KASLR causes intermittent boot failures on some systems

Dave Young dyoung at redhat.com
Wed Apr 12 01:24:33 PDT 2017

On 04/07/17 at 10:41am, Jeff Moyer wrote:
> Hi,
> commit 021182e52fe01 ("x86/mm: Enable KASLR for physical mapping memory
> regions") causes some of my systems with persistent memory (whether real
> or emulated) to fail to boot with a couple of different crash
> signatures.  The first signature is a NMI watchdog lockup of all but 1
> cpu, which causes much difficulty in extracting useful information from
> the console.  The second variant is an invalid paging request, listed
> below.
> On some systems, I haven't hit this problem at all.  Other systems
> experience a failed boot maybe 20-30% of the time.  To reproduce it,
> configure some emulated pmem on your system.  You can find directions
> for that here: https://nvdimm.wiki.kernel.org/
> Install ndctl (https://github.com/pmem/ndctl).
> Configure the namespace:
> # ndctl create-namespace -f -e namespace0.0 -m memory
> Then just reboot several times (5 should be enough), and hopefully
> you'll hit the issue.
> I've attached both my .config and the dmesg output from a successful
> boot at the end of this mail.

I did some tests about emulated pmem via memmap=, kdump kernel hangs or
just reboots early during compressing kernel, no clue how to handle it.
Since for kdump kernel kaslr is pointless a workaround is use "nokaslr"

In Fedora or RHEL, just add "nokaslr" in KDUMP_COMMANDLINE_APPEND
in /etc/sysconfig/kdump 

Can you try if this works?


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