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Re: [RFC PATCH-for-8.0 2/3] hw/ppc/spapr: Replace tswap64(HPTE) by cpu_t

From: Peter Maydell
Subject: Re: [RFC PATCH-for-8.0 2/3] hw/ppc/spapr: Replace tswap64(HPTE) by cpu_to_be64(HPTE)
Date: Wed, 21 Dec 2022 22:15:28 +0000

On Wed, 21 Dec 2022 at 16:03, Cédric Le Goater <clg@kaod.org> wrote:
> On 12/21/22 13:33, Peter Maydell wrote:
> > On Wed, 21 Dec 2022 at 01:35, David Gibson <david@gibson.dropbear.id.au> 
> > wrote:
> >> On Mon, Dec 19, 2022 at 10:39:40AM +0000, Peter Maydell wrote:
> >>> OK. I still think we should consistently change all the places that are
> >>> accessing this data structure, though, not just half of them.
> >>
> >> Yes, that makes sense.  Although what exactly constitutes "this data
> >> structure" is a bit complex here.  If we mean just the spapr specific
> >> "external HPT", then there are only a few more references to it.  If
> >> we mean all instances of a powerpc hashed page table, then there are a
> >> bunch more in the cpu target code.
> >
> > I had in mind "places where we write this specific array of bytes
> > spapr->htab".
> spapr_store_hpte() seems to be the most annoying part. It is used
> by hcalls h_enter, h_remove, h_protect. Reworking the interface
> to present pte0/pte1 as BE variables means reworking the whole
> hw/ppc/spapr_softmmu.c file. That's feasible but not a small task
> since the changes will root down in the target hash mmu code which
> is shared by all platforms ... :/

Don't you just need to change spapr_store_hpte() to use stq_be_p()
instead of stq_p() ?

> spapr_hpte_set_c() are spapr_hpte_set_r() are of a different kind.

That code seems to suggest we already implicitly assume that
spapr->htab fields have a given endianness...

-- PMM

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