KVM guests freeze under upstream kernel

[Benjamin Herrenschmidt]

On Wed, 2017-07-19 at 16:46 -0300, joserz at linux.vnet.ibm.com wrote:
> Hello!
> 
> We're not able to boot any KVM guest using upstream kernel (cb8c65ccff7f77d0285f1b126c72d37b2572c865 - 4.13.0-rc1+).
> After reaching the SLOF initial counting, the guest simply freezes:

Can you send our .config ?

> SLOF
> **********************************************************************
> QEMU Starting
>  Build Date = Mar  3 2017 13:29:19
>   FW Version = git-66d250ef0fd06bb8
>    Press "s" to enter Open Firmware.
> 
>    C0360
> 
> After bisecting I found the commit:
> 
> https://github.com/torvalds/linux/commit/ebd3119
> 
>     powerpc/mm: Add devmap support for ppc64
> 
>     Add support for the devmap bit on PTEs and PMDs for PPC64 Book3S.  This
>     is used to differentiate device backed memory from transparent huge
>     pages since they are handled in more or less the same manner by the core
>     mm code.
> 
> Reverting the commit and rebuilding 4.13.0-rc1+ was enough to make a workaround.
> But I'll need some help from you guys in order to solve it.
> 
> Thanks!
> 
> Jose Ziviani