Re: [Resend][PATCH] x86/power/64: Always create temporary identity mapping correctly

On Thu, Aug 11, 2016 at 3:17 AM, Thomas Garnier [off-list ref] wrote:

On Wed, Aug 10, 2016 at 5:35 PM, Rafael J. Wysocki [off-list ref] wrote:

quoted

On Wed, Aug 10, 2016 at 11:59 PM, Jiri Kosina [off-list ref] wrote:

quoted

On Wed, 10 Aug 2016, Rafael J. Wysocki wrote:

quoted

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
CONFIG_PROVE_LOCKING and CONFIG_DEBUG_LOCK_ALLOC (which also will
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!

quoted

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:
http://git.kernel.org/cgit/linux/kernel/git/tip/tip.git/commit/?id=fb754f958f8e46202c1efd7f66d5b3db1208117d

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.

Thanks,
Rafael