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Date: Thu, 11 Aug 2016 03:35:39 +0200
From: "Rafael J. Wysocki" <>
To: Thomas Garnier <>
Cc: "Rafael J. Wysocki" <>, Jiri Kosina <>, Borislav Petkov <>, 
	"Rafael J. Wysocki" <>, Linux PM list <>, 
	"the arch/x86 maintainers" <>, Linux Kernel Mailing List <>, 
	Yinghai Lu <>, Thomas Gleixner <>, Ingo Molnar <>, 
	"H . Peter Anvin" <>, Kees Cook <>, Pavel Machek <>, 
	Kernel Hardening <>
Subject: Re: [Resend][PATCH] x86/power/64: Always create temporary identity
 mapping correctly

On Thu, Aug 11, 2016 at 3:17 AM, Thomas Garnier <> wrote:
> On Wed, Aug 10, 2016 at 5:35 PM, Rafael J. Wysocki <> wrote:
>> On Wed, Aug 10, 2016 at 11:59 PM, Jiri Kosina <> wrote:
>>> On Wed, 10 Aug 2016, Rafael J. Wysocki wrote:
>>>> So I used your .config to generate one for my test machine and with
>>>> that I can reproduce.
>>> Was that the config I've sent, or did Boris provide one as well? Which one
>>> are you able to reproduce with please?
>> It's the Boris' one.
>> Moreover, I have found the options that make the difference: unsetting
>> unset CONFIG_LOCKDEP AFAICS) in it makes hibernation work again with
>> CONFIG_RANDOMIZE_MEMORY set and with the $subject patch applied.
>> Unbelievable, but that's what I'm seeing.
> Nice find!
>> Now, that leads to a few questions:
>> - How does lockdep change the picture so it matters for hibernation?
>> - Why is hibernation the only piece that's affected?
>> - Why is RANDOMIZE_MEMORY necessary to make this breakage show up?
>> Thomas, any ideas?
> No idea so far. I will investigate though.
> We had an unrelated issue with CONFIG_DEBUG_PAGEALLOC on early boot. I
> don't think it was related because it was on early boot and with
> certain e820 memory layout (and PUD randomization that I disabled on
> the previous patch test). The fix is on tip:

Well, I don't think this is related.

In the meantime, I went back to my original .config and verified that
setting CONFIG_DEBUG_LOCK_ALLOC in it caused hibernation to fail (with
CONFIG_RANDOMIZE_MEMORY set and with the $subject patch applied), so
this really matters somehow.

Besides, now that I have a reproducer, I can check various other
things and for example this change (sorry for broken whitespace):

Index: linux-pm/arch/x86/mm/kaslr.c
--- linux-pm.orig/arch/x86/mm/kaslr.c
+++ linux-pm/arch/x86/mm/kaslr.c
@@ -122,7 +122,7 @@ void __init kernel_randomize_memory(void
         prandom_bytes_state(&rand_state, &rand, sizeof(rand));
         entropy = (rand % (entropy + 1)) & PUD_MASK;
         vaddr += entropy;
-        *kaslr_regions[i].base = vaddr;
+        *kaslr_regions[i].base += PUD_SIZE;

          * Jump the region and add a minimum padding based on

makes hibernation work for me again in the above configuration.  To
me, this means that the $subject patch works as expected and the
problem really is related to the vaddr value being too big.


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