Subject: Re: efi_enabled(EFI_PARAVIRT) use

From: Matt Fleming <[email-masked]>
Date: Fri, 29 Apr 2016 15:39:31 +0100

On Fri, 29 Apr, at 11:34:45AM, Stefano Stabellini wrote:
> On Fri, 29 Apr 2016, Ingo Molnar wrote:
> > Also, it would be nice to have all things EFI in a single tree, the conflicts are 
> > going to be painful! There's very little reason not to carry this kind of commit:
> > 
> >  arch/arm/xen/enlighten.c           |  6 +++++
> >  drivers/firmware/efi/arm-runtime.c | 17 +++++++++-----
> >  drivers/firmware/efi/efi.c         | 45 ++++++++++++++++++++++++++++++++------
> >  3 files changed, 56 insertions(+), 12 deletions(-)
> > 
> > in the EFI tree.
> 
> That's true. I'll drop this commit from xentip and let Matt pick it up
> or request changes as he sees fit.

One small change I think would be sensible to make is to expand
EFI_PARAVIRT into a few more bits to clearly indicate the quirks on
Xen, and in the process, to delete EFI_PARAVIRT.

That should address Ingo's major concern, and also make it much easier
to rework the code in a piecemeal fashion.

Could somebody enumerate the things that make Xen (dom0) different on
arm* compared with bare metal EFI boot? The list I made for x86 was,

  1. Has no EFI memory map
  2. Runtime regions do not need to be mapped
  3. Cannot call SetVirtualAddressMap()
  4. /sys/firmware/efi/fw_vendor is invisible

The first maps to not setting EFI_MEMMAP, the second to not setting
EFI_RUNTIME. If we add EFI_ALREADY_VIRTUAL and EFI_FW_VENDOR_INVISIBLE
to efi.flags that should cover everything on x86. Does arm* require
anything else?