Re: EFI mode after running kexec

[James Bottomley <James.Bottomley-d9PhHud1JfjCXq6kfMZ53/egYHeGw8Jk@public.gmane.org>]

On Thu, 2013-08-29 at 08:18 -0400, Josh Boyer wrote:
> On Wed, Aug 28, 2013 at 10:26 PM, Greg KH <gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org> wrote:
> > Hi all,
> >
> > I've been messing with UEFI booting a kernel and then later on, using
> > kexec to boot another kernel, and noticed that the kexec'ed kernel is
> > not really in EFI mode, although the EFI framebuffer seems present and
> > able to be used.
> >
> > Is this to be expected?  I'd think that the EFI framebuffer wouldn't be
> > around anymore.  Odds are this is a BIOS bug, given that the machine I'm
> > using is a really old UEFI mode (i.e. before secure boot mode ever
> > showed up), but should it work this way?
> 
> AFAIK, it's to be expected at this point.  kexec doesn't work as it
> should with UEFI.  I believe Matthew and/or Matt can elaborate
> further, but it has to do with only being able to call
> ExitBootServices once and providing mappings to the UEFI Runtime
> services functions.

There's also the SetVirtualAddressMap() problem ...

> > And, to get kexec to run the kernel in EFI mode, would require kexec to
> > treat the kernel as a EFI binary and run it that way, instead of the
> > "normal" way it currently is, right?
> 
> I think so.

There are two ways we boot a kernel in EFI mode: one is with
BootServices intact (because the bootloader didn't call
ExitBootServices()) which is becoming more common and the other with
only RunTime Services.  The best that can be hoped for in kexec is the
latter, since it's practically impossible to reinitialise the
BootServices once they've been trashed.

James