[PATCH 0/1] use RT_PROPERTIES table to implement efi=novamap

[Shawn Guo]

On Fri, Mar 05, 2021 at 10:39:57AM +0100, Ard Biesheuvel wrote:
> This patch addresses an oversight on my part when I implemented Linux
> side support for the EFI RT properties table: SetVirtualAddressMap() is
> itself a runtime service which is only callable at runtime to begin with,
> and so the EFI stub should only call it if it is not marked as unsupported.
> 
> This may be useful for the Snapdragon EFI based laptops, which already rely
> on a special EFI driver to expose the correct DT based on metadata exposed
> by EFI. These systems ship with a broken implementation of SetVirtualAddressMap,
> which is currently being worked around by passing efi=novamap on the kernel.
> command line.
> 
> After applying this patch (which I intend to propose for backporting to 5.10),
> the same can be achieved by exposing a RT_PROP table that marks SetVAMap() as
> unsupported. And while at it, better mark the variable services as unsupported
> as well, since they don't work under Linux either.
> 
> I'm open to extending this with a Linux specific override value kept in a
> EFI variable, so that platforms that cannot support DtbLoader are able to
> implement something similar.

Yes, that will be much appreciated!  IMHO, this is definitely an useful
addition, as DtbLoader shouldn't be mandated.  In some cases, people may
choose to load DTB with other means, or DTB is not required at all.
Yeah, ACPI kernel is already useful for these laptops, not only for
running installer but also as a console based native arm64 machine.

Looking forward to something for testing :)

Shawn