Subject: Re: [Regression] "x86-64/efi: Use EFI to deal with platform wall
 clock" prevents my machine from booting
From: Matt Fleming <matt.fleming@intel.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Ingo Molnar <mingo@kernel.org>, Matthew Garrett <mjg59@srcf.ucam.org>,
        linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org,
        cJ-ko@zougloub.eu, "H. PeterAnvin" <hpa@zytor.com>
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Organization: Intel Corporation (UK) Ltd. - Registered No. 1134945 - Pipers
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Date: Thu, 09 Aug 2012 09:51:35 +0100
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On Tue, 2012-08-07 at 11:50 +0100, Jan Beulich wrote:
> > 
> > I managed to find a machine to reproduce this on and it looks like the
> > ASUS firmware engineers are upto their old tricks of referencing
> > physical addresses after we've taken control of the memory map,
> 
> Yippie. On such systems we simply can't do any runtime calls.
> Should we add a command line option forcing efi_native to false,
> thus suppressing all runtime calls? Or would the "noefi" one be
> enough already?

I think a better solution for this, seeing as there appear to be *so*
many ASUS machines in the wild with this inability to do virtual EFI
calls, is to provide a 1:1 mapping as well as our regular virt->phys
mapping for the benefit of the firmware. We can load our special page
table in efi_call_*, etc.

One thing to note is that because of breakage seen on Apple machines
last time Matthew tried this approach, we (the kernel) can't actually
access the 1:1 mapping, it would exist purely for the benefit of
firmware that was broken enough to reference physical addresses after
SetVirtualAddressMap().

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