Re: [Qemu-devel] [RFC for-2.13 1/7] spapr: Maximum (HPT) pagesize property

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, May 02, 2018 at 06:06:38PM -0300, Murilo Opsfelder Araujo wrote:
> On Thu, Apr 19, 2018 at 04:29:11PM +1000, David Gibson wrote:
> > The way the POWER Hash Page Table (HPT) MMU is virtualized by KVM HV means
> > that every page that the guest puts in the pagetables must be truly
> > physically contiguous, not just GPA-contiguous.  In effect this means that
> > an HPT guest can't use any pagesizes greater than the host page size used
> > to back its memory.
> > 
> > At present we handle this by changing what we advertise to the guest based
> > on the backing pagesizes.  This is pretty bad, because it means the guest
> > sees a different environment depending on what should be host configuration
> > details.
> > 
> > As a start on fixing this, we add a new capability parameter to the pseries
> > machine type which gives the maximum allowed pagesizes for an HPT guest (as
> > a shift).  For now we just create and validate the parameter without making
> > it do anything.
> > 
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> >  hw/ppc/spapr.c         |  1 +
> >  hw/ppc/spapr_caps.c    | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++
> >  include/hw/ppc/spapr.h |  4 +++-
> >  3 files changed, 57 insertions(+), 1 deletion(-)
> > 
> > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > index bdf72e1e89..36e41aff71 100644
> > --- a/hw/ppc/spapr.c
> > +++ b/hw/ppc/spapr.c
> > @@ -3876,6 +3876,7 @@ static void spapr_machine_class_init(ObjectClass *oc, void *data)
> >      smc->default_caps.caps[SPAPR_CAP_CFPC] = SPAPR_CAP_BROKEN;
> >      smc->default_caps.caps[SPAPR_CAP_SBBC] = SPAPR_CAP_BROKEN;
> >      smc->default_caps.caps[SPAPR_CAP_IBS] = SPAPR_CAP_BROKEN;
> > +    smc->default_caps.caps[SPAPR_CAP_HPT_MPS] = 16; /* Allow 64kiB pages */
> >      spapr_caps_add_properties(smc, &error_abort);
> >  }
> >  
> > diff --git a/hw/ppc/spapr_caps.c b/hw/ppc/spapr_caps.c
> > index 531e145114..cbc41f5b20 100644
> > --- a/hw/ppc/spapr_caps.c
> > +++ b/hw/ppc/spapr_caps.c
> > @@ -27,6 +27,7 @@
> >  #include "qapi/visitor.h"
> >  #include "sysemu/hw_accel.h"
> >  #include "target/ppc/cpu.h"
> > +#include "target/ppc/mmu-hash64.h"
> >  #include "cpu-models.h"
> >  #include "kvm_ppc.h"
> >  
> > @@ -142,6 +143,39 @@ out:
> >      g_free(val);
> >  }
> >  
> > +static void spapr_cap_get_int(Object *obj, Visitor *v, const char *name,
> > +                               void *opaque, Error **errp)
> > +{
> > +    sPAPRCapabilityInfo *cap = opaque;
> > +    sPAPRMachineState *spapr = SPAPR_MACHINE(obj);
> > +    int64_t value = spapr_get_cap(spapr, cap->index);
> > +
> > +    visit_type_int(v, name, &value, errp);
> > +}
> > +
> > +static void spapr_cap_set_int(Object *obj, Visitor *v, const char *name,
> > +                               void *opaque, Error **errp)
> > +{
> > +    sPAPRCapabilityInfo *cap = opaque;
> > +    sPAPRMachineState *spapr = SPAPR_MACHINE(obj);
> > +    int64_t value;
> > +    Error *local_err = NULL;
> > +
> > +    visit_type_int(v, name, &value, &local_err);
> > +    if (local_err) {
> > +        error_propagate(errp, local_err);
> > +        return;
> > +    }
> > +
> > +    if ((value < 0) || (value > 255)) {
> > +        error_setg(errp, "Value for %s out of range (0..255)", name);
> > +        return;
> > +    }
> > +
> > +    spapr->cmd_line_caps[cap->index] = true;
> > +    spapr->eff.caps[cap->index] = value;
> > +}
> > +
> 
> Hi, David.
> 
> Do you think uint8_t would fit better for spapr_[gs]et_int() functions?
> 
> Perhaps renaming them to spapr_[gs]set_int8() and calling
> visit_type_int8() instead.

Yeah, that's a good idea.  Using visit_type_uint8 means we don't need
to implement our own clamping.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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