linux-kernel - Re: [PATCH] x86/efi: skip bgrt init for kexec reboot

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Date:	Thu, 4 Feb 2016 11:56:56 +0000
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Dave Young <dyoung@...hat.com>
Cc:	linux-efi@...r.kernel.org, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
	linux-acpi@...r.kernel.org,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Josh Triplett <josh@...htriplett.org>,
	Matthew Garrett <mjg59@...f.ucam.org>
Subject: Re: [PATCH] x86/efi: skip bgrt init for kexec reboot

On Thu, 04 Feb, at 07:09:03PM, Dave Young wrote:
> 
> Consider the original code path, maybe change it to efi_kexec_setup will
> be better to remind people? Or something else like a wraper function with
> similar name..

Possibly. I had considered adding a new efi_enabled() bit for
KEXEC_BOOT, but I'm worried that'll just encourage more uses.

The best approach is going to be to see whether we can reduce the uses
of efi_setup and the associated special code. Once we've completed
that exercise, we can think about the best name for this variable.

> For building ACPI tables we need do it in kernel instead of kexec-tools
> because of kexec_file_load for secure boot case so we still need a conditional
> code path for kexec..

Note that it may not be necessary to build any ACPI tables at all,
provided that things like acpi_get_table() fail gracefully for kexec.
I'm assuming that's the problem that you discovered when writing this
patch.

And yes, I don't expect you can build the ACPI table from userspace,
but it should at least be possible to do it in setup_boot_parameters()
or so when you setup the EFI table pointers (efi.config_tables), etc.
I think that would be a natural home for this feature.

> Also I'm not sure how to rebuild ACPI tables, it is easy or hard. Let me
> checking the detail and think more about it.

Thanks.