Re: [PATCH 1/1] arm64: realm: Use aliased addresses for device DMA to shared buffers

[Aneesh Kumar K.V <aneesh.kumar@kernel.org>]

Suzuki K Poulose <suzuki.poulose@arm.com> writes:

> 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@kernel.org>
> Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>
> 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>
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.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));
>  }
>  
>  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 */
>  
> -- 
> 2.43.0

How about the below?

The function name addr_to_shared is too generic to be included in the
dma-direct.h header file. Since we don’t expect it to be called
directly, we can either inline it or find a more specific name.

Additionally, for dma_to_phys conversion, we first retrieve the private
address/alias before switching to the physical address. While both
approaches yield the correct result, this change more clearly defines the
conversion rules?

modified   arch/arm64/include/asm/dma-direct.h
@@ -4,14 +4,14 @@
 
 #include <asm/pgtable-prot.h>
 
-static inline unsigned long addr_to_shared(unsigned long addr)
+static inline unsigned long shared_dma_addr(unsigned long addr)
 {
 	if (is_realm_world())
 		addr |= prot_ns_shared;
 	return addr;
 }
 
-static inline unsigned long addr_to_private(unsigned long addr)
+static inline unsigned long private_dma_addr(unsigned long addr)
 {
 	if (is_realm_world())
 		addr &= prot_ns_shared - 1;
@@ -26,13 +26,14 @@ static inline dma_addr_t phys_to_dma(struct device *dev, phys_addr_t 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));
+	return shared_dma_addr(__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));
+	/* if it is a shared dma addr convert to private before looking for phys_addr */
+	return __dma_to_phys(dev, private_dma_addr(dma_addr));
 }
 
 #endif	/* __ASM_DMA_DIRECT_H */