joserz@linux.vnet.ibm.com writes:

On Thu, Jul 20, 2017 at 10:18:18PM -0300, joserz@linux.vnet.ibm.com wrote:

quoted

On Thu, Jul 20, 2017 at 03:21:59PM +1000, Paul Mackerras wrote:

quoted

Did you check the host kernel logs for any oops messages?

dmesg was clean but after sometime waiting (I forgot QEMU running in
another terminal) I got the oops below (after rebooting the host I 
couldn't reproduce it again).

Another test that I did was:
Compile with transparent huge pages disabled: KVM works fine
Compile with transparent huge pages enabled: doesn't work
  + disabling it in /sys/kernel/mm/transparent_hugepage: doesn't work

Just out of my own curiosity I made this small change:

diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h

b/arch/powerpc/include
index c0737c8..f94a3b6 100644

--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h

@@ -80,7 +80,7 @@
 
  #define _PAGE_SOFT_DIRTY       _RPAGE_SW3 /* software: software dirty
  tracking 
   #define _PAGE_SPECIAL          _RPAGE_SW2 /* software: special page */
   -#define _PAGE_DEVMAP           _RPAGE_SW1 /* software: ZONE_DEVICE page */
   +#define _PAGE_DEVMAP           _RPAGE_RSV3
    #define __HAVE_ARCH_PTE_DEVMAP

and it works. I chose _RPAGE_RSV3 because it uses the same value that
x86 uses (0x0400000000000000UL) but I don't if it could have any side
effect

Does this change make any sense to you people?

No :)

I think it's just hiding the bug somehow. Presumably we have some code
somewhere that is getting confused by _RPAGE_SW1 being set, or setting
that bit incorrectly.

cheers