[PATCH v5 15/15] arm64: hibernate: Prevent resume from a different kernel version

[Chen, Yu C]

> -----Original Message-----
> From: James Morse [mailto:james.morse at arm.com]
> Sent: Thursday, February 18, 2016 8:00 PM
> To: Chen, Yu C
> Cc: Pavel Machek; linux-arm-kernel at lists.infradead.org; Will Deacon; Sudeep
> Holla; Geoff Levand; Catalin Marinas; Lorenzo Pieralisi; Mark Rutland; AKASHI
> Takahiro; Marc Zyngier; Rafael J . Wysocki; linux-pm at vger.kernel.org
> Subject: Re: [PATCH v5 15/15] arm64: hibernate: Prevent resume from a
> different kernel version
> 
> On 17/02/16 02:20, Chen, Yu C wrote:
> >> On Tue 2016-02-16 15:49:27, James Morse wrote:
> > This reminds me a similar problem I once encountered on x86 : - ) The
> > efi memory layout should be strictly the same before/after hibernation,
> right?
> 
> The kernel hopes it is the same, as the page-tables it uses for runtime
> services calls are restored along with the rest of memory, but there is the risk
> that these don't match the EFI memory map any more.
> 
> Even if the amount of memory is the same, the layout might be different.
> (Core hibernate code already has a counter of the number of physical pages.)
I've encountered this situation before.
> 
> I'm still digging through the efi code (and spec), but it is fairly easy to cause
> the memory map to change before entry to linux. This doesn't seem to be a
> problem, as linux happily overwrites most of the allocated areas, so it may
> not be as fragile as I thought.
If I did some peripherals plug/unplug after suspend to hibernation,
then the next time it boots up there would likely be a slightly different efi memory map.
The efi provides a callback of get_memory_map to Linux for retrieving the initial map,
which depends on the bios/bootloader probing/enumeration IMO. The difference of efi
map might lead to kernel panic during resume sometimes.

thanks,
yu