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

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Date:	Fri, 5 Feb 2016 08:41:15 +0800
From:	Dave Young <dyoung@...hat.com>
To:	Matt Fleming <matt@...eblueprint.co.uk>
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 02/04/16 at 11:56am, Matt Fleming wrote:
> 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.

Ok, thanks.

> 
> > 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.

Thing is we support both kexec_load and kexec_file_load, if we do something
in kernel loader we will need do same in userspace kexec-tools as well.

Another way is we probably can retain the boot service areas for kexec
boot, but yes it is another special handling for kexec :(. Is this way
better to you?

Thanks
Dave