by providing arm64 version of the phys_to_dma(). We
> cannot use the __sme_mask as it assumes the "encryption" always "sets a bit",
> which is the opposite for CCA. i.e., "set a bit" for "decrypted" address. So,
> move the common code that can be reused by all - i.e., add __phys_to_dma() and
> __dma_to_phys() - and do the arch specific processing.
>
> 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: Tom Lendacky <thomas.lendacky@....com>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> ---
> arch/arm64/Kconfig | 1 +
> arch/arm64/include/asm/dma-direct.h | 38 +++++++++++++++++++++++++++++
> include/linux/dma-direct.h | 35 +++++++++++++++++---------
> 3 files changed, 62 insertions(+), 12 deletions(-)
> create mode 100644 arch/arm64/include/asm/dma-direct.h
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index fcdd0ed3eca8..7befe04106de 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -41,6 +41,7 @@ config ARM64
> select ARCH_HAS_NMI_SAFE_THIS_CPU_OPS
> select ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE
> select ARCH_HAS_NONLEAF_PMD_YOUNG if ARM64_HAFT
> + select ARCH_HAS_PHYS_TO_DMA
> select ARCH_HAS_PTE_DEVMAP
> select ARCH_HAS_PTE_SPECIAL
> select ARCH_HAS_HW_PTE_YOUNG
> diff --git a/arch/arm64/include/asm/dma-direct.h b/arch/arm64/include/asm/dma-direct.h
> new file mode 100644
> index 000000000000..37c3270542b8
> --- /dev/null
> +++ b/arch/arm64/include/asm/dma-direct.h
> @@ -0,0 +1,38 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +#ifndef __ASM_DMA_DIRECT_H
> +#define __ASM_DMA_DIRECT_H
> +
> +#include <asm/pgtable-prot.h>
> +
> +static inline unsigned long addr_to_shared(unsigned long addr)
> +{
> + if (is_realm_world())
> + addr |= prot_ns_shared;
> + return addr;
> +}
> +
> +static inline unsigned long addr_to_private(unsigned long addr)
> +{
> + if (is_realm_world())
> + addr &= prot_ns_shared - 1;
> + return addr;
> +}
> +
> +static inline dma_addr_t phys_to_dma(struct device *dev, phys_addr_t paddr)
> +{
> + return __phys_to_dma(dev, paddr);
> +}
> +
> +static inline dma_addr_t phys_to_dma_unencrypted(struct device *dev,
> + phys_addr_t paddr)
> +{
> + return addr_to_shared(__phys_to_dma(dev, paddr));
> +}
> +#define phys_to_dma_unencrypted phys_to_dma_unencrypted
> +
> +static inline phys_addr_t dma_to_phys(struct device *dev, dma_addr_t dma_addr)
> +{
> + return addr_to_private(__dma_to_phys(dev, dma_addr));
> +}
> +
> +#endif /* __ASM_DMA_DIRECT_H */
> diff --git a/include/linux/dma-direct.h b/include/linux/dma-direct.h
> index d7e30d4f7503..3e9bf6ca640e 100644
> --- a/include/linux/dma-direct.h
> +++ b/include/linux/dma-direct.h
> @@ -72,18 +72,36 @@ static inline dma_addr_t dma_range_map_max(const struct bus_dma_region *map)
> return ret;
> }
>
> +static inline dma_addr_t __phys_to_dma(struct device *dev, phys_addr_t paddr)
> +{
> + if (dev->dma_range_map)
> + return translate_phys_to_dma(dev, paddr);
> + return paddr;
> +}
> +
> +static inline phys_addr_t __dma_to_phys(struct device *dev, dma_addr_t dma_addr)
> +{
> + phys_addr_t paddr;
> +
> + if (dev->dma_range_map)
> + paddr = translate_dma_to_phys(dev, dma_addr);
> + else
> + paddr = dma_addr;
> +
> + return paddr;
> +}
> +
> #ifdef CONFIG_ARCH_HAS_PHYS_TO_DMA
> #include <asm/dma-direct.h>
> #ifndef phys_to_dma_unencrypted
> #define phys_to_dma_unencrypted phys_to_dma
> #endif
> #else
> +
> static inline dma_addr_t phys_to_dma_unencrypted(struct device *dev,
> phys_addr_t paddr)
> {
> - if (dev->dma_range_map)
> - return translate_phys_to_dma(dev, paddr);
> - return paddr;
> + return __phys_to_dma(dev, paddr);
> }
>
> /*
> @@ -94,19 +112,12 @@ static inline dma_addr_t phys_to_dma_unencrypted(struct device *dev,
> */
> static inline dma_addr_t phys_to_dma(struct device *dev, phys_addr_t paddr)
> {
> - return __sme_set(phys_to_dma_unencrypted(dev, paddr));
> + return __sme_set(__phys_to_dma(dev, paddr));
Hmm, it really feels like we should generalise __sme_{set,clr} at this
level, rather than drag in the entire ARCH_HAS_PHYS_TO_DMA override for
the purposes of setting/clearing an address bit just because the
"generic" mechanism for doing that is unashamedly AMD-specific.
Maybe something like:
#define dma_shared(x) sme_clr(x)
#define dma_private(x) sme_set(x)
for x86, then go from there?
Thanks,
Robin.
> }
>
> static inline phys_addr_t dma_to_phys(struct device *dev, dma_addr_t dma_addr)
> {
> - phys_addr_t paddr;
> -
> - if (dev->dma_range_map)
> - paddr = translate_dma_to_phys(dev, dma_addr);
> - else
> - paddr = dma_addr;
> -
> - return __sme_clr(paddr);
> + return __sme_clr(__dma_to_phys(dev, dma_addr));
> }
> #endif /* !CONFIG_ARCH_HAS_PHYS_TO_DMA */
>
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