Re: [PATCH 2/2] arm64/efi: Don't pad between EFI_MEMORY_RUNTIME regions

From: Andy Lutomirski
Date: Tue Sep 29 2015 - 21:16:50 EST

On Tue, Sep 29, 2015 at 6:03 PM, H. Peter Anvin <hpa@xxxxxxxxx> wrote:
> On 09/27/2015 12:06 AM, Ingo Molnar wrote:
>> * Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> wrote:
>>>> If we allocate the EFI runtime as a single virtual memory block then issues
>>>> like rounding between sections does not even come up as a problem: we map the
>>>> original offsets and sizes byte by byte.
>>> Well, by that reasoning, we should not call SetVirtualAddressMap() in the first
>>> place, and just use the 1:1 mapping UEFI uses natively. This is more than
>>> feasible on arm64, and I actually fought hard against using
>>> SetVirtualAddressMap() at all, but I was overruled by others. I think this is
>>> also trivially possible on X64, since the 1:1 mapping is already active
>>> alongside the VA mapping.
>> Could we please re-list all the arguments pro and contra of 1:1 physical mappings,
>> in a post that also explains the background so that more people can chime in, not
>> just people versed in EFI internals? It's very much possible that a bad decision
>> was made.
> Pro: by far the sanest way to map the UEFI tables.
> Con: doesn't actually work (breaks on several known platforms.)

Can we at least do 1:1 without an offset on arm64? Given that Linux
seems to be more of a reference on arm64 than Windows is, maybe that
would give everyone something vaguely sane to work with.

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