Re: [Qemu-devel] [Qemu-ppc] [PATCH] pseries: Implements h_read hcall

[David Gibson]

On Thu, Feb 14, 2013 at 10:44:34AM -0200, Erlon Cruz wrote:
> On Sun, Feb 10, 2013 at 10:10 PM, David Gibson
> <address@hidden> wrote:
> >
> > On Thu, Feb 07, 2013 at 09:28:20AM -0200, Erlon Cruz wrote:
> > > From: Erlon Cruz <address@hidden>
> > >
> > > This h_call is useful for DLPAR in future amongst other things. Given an 
> > > index
> > > it fetches the corresponding PTE stored in the htab.
> >
> > Nice.  It would be good to add in this little bit of PAPR compliance.
> >
> > Couple of small nits in the implementation:
> >
> > >
> > > Signed-off-by: Erlon Cruz <address@hidden>
> > > ---
> > >  hw/spapr_hcall.c |   58 
> > > ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > >  1 file changed, 58 insertions(+)
> > >
> > > diff --git a/hw/spapr_hcall.c b/hw/spapr_hcall.c
> > > index 2889742..5ba07e5 100644
> > > --- a/hw/spapr_hcall.c
> > > +++ b/hw/spapr_hcall.c
> > > @@ -323,6 +323,63 @@ static target_ulong h_protect(PowerPCCPU *cpu, 
> > > sPAPREnvironment *spapr,
> > >      return H_SUCCESS;
> > >  }
> > >
> > > +static target_ulong h_read(PowerPCCPU *cpu, sPAPREnvironment *spapr,
> > > +                            target_ulong opcode, target_ulong *args)
> > > +{
> > > +    CPUPPCState *env = &cpu->env;
> > > +    target_ulong flags = args[0];
> > > +    target_ulong pte_index = args[1];
> > > +    uint8_t *hpte;
> > > +
> > > +    if ((pte_index * HASH_PTE_SIZE_64) & ~env->htab_mask) {
> > > +        return H_PARAMETER;
> > > +    }
> > > +
> > > +    if (!(flags & H_READ_4)) {
> >
> > It would be nice to combine the H_READ_4 and !H_READ_4 paths together,
> > since except for the masking and stopping sooner the !H_READ_4 path is
> > just like the H_READ_4 path.
> 
> Ok.
> 
> >
> >
> > > +        target_ulong v, r;
> > > +        target_ulong *pteh = &args[0];
> > > +        target_ulong *ptel = &args[1];
> > > +
> > > +        hpte = env->external_htab + (pte_index * HASH_PTE_SIZE_64);
> > > +
> > > +        v = ldq_p(hpte);
> > > +        r = ldq_p(hpte + (HASH_PTE_SIZE_64/2));
> > > +
> > > +        if (flags & H_R_XLATE) {
> > > +            /* FIXME:  include a valid logical page num in the pte */
> >
> > This comment is misleading.  Since you do copy out both words of the
> > hpte, and qemu stores the external_htab in terms of guest physical (==
> > logical) addresses, in fact you're *always* supplying a valid logical
> > page num.  So you've already correctly implemented the flag as a
> > no-op.
> >
> > I believe that flag is included for the benefit of a true hypervisor,
> > where the native htab would be stored as true physical addresses, and
> > it might be expensive for the hypervisor to recompute the logical
> > address.
> 
> Ok, then I think we can just skip this checking.

Yes.

> > That said, I actually wrote such helpers about 15 minutes ago as part
> > of my MMU cleanup series.
> 
>  Should I wait for the helpers to send It again?

Probably not, my series will be a little while because it will
probably need to wait for the big cpu qomification series.

-- 
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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