Re: transparent huge pages breaks KVM on AMD.

["Kirill A. Shutemov" <kirill@shutemov.name>]

On Thu, May 12, 2016 at 10:20:09PM +0200, Marc Haber wrote:
> Hi David,
> 
> On Sat, Apr 23, 2016 at 07:52:46PM +0100, Dr. David Alan Gilbert wrote:
> > Hmm, your problem does sound like bad hardware, but....
> > If you've got a nice reliable crash, can you try turning transparent huge pages
> > off on the host;
> >    echo never > /sys/kernel/mm/transparent_hugepage/enabled
> 
> I must have missed this hint in the middle of the "your hardware is
> bad" avalance that came over me.
> 
> I spent two weeks bisecting "good" kernels since during the repeated
> reconfigurations, transparent huge pages got turned off in kernel
> configuration. After running each kernel for 24 hours, I eventually
> ended up with a working 4.5 kernel. The configuration diff was short,
> showing transparent huge pages, and - finally - upon re-reading the
> thread I found your hint.
> 
> I have now the result that 4.5, 4.5.1 and 4.5.4 corrupt KVM guest
> memory reliably in the first hour of running under disk load, causing
> the VM to either drop dead in the water, or to read randomness from
> disk. Rebooting fixes the VM. This happens as soon as transparent huge
> pages are turned on in the host.
> 
> Turning off transparent huge pages by echo never >
> /sys/kernel/mm/transparent_hugepage/enabled fixes the issue even
> without rebooting the host. Start up the VM again and it works just
> fine.
> 
> Is this an issue in (a) transparent huge pages, (b) KVM or (c) qemu?
> Where should this issue be forwarded? Or do we just accept it and turn
> transparent huge pages off?

Could you test this:

http://lkml.kernel.org/r/1463070742-18401-1-git-send-email-aarcange@redhat.com

?

-- 
 Kirill A. Shutemov