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

[Erlon Cruz]

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.

> 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?

>
> --
> 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