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

From: H. Peter Anvin
Date: Tue Sep 29 2015 - 21:04:53 EST

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.)


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