The ACPI specification says that OSPM should refuse to restore from
hibernate if the hardware signature changes, and should boot from
scratch. However, real BIOSes often vary the hardware signature in cases
where we *do* want to resume from hibernate, so Linux doesn't follow the
spec by default.
However, in a virtual environment there's no reason for the VMM to vary
the hardware signature *unless* it wants to trigger a clean reboot as
defined by the ACPI spec. So enable the check by default if a hypervisor
is detected.
Signed-off-by: David Woodhouse <email address hidden>
Signed-off-by: Rafael J. Wysocki <email address hidden>
(cherry picked from commit f6c46b1d62f8ffbf2cf6eb43ab0d277bd3f7e948 linux-next)
Signed-off-by: Tim Gardner <email address hidden>
Acked-by: Stefan Bader <email address hidden>
Acked-by: Ian May <email address hidden>
Signed-off-by: Tim Gardner <email address hidden>
3184be0...
by
David Woodhouse <email address hidden>
PM: hibernate: Allow ACPI hardware signature to be honoured
Theoretically, when the hardware signature in FACS changes, the OS
is supposed to gracefully decline to attempt to resume from S4:
"If the signature has changed, OSPM will not restore the system
context and can boot from scratch"
In practice, Windows doesn't do this and many laptop vendors do allow
the signature to change especially when docking/undocking, so it would
be a bad idea to simply comply with the specification by default in the
general case.
However, there are use cases where we do want the compliant behaviour
and we know it's safe. Specifically, when resuming virtual machines where
we know the hypervisor has changed sufficiently that resume will fail.
We really want to be able to *tell* the guest kernel not to try, so it
boots cleanly and doesn't just crash. This patch provides a way to opt
in to the spec-compliant behaviour on the command line.
A follow-up patch may do this automatically for certain "known good"
machines based on a DMI match, or perhaps just for all hypervisor
guests since there's no good reason a hypervisor would change the
hardware_signature that it exposes to guests *unless* it wants them
to obey the ACPI specification.
Signed-off-by: David Woodhouse <email address hidden>
Signed-off-by: Rafael J. Wysocki <email address hidden>
(cherry picked from commit 74d9555580c48a04b2c3b742dfb0c80777aa0b26)
Signed-off-by: Tim Gardner <email address hidden>
Acked-by: Stefan Bader <email address hidden>
Acked-by: Ian May <email address hidden>
Signed-off-by: Tim Gardner <email address hidden>
