linux-kernel - Re: [PATCH] x86, x86-64, gdt, hibernate: Store/load GDT for hibernate path.

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Message-ID: <20130502125000.GA5824@konrad-lan.dumpdata.com>
Date:	Thu, 2 May 2013 08:50:00 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Pavel Machek <pavel@....cz>
Cc:	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	rjw@...k.pl, tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	x86@...nel.org
Subject: Re: [PATCH] x86, x86-64, gdt, hibernate: Store/load GDT for
 hibernate path.

On Thu, May 02, 2013 at 02:34:38PM +0200, Pavel Machek wrote:
> Hi!
> 
> > The git commite7a5cd063c7b4c58417f674821d63f5eb6747e37
> > ("x86-64, gdt: Store/load GDT for ACPI S3 or hibernate/resume path
> > is not needed.") assumes that for the hibernate path the booting
> > kernel and the resuming kernel MUST be the same. That is certainly
> > the case for a 32-bit kernel (see check_image_kernel and
> > CONFIG_ARCH_HIBERNATION_HEADER config option).
> > 
> > However for 64-bit kernels it is OK to have a different kernel
> > version (and size of the image) of the booting and resuming kernels.
> > Hence the above mentioned git commit introduces an regression.
> 
> Ok.
> 
> > This patch fixes it by introducing a 'struct desc_ptr gdt_desc'
> > back in the 'struct saved_context'. However instead of having in the
> > 'save_processor_state' and 'restore_processor_state' the
> > store/load_gdt calls, we are only saving the GDT in the
> > save_processor_state.
> > 
> > For the restore path the lgdt operation is done in
> > hibernate_asm_[32|64].S in the 'restore_registers' path.
> 
> So the on-disk format changed and we need to bump the version number
> somewhere?

Fortunatly not. The patch (7a5cd063c7b4c58417f674821d63f5eb6747e37) that
just just landed in Linus a couple of days ago did change it a bit
(as the 'saved_context' struct shrunk), but this patch brings it back
to what it was before. But I don't know if the 'saved_context' structure
is actually somewhere specifically mentioned as 'on-disk' or in the
kernel.

Looking at the code, I think the on-disk structure you are referring to
is the 'struct restore_data_record' (please correct me if I am
incorrect) which has not been affected by any of these patches.

> 
> I guess we should add big fat warning to the affected structures.

We certainly can. I can prep a patch to that affect on Friday or Monday.
> 
> 								Pavel
> 
> -- 
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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