linux-kernel - Re: [PATCH v3 13/34] m68k: Implement the new page table range API

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Date:   Sun, 5 Mar 2023 17:48:51 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-mm@...ck.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-m68k@...ts.linux-m68k.org
Subject: Re: [PATCH v3 13/34] m68k: Implement the new page table range API

Hi Willy,

On Sun, Mar 5, 2023 at 4:28 PM Matthew Wilcox <willy@...radead.org> wrote:
> On Sun, Mar 05, 2023 at 11:16:13AM +0100, Geert Uytterhoeven wrote:
> > > +               while (nr--) {
> > > +                       __asm__ __volatile__("nop\n\t"
> > > +                                            ".chip 68040\n\t"
> > > +                                            "cpushp %%bc,(%0)\n\t"
> > > +                                            ".chip 68k"
> > > +                                            : : "a" (paddr + nr * PAGE_SIZE));
> >
> > As gcc (9.5.0) keeps on calculating "paddr + nr * PAGE_SIZE"
> > inside the loop (albeit using a shift instead of a multiplication),
> > please use "paddr" here, followed by "paddr += PAGE_SIZE;".
>
> Thanks.  So this?
>
> +++ b/arch/m68k/include/asm/cacheflush_mm.h
> @@ -235,13 +235,14 @@ static inline void __flush_pages_to_ram(void *vaddr, unsigned int nr)
>         } else if (CPU_IS_040_OR_060) {
>                 unsigned long paddr = __pa(vaddr);
>
> -               while (nr--) {
> +               do {
>                         __asm__ __volatile__("nop\n\t"
>                                              ".chip 68040\n\t"
>                                              "cpushp %%bc,(%0)\n\t"
>                                              ".chip 68k"
> -                                            : : "a" (paddr + nr * PAGE_SIZE));
> -               }
> +                                            : : "a" (paddr));
> +                       paddr += PAGE_SIZE;
> +               } while (--nr);
>         } else {
>                 unsigned long _tmp;
>                 __asm__ __volatile__("movec %%cacr,%0\n\t"

LGTM. Might be safer to keep the "while (nr--) {", just in case someone
ever passes zero.

> Also, I noticed that I broke sun3.  It puts the PFN in bits 0-n instead
> of 12-n.  New patch coming soon.

Thanks, hadn't noticed (there are no sun3-specific code changes in
this series?)

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds