On Tue, Sep 29, 2015 at 6:03 PM, H. Peter Anvin [off-list ref] wrote:

On 09/27/2015 12:06 AM, Ingo Molnar wrote:

quoted

* Ard Biesheuvel [off-list ref] wrote:

quoted

quoted

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.

--Andy