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

[David Gibson]

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.

> +        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.

-- 
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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