Re: [RFC] ArmPkg/ArmMmuLib: Add new attribute WRITE_BACK_NONSHARE

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 7 November 2017 at 11:05, Heyi Guo <heyi.guo@linaro.org> wrote:
> From: Peicong Li <lipeicong@huawei.com>
>
> Flash region needs to be set as cacheable (write back) to increase
> performance, if PEI is still XIP on flash or DXE FV is decompressed
> from flash FV. However some ARM platforms do not support to set flash
> as inner shareable since flash is not normal DDR memory and it will
> not respond to cache snoop request, which will causes system hang
> after MMU is enabled.
>
> So we need a new ARM memory region attribute WRITE_BACK_NONSHARE for
> flash region on these platforms specifically. This attribute will set
> the region as write back but not inner shared.
>
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Peicong Li <lipeicong@huawei.com>
> Signed-off-by: Heyi Guo <heyi.guo@linaro.org>
> Cc: Leif Lindholm <leif.lindholm@linaro.org>
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
>  ArmPkg/Include/Library/ArmLib.h                  | 2 ++
>  ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c | 4 ++++
>  2 files changed, 6 insertions(+)
>
> diff --git a/ArmPkg/Include/Library/ArmLib.h b/ArmPkg/Include/Library/ArmLib.h
> index 24ffe9f..e43e375 100644
> --- a/ArmPkg/Include/Library/ArmLib.h
> +++ b/ArmPkg/Include/Library/ArmLib.h
> @@ -39,6 +39,8 @@
>  typedef enum {
>    ARM_MEMORY_REGION_ATTRIBUTE_UNCACHED_UNBUFFERED = 0,
>    ARM_MEMORY_REGION_ATTRIBUTE_NONSECURE_UNCACHED_UNBUFFERED,
> +  ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK_NONSHARE,
> +  ARM_MEMORY_REGION_ATTRIBUTE_NONSECURE_WRITE_BACK_NONSHARE,
>    ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK,
>    ARM_MEMORY_REGION_ATTRIBUTE_NONSECURE_WRITE_BACK,
>    ARM_MEMORY_REGION_ATTRIBUTE_WRITE_THROUGH,
> diff --git a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
> index 8bd1c6f..cc10143 100644
> --- a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
> +++ b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
> @@ -35,6 +35,10 @@ ArmMemoryAttributeToPageAttribute (
>    )
>  {
>    switch (Attributes) {
> +  case ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK_NONSHARE:
> +  case ARM_MEMORY_REGION_ATTRIBUTE_NONSECURE_WRITE_BACK_NONSHARE:
> +    return TT_ATTR_INDX_MEMORY_WRITE_BACK;
> +
>    case ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK:
>    case ARM_MEMORY_REGION_ATTRIBUTE_NONSECURE_WRITE_BACK:
>      return TT_ATTR_INDX_MEMORY_WRITE_BACK | TT_SH_INNER_SHAREABLE;
> --
> 2.7.2.windows.1
>

I'd prefer the name
ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK_NONSHAREABLE but other than
that, this looks sensible to me. Leif?