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

Anshuman Khandual
2022-02-22T05:44:46Z

On 2/21/22 5:24 PM, Geert Uytterhoeven wrote:
> 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?

Sure, will move (#ifdef CONFIG_COLDFIRE will not be required anymore).

>
>> +{
>> + 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?

IMHO, it is worth preserving the existing switch case sequence as vm_flags
moves linearly from VM_NONE to (VM_SHARED|VM_EXEC|VM_WRITE|VM_READ). This
proposal did not attempt to further optimize any common page prot values
for various vm_flags combinations even on other platforms.

>
>> + 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?

Sure, will move (#ifdef CONFIG_SUN3 will not be required anymore).

>
>> +{
>> + 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...

Only when they follow vm_flags linear sequence.

>
>> + return PAGE_COPY;
>> + case VM_EXEC:
>> + case VM_EXEC | VM_READ:
>> + return PAGE_READONLY;
>
> But not all? More below...

Right, because did not want to shuffle up vm_flags linear sequence.

>
>> + 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:

Right.

>
> #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)

Will drop all _C definitions and change switch case as mentioned above.

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

Right, will remove them all.

>
>> +
>> + 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...

As explained earlier.