Re: [PATCH] ArmVirtPkg/ArmVirtQemu: use non-accelerated CopyMem for VariableRuntimeDxe

[Laszlo Ersek <lersek@redhat.com>]

On 11/14/17 11:22, Ard Biesheuvel wrote:
> The VariableRuntimeDxe driver may use CopyMem () on NOR flash regions,
> assuming such regions always have full memory semantics. Given that
> those regions cannot be mapped as ordinary memory on ARM (due to the
> fact that the NOR flash requires device semantics while in write mode)
> this prevents us from using BaseMemoryLibOptDxe in VariableRuntimeDxe,
> since it may use unaligned accesses and/or DC ZVA instructions, both
> of which are incompatible with mappings using device semantics.
> 
> Note that there is no way we can work around this by changing the
> mapping type between 'memory' and 'device' when switching from read to
> write mode and back, because the runtime mapping is created by the OS,
> and cannot be changed at will.
> 
> So let's just switch to the unaccelerated version of BaseMemoryLib which
> does not have the same problem.
> 
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
>  ArmVirtPkg/ArmVirtQemu.dsc       | 2 ++
>  ArmVirtPkg/ArmVirtQemuKernel.dsc | 2 ++
>  2 files changed, 4 insertions(+)
> 
> diff --git a/ArmVirtPkg/ArmVirtQemu.dsc b/ArmVirtPkg/ArmVirtQemu.dsc
> index 8a60b61f2aa6..7b220d6e3c31 100644
> --- a/ArmVirtPkg/ArmVirtQemu.dsc
> +++ b/ArmVirtPkg/ArmVirtQemu.dsc
> @@ -261,6 +261,8 @@ [Components.common]
>    MdeModulePkg/Universal/Variable/RuntimeDxe/VariableRuntimeDxe.inf {
>      <LibraryClasses>
>        NULL|MdeModulePkg/Library/VarCheckUefiLib/VarCheckUefiLib.inf
> +      # don't use unaligned CopyMem () on the UEFI varstore NOR flash region
> +      BaseMemoryLib|MdePkg/Library/BaseMemoryLib/BaseMemoryLib.inf
>    }
>  !if $(SECURE_BOOT_ENABLE) == TRUE
>    MdeModulePkg/Universal/SecurityStubDxe/SecurityStubDxe.inf {
> diff --git a/ArmVirtPkg/ArmVirtQemuKernel.dsc b/ArmVirtPkg/ArmVirtQemuKernel.dsc
> index 9a31ec93ca06..7c032e1b07e0 100644
> --- a/ArmVirtPkg/ArmVirtQemuKernel.dsc
> +++ b/ArmVirtPkg/ArmVirtQemuKernel.dsc
> @@ -252,6 +252,8 @@ [Components.common]
>    MdeModulePkg/Universal/Variable/RuntimeDxe/VariableRuntimeDxe.inf {
>      <LibraryClasses>
>        NULL|MdeModulePkg/Library/VarCheckUefiLib/VarCheckUefiLib.inf
> +      # don't use unaligned CopyMem () on the UEFI varstore NOR flash region
> +      BaseMemoryLib|MdePkg/Library/BaseMemoryLib/BaseMemoryLib.inf
>    }
>  !if $(SECURE_BOOT_ENABLE) == TRUE
>    MdeModulePkg/Universal/SecurityStubDxe/SecurityStubDxe.inf {
> 

Reviewed-by: Laszlo Ersek <lersek@redhat.com>

Given that we've never seen the symptom reported by Shannon, I must
think Shannon is using some kind of new hardware. May I ask what
hardware that is?

Thanks,
Laszlo