Re: [Qemu-devel] KVM-PR is broken with current QEMU

[Thomas Huth <thuth@redhat.com>]

On Wed, 21 Sep 2016 07:45:35 +1000
Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:

> On Tue, 2016-09-20 at 13:44 +0200, Thomas Huth wrote:
> > 
> > Seems like KVM PR is using the "degraded" ISA variants (without the
> > 1TB
> > segments), but the new POWERPC_MMU_64K flag has not been added to
> > those.
> > Has this been done on purpose, or was this just by accident?
> > I can make KVM PR working again with the following patch:
> > 
> > diff --git a/target-ppc/cpu-qom.h b/target-ppc/cpu-qom.h
> > index 2864105..36694cb 100644
> > --- a/target-ppc/cpu-qom.h
> > +++ b/target-ppc/cpu-qom.h
> > @@ -81,6 +81,7 @@ enum powerpc_mmu_t {
> >                               | POWERPC_MMU_AMR | 0x00000003,
> >      /* Architecture 2.06 "degraded" (no 1T segments)           */
> >      POWERPC_MMU_2_06a      = POWERPC_MMU_64 | POWERPC_MMU_AMR
> > +                             | POWERPC_MMU_64K
> >                               | 0x00000003,
> >      /* Architecture 2.07 variant                               */
> >      POWERPC_MMU_2_07       = POWERPC_MMU_64 | POWERPC_MMU_1TSEG
> > @@ -88,6 +89,7 @@ enum powerpc_mmu_t {
> >                               | POWERPC_MMU_AMR | 0x00000004,
> >      /* Architecture 2.07 "degraded" (no 1T segments)           */
> >      POWERPC_MMU_2_07a      = POWERPC_MMU_64 | POWERPC_MMU_AMR
> > +                             | POWERPC_MMU_64K
> >                               | 0x00000004,
> >  };
> > 
> > However, not sure whether this is the right fix ... Cédric, Ben, any
> > ideas?
> 
> Oh I thought I had removed the degraded variants ... Definitely looks
> like an accident. I *think* PR KVM supports 64K pages, no ? If not,
> then we shouldn't enable the flag.. somebody needs to check the kernel.

Yes, it supports 64k pages - but only on POWER8, not on POWER8E or
POWER8NVL yet. I've posted a patch to fix this here:

https://patchwork.ozlabs.org/patch/672841/

 Thomas