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

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

Aneesh Kumar K.V <aneesh.kumar@kernel.org> writes:

> 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?
>

Also translate_dma_to_phys/translate_phys_to_dma work with private dma
addr/alias right?

>
> 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 */