linux-kernel - Re: [PATCH 0/3] Fix ACPI BGRT support for images located in EFI boot services memory

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Message-ID: <20120904194523.GA5064@jtriplet-mobl1>
Date:	Tue, 4 Sep 2012 12:45:23 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Matt Fleming <matt.fleming@...el.com>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	Len Brown <lenb@...nel.org>, Olof Johansson <olof@...om.net>,
	Matthew Garrett <mjg@...hat.com>,
	David Howells <dhowells@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Jim Cromie <jim.cromie@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Pawel Moll <pawel.moll@....com>, linux-acpi@...r.kernel.org,
	linux-efi <linux-efi@...r.kernel.org>
Subject: Re: [PATCH 0/3] Fix ACPI BGRT support for images located in EFI boot
 services memory

On Tue, Sep 04, 2012 at 11:10:54AM -0700, H. Peter Anvin wrote:
> On 09/04/2012 10:59 AM, Josh Triplett wrote:
> >
> >Unfortunately not.  We need enough of ACPI available to go read the
> >BGRT to know what to copy, so we need to defer freeing boot services
> >code until after we initialize ACPI (and thus everything ACPI needs,
> >which includes EFI since ACPI looks for root tables there).
> >
> >>I wouldn't be surprised if some implementations got really cranky if
> >>we accessed boot services data after we installed a new virtual memory
> >>map.
> >
> >Note that I've carefully accessed the boot services data *through* the
> >new virtual memory map, which should work fine.
> >
> 
> There are some platforms which have bugs in this area, so there are
> other reasons to defer freeing up boot memory until as late in the
> boot process as we can possibly get away with.
> 
> free_initmem() is presuambly the place that makes most sense.

You're suggesting a call from free_initmem() to
efi_free_boot_services()?  Or, from init_post() right before the call to
free_initmem()?

> This
> is EFI-specific but not x86-specific, let's not commingle those
> concepts, please...

init/main.c already calls the x86-specific efi_enter_virtual_mode
(defined in arch/x86/platform/efi/efi.c), and I split the call to the
x86-specific efi_free_boot_services out of that.  Neither of those
functions exists on non-x86 platforms, and thus I mirrored the #ifdef
currently wrapped around efi_enter_virtual_mode for the new call to
efi_free_boot_services.  While it might make sense for that code to
exist on non-x86 EFI platforms, it currently doesn't.  At best, I could
add static inline stubs to linux/efi.h for those functions to avoid the
ifdefs, but as far as I can tell the same issue applies to quite a few
more functions in efi.h.

Would you like me to add the static inline stubs for the couple of
functions called from init/main.c, or leave the #ifdefs?

- Josh Triplett
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