linux-kernel - Re: [PATCH] x86-64: use EFI to deal with platform wall clock

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Date:	Tue, 15 May 2012 14:19:07 +0100
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Matthew Garrett" <mjg59@...f.ucam.org>
Cc:	<mingo@...e.hu>, <tglx@...utronix.de>,
	<matt.fleming@...ux.intel.com>, <linux-kernel@...r.kernel.org>,
	<hpa@...or.com>
Subject: Re: [PATCH] x86-64: use EFI to deal with platform wall clock

>>> On 15.05.12 at 14:47, Matthew Garrett <mjg59@...f.ucam.org> wrote:
> On Tue, May 15, 2012 at 01:18:19PM +0100, Jan Beulich wrote:
> 
>> Simply removing the #ifdef around the respective code isn't enough,
>> however: The runtime code must not only be forced to be executable, it
>> also must have a proper virtual address set (which on at least the
>> system I'm testing on isn't the case for all necessary regions, or at
>> least not as early as they're now being required).
> 
> I don't understand this. The get_time pointer won't be updated to the 
> virtual function until the end of efi_enter_virtual_mode, at which point 
> all runtime regions should have a virtual address mapped. We also call 
> runtime_code_page_mkexec() immediately after updating that pointer, 
> although maybe the order should be swapped. So I think the bug you're 
> fixing is not the bug you think you're fixing...

I would have expected that things work that way, but they
don't. In particular is the function in efi_64.c that's being
modified here called from efi_call_phys_{pro,epi}log(), and at
that point we can't expect virtual addresses to be uniformly
set yet. So it's a physical call that requires the fixup done
here, as efi_set_executable() simply expects ->virt_addr to
be valid. I suspect that no physical calls other than
phys_efi_set_virtual_address_map() were being done so far
at all on 64-bit, hiding the problem.

Jan

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