Re: [Patch] acpi: introduce "acpi_addr=" parameter for kdump

From: Cong Wang
Date: Mon Mar 21 2011 - 02:40:27 EST

Eric, any comments?

Matthew, seems you agree on this patch, may I have your ACK?


ä 2011å03æ11æ 02:50, Matthew Garrett åé:
On Thu, Mar 10, 2011 at 09:50:28AM -0800, Eric W. Biederman wrote:

Move all EFI calls that the kernel does (on x86) into a special section
of the bzImage that the bootloader can run. This works very well for
the x86 BIOS and it should also work very well for EFI. Among other
things by having a special 32bit and a special 64bit section this solves
the what flavor of EFI problem are we running on problem.

There's no benefit in calling any EFI methods in the kernel if we have
no intention of making further calls later. If we intent on making
further calls later then this approach doesn't work well.

Never perform any EFI calls once the kernel is initialized, last I
looked all of the EFI calls that were interesting to perform at runtime
were a subset of what ACPI can do, and ACPI is a easier to deal with
long term.

With the exception of reboot, I don't see any overlap between the EFI
runtime services and ACPI.

Kexec and kdump can easily pass the gather data from the first kernel to
the second kernel like we do for the normal bios paramsters today.

Doing that's not a problem. The real problem is that passing a virtual
map to EFI is a one-shot event. The information we need to provide to
the second kernel isn't a set of parameters - it's the whole memory map,
and we need to depend on the kernel to be able to set up the same map

As a fly in the ointment that leaves the question of how do we set EFI
variables. It is needed functionality when we are installing, and
occasionally nice to have. But it is a very rare slow path. I would
isolate the EFI after the kernel has booted to exactly to that one case.
Either with a special driver or a some flavor of virtualization from
userspace like we used to do for video card initialization.

Also capsule updating (not that we implement that at present, but
vendors will want it). But, again, if you want to push this out to some
sort of magic then we can just drop pretty much all of the kernel EFI

The current design of EFI in the x86 kernel is crap. We seem to have
advanced past the early adopter hack anything together to make it work
stage. So let's stop adding hacks and write something that won't give
us a long term support problems.

We're using EFI exactly as it's designed to be used at the moment. The
only problem is that nobody ever thought people would try to do anything
like booting one OS into another OS that has different ideas about
address space layout, but that's a problem with the spec and not our

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