Re: [PATCH v5 4/4] MdePkg/BaseMemoryLibOptDxe ARM|AARCH64: disallow use in SEC & PEI phases

[Jeremy Linton <jeremy.linton@arm.com>]

Hi,

On 09/09/2016 09:00 AM, Ard Biesheuvel wrote:
> The new accelerated ARM and AARCH64 implementations take advantage of
> features that are only available when the MMU and Dcache are on. So
> restrict the use of this library to the DXE phase or later.

I don't think this is sufficient because DC ZVA doesn't work against 
device memory/etc. That means that users have to somehow know the 
page/etc attributes of memory regions before they call SetMemXX() on them.

I think this is a problem because nowhere in the UEFI specs do I see 
such restrictions on those memory operations.

For a specific problematic example, the LcdGraphicsOutputBlt.c uses it 
for BltVideoFill() and the target of that is likely not regular cached 
video memory.



>
> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
>  MdePkg/Library/BaseMemoryLibOptDxe/BaseMemoryLibOptDxe.inf | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/MdePkg/Library/BaseMemoryLibOptDxe/BaseMemoryLibOptDxe.inf b/MdePkg/Library/BaseMemoryLibOptDxe/BaseMemoryLibOptDxe.inf
> index 64d11b09ef06..5ddc0cbc2d77 100644
> --- a/MdePkg/Library/BaseMemoryLibOptDxe/BaseMemoryLibOptDxe.inf
> +++ b/MdePkg/Library/BaseMemoryLibOptDxe/BaseMemoryLibOptDxe.inf
> @@ -116,6 +116,15 @@ [Sources.X64]
>    X64/CopyMem.S
>    X64/IsZeroBuffer.nasm
>
> +[Defines.ARM, Defines.AARCH64]
> +  #
> +  # The ARM implementations of this library may perform unaligned accesses, and
> +  # may use DC ZVA instructions that are only allowed when the MMU and D-cache
> +  # are on. Since SEC, PEI_CORE and PEIM modules may execute with the MMU off,
> +  # omit them from the supported module types list for this library.
> +  #
> +  LIBRARY_CLASS = BaseMemoryLib|DXE_CORE DXE_DRIVER DXE_RUNTIME_DRIVER UEFI_DRIVER UEFI_APPLICATION
> +
>  [Sources.ARM]
>    Arm/ScanMem.S       |GCC
>    Arm/SetMem.S        |GCC
>