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Re: [Xen-devel] [PATCH V2 for-4.5] EFI: Always use EFI command line

On Wed, Oct 29, 2014 at 9:55 AM, Daniel Kiper <daniel.kiper@xxxxxxxxxx> wrote:
> On Wed, Oct 29, 2014 at 03:26:40PM +0000, Ian Campbell wrote:
>> On Wed, 2014-10-29 at 13:44 +0100, Daniel Kiper wrote:
>> > On Tue, Oct 28, 2014 at 08:23:48PM -0700, Roy Franz wrote:
>> > > If possible I'd like to get this settled so that adjustments to the
>> > > EFI boot code can be made for the 4.5 release. It would be nice to
>> > > have the EFI boot from GRUB interface be settled and not change
>> > > after the release.
>> >
>> > Hmmm... Do you mean 4.6? 4.5 is in freezing state so only bugfixes are 
>> > allowed.
>> >
>> It would be a bug to release Xen on ARM 4.5 with broken handling of the
>> provision of the command line when booted via EFI.
> What is wrong with current implementation? I thought that it works
> in the same way on x86 and ARM. However, maybe I missing something.
> Daniel

I'll try to provide a brief summary.

Currently, when booted from GRUB, arm64 EFI Xen:
1) processes the EFI command line for EFI related options (-basevideo,
etc), ie those before the "--"
2) expects the Xen commandline to be in the GRUB provided FDT.
Anything past a "--" on the
    EFI commandline that would be given to Xen when booted natively
from EFI is ignored.

The GRUB work to support EFI Xen booting on arm64 is in progress, and
when Leif was reviewing
the code he noticed that this diverged from how EFI Linux was booted.
EFI Linux takes it's commandline
via the EFI commandline - GRUB does not put it in the FDT.  For the
EFI case, having both Xen and Linux
accept their commandlines the same way allows more shared code in
GRUB.  This is what motivated this
patch to change where the commandline was taken from.

The discussion of this patch brought up the related issue of how EFI
boot code specific options, and the
handling of the "--" separator.  This I think has been resolved -
there is no use for EFI boot specific options
when booting from GRUB, as the EFI boot code should not do anything
that requires configuration.  Therefore
there is no "--" required, and GRUB just deals with the Xen
commandline.  (Note that there are some small changes
required to remove some code from the GRUB boot case.)

So the open question is, when booted from GRUB (or other bootloader),
should Xen get it's commandline via the EFI
commandline, or via the MB2 protocol?  (and for arm64, this means the
FDT based multiboot.)  I felt that the shared code
in GRUB was a reasonable reason to follow what Linux did in the EFI case.


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