Re: [PATCH v7 04/17] ARM64 / ACPI: Introduce early_param for "acpi" and pass acpi=force to enable ACPI

[Catalin Marinas]

On Wed, Jan 21, 2015 at 04:05:33PM +0000, Jon Masters wrote:
> On 01/21/2015 10:42 AM, Catalin Marinas wrote:
> > On Wed, Jan 21, 2015 at 03:29:52PM +0000, Jon Masters wrote:
> >> On 01/21/2015 10:23 AM, Catalin Marinas wrote:
> >>> I have some questions for the ACPI and EFI folk:
> >>>
> >>> 1. When booting with ACPI, are the EFI run-time services required for
> >>>    anything? If yes, Xen may have a bigger problem
> >>
> >> Yes. At least for some things. For example, installing an Operating
> >> System would require that you make runtime services calls to set the
> >> BootOrder/BootNext variables, and so on. Further, we use the GetTime
> >> service and EFI based reboot to avoid having special drivers. I had
> >> those added to SBBR as requirements for that reason.
> > 
> > So what would a kexec'ed kernel do here? Or we usually expect it to be
> > short lived and doesn't need reboot, nor GetTime.
> 
> In the use case that I have, it'll use EFI Runtime Servies to handle
> both the time of day (which it will need) and to subsequently reboot.
> This is currently being worked on (integration into kdump).

So the EFI run-time services (and EFI tables) will be preserved across
kexec? Could Xen not to something similar?

> >>> 2. Could a boot loader (either kernel doing kexec or Xen) emulate the
> >>>    EFI system/config tables and still make them useful to the kernel but
> >>>    without EFI_BOOT or EFI_RUNTIME_SERVICES?
> >>
> >> Yes. But again, without the other required pieces (including the
> >> services function pointers in the systab which are required) you'd crash
> >> soon after boot trying to make those calls.
> > 
> > My point was whether you can still pass information like RSDP address
> > via EFI tables but explicitly disable runtime services so that the
> > kernel won't try to make such calls (and crash).
> 
> Yes. As Graeme says, it works just to pass in the ACPI information and
> turn off EFI *BUT* it does not work to say you have EFI and then not
> provide the correct EFI services. To do so is out of spec, and in fact
> it's one reason we weren't able to turn the GetTime service on generally
> for x86 - some older x86 boxes didn't implement it originally (another
> reason on our end we're requiring all of these services on day one so
> that there won't be time for someone to miss them in firmware).

OK, thanks for confirming this. So the answer to my second question is
"not really".

-- 
Catalin
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