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From: "Ard Biesheuvel" <ardb@kernel.org>
Date: Tue, 6 Sep 2022 19:53:53 +0200
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Subject: Re: [edk2-devel] [PATCH 0/2] Add support EFI_MP_SERVICES_PROTOCOL on AARCH64
To: devel@edk2.groups.io, quic_rcran@quicinc.com
Cc: Leif Lindholm <quic_llindhol@quicinc.com>, Ard Biesheuvel <ardb+tianocore@kernel.org>, 
	Sami Mujawar <sami.mujawar@arm.com>, Jian J Wang <jian.j.wang@intel.com>, 
	Liming Gao <gaoliming@byosoft.com.cn>
Content-Type: text/plain; charset="UTF-8"

On Tue, 6 Sept 2022 at 19:01, Rebecca Cran <quic_rcran@quicinc.com> wrote:
>
> On 9/5/22 09:55, Ard Biesheuvel wrote:
> > I think you've got things covered: I suggested RPi4 because it uses
> > A72, and I seem to remember the issues I observed were either on A57
> > or A72 (which are quite similar). But between Juno and HoneyComb, I
> > don't think the RPi4 data point is that useful.
>
> My only concern is about the call in MpServicesTest:
>
> WriteBackDataCacheRange ((VOID *)&ApFunction, 32);
>
> Obviously the '32' is a magic number and should be something based on the size of ApFunction.
> But I don't think there's a portable way to calculate what that value should be.
>

Why exactly do we need that call?

I understand that some of the code needs to be clean to the PoC (on
ARM) so that the AP can fetch instructions with the MMU and caches
disabled. But the actual routine passed into the API is called with
the MMU and caches on, right?