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

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Message-ID: <0b00a30e-cb7f-d42b-7d16-0ae8d50ed916@gmail.com>
Date:   Mon, 6 Mar 2023 09:44:17 +1300
From:   Michael Schmitz <schmitzmic@...il.com>
To:     Matthew Wilcox <willy@...radead.org>,
        Geert Uytterhoeven <geert@...ux-m68k.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 Matthew, Geert,

sorry, I missed that one when it got posted ...

On 6/03/23 04:28, Matthew Wilcox 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;".

Are we certain that contiguous vaddr always maps to contiguous paddr?

If not, I'd suggest we increment vaddr inside the loop, and use __pa() 
each time:

> +++ 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) {
>   
> -               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" __pa(vaddr));
> +                       vaddr += PAGE_SIZE;
> +               } while (--nr);
>          } else {
>                  unsigned long _tmp;
>                  __asm__ __volatile__("movec %%cacr,%0\n\t"
>
(just edited Matthew's patch in the mail editor, untested, may not apply 
cleanly ...)

Cheers,

     Michael