On 21 January 2015 at 21:46, Catalin Marinas [off-list ref] wrote:

On Wed, Jan 21, 2015 at 04:05:33PM +0000, Jon Masters wrote:

quoted

On 01/21/2015 10:42 AM, Catalin Marinas wrote:

quoted

On Wed, Jan 21, 2015 at 03:29:52PM +0000, Jon Masters wrote:

quoted

On 01/21/2015 10:23 AM, Catalin Marinas wrote:

quoted

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?

quoted

quoted

quoted

quoted

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).

This is the use case i am talking about, we have a wroking setup with
efi disabled
and rsdp passed via dtb, right now its done by adding a "rsdp" field
in the chosen node.
Do we have a formal way to pass RSDP without EFI? if not, it would be
good to have dtb binding
which we can use to pass RSDP address to kernel for ACPI.

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

--
Catalin