KASLR causes intermittent boot failures on some systems

[Dave Young]

On 04/12/17 at 04:24pm, Dave Young wrote:
> 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.
> > 
> [snip]
> 
> 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.

s/compressing/uncompressing

> 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?
> 
> Thanks
> Dave