Re: [PATCH V2 08/30] m68k/mm: Enable ARCH_HAS_VM_GET_PAGE_PROT

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Anshuman,

On Mon, Feb 21, 2022 at 9:45 AM Anshuman Khandual
<anshuman.khandual@arm.com> wrote:
> This defines and exports a platform specific custom vm_get_page_prot() via
> subscribing ARCH_HAS_VM_GET_PAGE_PROT. Subsequently all __SXXX and __PXXX
> macros can be dropped which are no longer needed.
>
> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
> Cc: linux-m68k@lists.linux-m68k.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>

Thanks for your patch!

> --- a/arch/m68k/mm/init.c
> +++ b/arch/m68k/mm/init.c
> @@ -128,3 +128,107 @@ void __init mem_init(void)
>         memblock_free_all();
>         init_pointer_tables();
>  }
> +
> +#ifdef CONFIG_COLDFIRE
> +/*
> + * Page protections for initialising protection_map. See mm/mmap.c
> + * for use. In general, the bit positions are xwr, and P-items are
> + * private, the S-items are shared.
> + */
> +pgprot_t vm_get_page_prot(unsigned long vm_flags)

Wouldn't it make more sense to add this to arch/m68k/mm/mcfmmu.c?

> +{
> +       switch (vm_flags & (VM_READ | VM_WRITE | VM_EXEC | VM_SHARED)) {
> +       case VM_NONE:
> +               return PAGE_NONE;
> +       case VM_READ:
> +               return __pgprot(CF_PAGE_VALID | CF_PAGE_ACCESSED |
> +                               CF_PAGE_READABLE);
> +       case VM_WRITE:
> +               return __pgprot(CF_PAGE_VALID | CF_PAGE_ACCESSED |
> +                               CF_PAGE_WRITABLE);
> +       case VM_WRITE | VM_READ:
> +               return __pgprot(CF_PAGE_VALID | CF_PAGE_ACCESSED |
> +                               CF_PAGE_READABLE | CF_PAGE_WRITABLE);
> +       case VM_EXEC:
> +               return __pgprot(CF_PAGE_VALID | CF_PAGE_ACCESSED |
> +                               CF_PAGE_EXEC);
> +       case VM_EXEC | VM_READ:
> +               return __pgprot(CF_PAGE_VALID | CF_PAGE_ACCESSED |
> +                               CF_PAGE_READABLE | CF_PAGE_EXEC);
> +       case VM_EXEC | VM_WRITE:
> +               return __pgprot(CF_PAGE_VALID | CF_PAGE_ACCESSED |
> +                               CF_PAGE_WRITABLE | CF_PAGE_EXEC);
> +       case VM_EXEC | VM_WRITE | VM_READ:
> +               return __pgprot(CF_PAGE_VALID | CF_PAGE_ACCESSED |
> +                               CF_PAGE_READABLE | CF_PAGE_WRITABLE |
> +                               CF_PAGE_EXEC);
> +       case VM_SHARED:
> +               return PAGE_NONE;
> +       case VM_SHARED | VM_READ:
> +               return __pgprot(CF_PAGE_VALID | CF_PAGE_ACCESSED |
> +                               CF_PAGE_READABLE);

This is the same as the plain VM_READ case.
Perhaps they can be merged?

> +       case VM_SHARED | VM_WRITE:
> +               return PAGE_SHARED;
> +       case VM_SHARED | VM_WRITE | VM_READ:
> +               return __pgprot(CF_PAGE_VALID | CF_PAGE_ACCESSED |
> +                               CF_PAGE_READABLE | CF_PAGE_SHARED);
> +       case VM_SHARED | VM_EXEC:
> +               return __pgprot(CF_PAGE_VALID | CF_PAGE_ACCESSED |
> +                               CF_PAGE_EXEC);

Same as plain VM_EXEC.

> +       case VM_SHARED | VM_EXEC | VM_READ:
> +               return __pgprot(CF_PAGE_VALID | CF_PAGE_ACCESSED |
> +                               CF_PAGE_READABLE | CF_PAGE_EXEC);

Same as plain VM_EXEC | VM_READ.

> +       case VM_SHARED | VM_EXEC | VM_WRITE:
> +               return __pgprot(CF_PAGE_VALID | CF_PAGE_ACCESSED |
> +                               CF_PAGE_SHARED | CF_PAGE_EXEC);
> +       case VM_SHARED | VM_EXEC | VM_WRITE | VM_READ:
> +               return __pgprot(CF_PAGE_VALID | CF_PAGE_ACCESSED |
> +                               CF_PAGE_READABLE | CF_PAGE_SHARED |
> +                               CF_PAGE_EXEC);
> +       default:
> +               BUILD_BUG();
> +       }
> +}
> +#endif
> +
> +#ifdef CONFIG_SUN3
> +/*
> + * Page protections for initialising protection_map. The sun3 has only two
> + * protection settings, valid (implying read and execute) and writeable. These
> + * are as close as we can get...
> + */
> +pgprot_t vm_get_page_prot(unsigned long vm_flags)

Wouldn't it make more sense to add this to arch/m68k/mm/sun3mmu.c?

> +{
> +       switch (vm_flags & (VM_READ | VM_WRITE | VM_EXEC | VM_SHARED)) {
> +       case VM_NONE:
> +               return PAGE_NONE;
> +       case VM_READ:
> +               return PAGE_READONLY;
> +       case VM_WRITE:
> +       case VM_WRITE | VM_READ:

So you did merge some of them...

> +               return PAGE_COPY;
> +       case VM_EXEC:
> +       case VM_EXEC | VM_READ:
> +               return PAGE_READONLY;

But not all? More below...

> +       case VM_EXEC | VM_WRITE:
> +       case VM_EXEC | VM_WRITE | VM_READ:
> +               return PAGE_COPY;
> +       case VM_SHARED:
> +               return PAGE_NONE;
> +       case VM_SHARED | VM_READ:
> +               return PAGE_READONLY;
> +       case VM_SHARED | VM_WRITE:
> +       case VM_SHARED | VM_WRITE | VM_READ:
> +               return PAGE_SHARED;
> +       case VM_SHARED | VM_EXEC:
> +       case VM_SHARED | VM_EXEC | VM_READ:
> +               return PAGE_READONLY;
> +       case VM_SHARED | VM_EXEC | VM_WRITE:
> +       case VM_SHARED | VM_EXEC | VM_WRITE | VM_READ:
> +               return PAGE_SHARED;
> +       default:
> +               BUILD_BUG();
> +       }
> +}
> +#endif
> +EXPORT_SYMBOL(vm_get_page_prot);
> diff --git a/arch/m68k/mm/motorola.c b/arch/m68k/mm/motorola.c
> index ecbe948f4c1a..495ba0ea083c 100644
> --- a/arch/m68k/mm/motorola.c
> +++ b/arch/m68k/mm/motorola.c
> @@ -400,12 +400,9 @@ void __init paging_init(void)
>
>         /* Fix the cache mode in the page descriptors for the 680[46]0.  */
>         if (CPU_IS_040_OR_060) {
> -               int i;
>  #ifndef mm_cachebits
>                 mm_cachebits = _PAGE_CACHE040;
>  #endif
> -               for (i = 0; i < 16; i++)
> -                       pgprot_val(protection_map[i]) |= _PAGE_CACHE040;
>         }
>
>         min_addr = m68k_memory[0].addr;
> @@ -483,3 +480,48 @@ void __init paging_init(void)
>         max_zone_pfn[ZONE_DMA] = memblock_end_of_DRAM();
>         free_area_init(max_zone_pfn);
>  }
> +
> +/*
> + * The m68k can't do page protection for execute, and considers that
> + * the same are read. Also, write permissions imply read permissions.
> + * This is the closest we can get..
> + */
> +pgprot_t vm_get_page_prot(unsigned long vm_flags)

Good, this one is in arch/m68k/mm/motorola.c :-)

> +{
> +       unsigned long cachebits = 0;
> +
> +       if (CPU_IS_040_OR_060)
> +               cachebits = _PAGE_CACHE040;

If you would use the non-"_C"-variants (e.g. PAGE_NONE instead of
PAGE_NONE_C) below, you would get the cachebits handling for free!
After that, the "_C" variants are no longer used, and can be removed.
Cfr. arch/m68k/include/asm/motorola_pgtable.h:

    #define PAGE_NONE       __pgprot(_PAGE_PROTNONE | _PAGE_ACCESSED |
mm_cachebits)
    #define PAGE_SHARED     __pgprot(_PAGE_PRESENT | _PAGE_ACCESSED |
mm_cachebits)
    #define PAGE_COPY       __pgprot(_PAGE_PRESENT | _PAGE_RONLY |
_PAGE_ACCESSED | mm_cachebits)
    #define PAGE_READONLY   __pgprot(_PAGE_PRESENT | _PAGE_RONLY |
_PAGE_ACCESSED | mm_cachebits)
    #define PAGE_KERNEL     __pgprot(_PAGE_PRESENT | _PAGE_DIRTY |
_PAGE_ACCESSED | mm_cachebits)

    /* Alternate definitions that are compile time constants, for
       initializing protection_map.  The cachebits are fixed later.  */
    #define PAGE_NONE_C     __pgprot(_PAGE_PROTNONE | _PAGE_ACCESSED)
    #define PAGE_SHARED_C   __pgprot(_PAGE_PRESENT | _PAGE_ACCESSED)
    #define PAGE_COPY_C     __pgprot(_PAGE_PRESENT | _PAGE_RONLY |
_PAGE_ACCESSED)
    #define PAGE_READONLY_C __pgprot(_PAGE_PRESENT | _PAGE_RONLY |
_PAGE_ACCESSED)

BTW, this shows you left a reference in a comment to the now-gone
"protection_map".  There are several more across the tree.

> +
> +       switch (vm_flags & (VM_READ | VM_WRITE | VM_EXEC | VM_SHARED)) {
> +       case VM_NONE:
> +               return __pgprot(pgprot_val(PAGE_NONE_C) | cachebits);
> +       case VM_READ:
> +               return __pgprot(pgprot_val(PAGE_READONLY_C) | cachebits);
> +       case VM_WRITE:
> +       case VM_WRITE | VM_READ:
> +               return __pgprot(pgprot_val(PAGE_COPY_C) | cachebits);
> +       case VM_EXEC:
> +       case VM_EXEC | VM_READ:
> +               return __pgprot(pgprot_val(PAGE_READONLY_C) | cachebits);
> +       case VM_EXEC | VM_WRITE:
> +       case VM_EXEC | VM_WRITE | VM_READ:
> +               return __pgprot(pgprot_val(PAGE_COPY_C) | cachebits);
> +       case VM_SHARED:
> +               return __pgprot(pgprot_val(PAGE_NONE_C) | cachebits);

Same as the VM_NONE case.  More to be merged below...

> +       case VM_SHARED | VM_READ:
> +               return __pgprot(pgprot_val(PAGE_READONLY_C) | cachebits);
> +       case VM_SHARED | VM_WRITE:
> +       case VM_SHARED | VM_WRITE | VM_READ:
> +               return __pgprot(pgprot_val(PAGE_SHARED_C) | cachebits);
> +       case VM_SHARED | VM_EXEC:
> +       case VM_SHARED | VM_EXEC | VM_READ:
> +               return __pgprot(pgprot_val(PAGE_READONLY_C) | cachebits);
> +       case VM_SHARED | VM_EXEC | VM_WRITE:
> +       case VM_SHARED | VM_EXEC | VM_WRITE | VM_READ:
> +               return __pgprot(pgprot_val(PAGE_SHARED_C) | cachebits);
> +       default:
> +               BUILD_BUG();
> +       }
> +}
> +EXPORT_SYMBOL(vm_get_page_prot);

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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