On Sat 2007-08-25 22:42:05, Rafael J. Wysocki wrote:

On Saturday, 25 August 2007 20:27, Rafael J. Wysocki wrote:

quoted

On Friday, 24 August 2007 22:46, Pavel Machek wrote:

quoted

Hi!

quoted

From: Rafael J. Wysocki <redacted>

Make it possible to restore a hibernation image on x86_64 with the help of a
kernel different from the one in the image.

The idea is to split the core restoration code into two separate parts and to
place each of them in a different page.  The first part belongs to the boot

What happens in case where both parts want to be
at the same place? (Like kernel being restored is 4KB smaller, so that
routines now collide?)

Bad things, but I can't see how to avoid that reliably.

Below is an analogous patch without this problem.  The slightly ugly thing
about it is that all pages in the temporary mapping have the NX bit cleard
now, so that we can run some code out of one of them.  Still, IMO, that isn't
really important, because the temporary page tables are dropped as soon as
we jump to restore_registers.

Greetings,
Rafael

---
From: Rafael J. Wysocki <redacted>

Make it possible to restore a hibernation image on x86_64 with the help of a
kernel different from the one in the image.

The idea is to split the core restoration code into two separate parts and to
place each of them in a different page.  The first part belongs to the boot
kernel and is executed as the last step of the image kernel's memory restoration
procedure.  Before being executed, it is relocated to a safe page that won't be
overwritten while copying the image kernel pages.

The final operation performed by it is a jump to the second part of the core
restoration code that belongs to the image kernel and has just been restored.
This code makes the CPU switch to the image kernel's page tables and
restores the state of general purpose registers (including the stack pointer)
from before the hibernation.

The main issue with this idea is that in order to jump to the second part of the
core restoration code the boot kernel needs to know its address.  However, this
address may be passed to it in the image header.  Namely, the part of the image
header previously used for checking if the version of the image kernel is
correct can be replaced with some architecture specific data that will allow
the boot kernel to jump to the right address within the image kernel.  These
data should also be used for checking if the image kernel is compatible with
the boot kernel (as far as the memory restroration procedure is concerned).
It can be done, for example, with the help of a "magic" value that has to be
equal in both kernels, so that they can be regarded as compatible.

Signed-off-by: Rafael J. Wysocki <redacted>

ACK.
								Pavel

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