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Date: Tue, 30 Apr 2013 20:48:15 -0400
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org,
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Subject: Re: [tip:x86/paravirt] x86-64, gdt: Store/ load GDT for ACPI S3 or
 hibernate/resume path is not needed.
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On Wed, May 01, 2013 at 12:38:17AM +0200, Rafael J. Wysocki wrote:
> On Tuesday, April 30, 2013 05:25:42 PM Konrad Rzeszutek Wilk wrote:
> > > > After the 'restore_registers' it returns and we end up called
> > > > restore_processor_state() - where we reload the GDT. The reload of
> > > > the GDT is not needed as bootup kernel has already loaded the GDT which
> > > > is at the same physical location as the the restored kernel.
> > > 
> > > I'm not sure if this particular statement is actually correct.  It is correct
> > > on 32-bit, but here it is not necessary for the bootup kernel to be the same
> > > as the image one.  Different kernel version may be used for that even (at
> > > least theoretically).  So the question is, and I'm quite unsure about the
> > > answer, if the GDT of from the bootup kernel is really *guaranteed* to be
> > > at the same location (given that those kernels may be really different).
> > 
> > A bit of testing with different bootup kernel provided me with this error:
> > PM: Image mismatch: version
> 
> This implies that you tested on an architechture without
> CONFIG_ARCH_HIBERNATION_HEADER.
> 
> > which after a bit of digging pointed me to 'check_image_kernel'. The criteria
> > there imply that the different kernel versions or releases cannot be used with
> > hibernation.
> 
> Only if CONFIG_ARCH_HIBERNATION_HEADER is unset, which is not the case for
> CONFIG_X86_64.

OK, Let me play on 64-bit later on this week and see if the patch I cobbled up
to save/restore the GDT in the booting kernel properly works.