Re: Problem with Arm Mmu code in CpuDxe

[Kurt Kennett <Kurt.Kennett@microsoft.com>]

Also, if that comment was correct, why would the code directly check for a pagetable:

    } else if (TT_DESCRIPTOR_SECTION_TYPE_IS_PAGE_TABLE(FirstLevelTable[i])) {

I think maybe the comment was out of date.

K2

-----Original Message-----
From: Ard Biesheuvel [mailto:ard.biesheuvel@linaro.org] 
Sent: Wednesday, September 21, 2016 10:21 AM
To: Kurt Kennett <Kurt.Kennett@microsoft.com>
Cc: edk2-devel <edk2-devel@lists.01.org>
Subject: Re: [edk2] Problem with Arm Mmu code in CpuDxe

On 21 September 2016 at 17:09, Kurt Kennett <Kurt.Kennett@microsoft.com> wrote:
> I am having a problem on my system (assert), and during investigation I may have found a problem with the Arm CpuDxe Mmu code that may affect all ARM platform users.
>
> CpuDxeInitialize is the entry point, and pretty soon after entry it does:
>
>   SyncCacheConfig (&mCpu);
>
> This calls into:
>   ArmPkg\Drivers\CpuDxe\Arm\Mmu.c
>
> The code asserts that the Mmu is enabled, gets the memory space map, then starts to process the page tables by getting the TTBR0 base address.

Before the assert, there is a comment that says

  // This code assumes MMU is enabled and filed [sic] with section translations

I don't know if this is a reasonable thing to assume, and how you end up violating this assumption, but it does explain why the code does not work correctly.

What does your memory map look like?