Re: [PATCH V4 2/7] powerpc/mm: Enable ARCH_HAS_VM_GET_PAGE_PROT

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 08/04/2022 à 14:53, Christophe Leroy a écrit :
> 
> 
> Le 07/04/2022 à 12:32, Anshuman Khandual a écrit :
>> This defines and exports a platform specific custom vm_get_page_prot() 
>> via
>> subscribing ARCH_HAS_VM_GET_PAGE_PROT. While here, this also localizes
>> arch_vm_get_page_prot() as powerpc_vm_get_page_prot() and moves it near
>> vm_get_page_prot().
>>
>> Cc: Michael Ellerman <mpe@ellerman.id.au>
>> Cc: Paul Mackerras <paulus@samba.org>
>> Cc: linuxppc-dev@lists.ozlabs.org
>> Cc: linux-kernel@vger.kernel.org
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
>> ---
>>   arch/powerpc/Kconfig            |  1 +
>>   arch/powerpc/include/asm/mman.h | 12 ------------
>>   arch/powerpc/mm/mmap.c          | 26 ++++++++++++++++++++++++++
>>   3 files changed, 27 insertions(+), 12 deletions(-)
>>
>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
>> index 174edabb74fa..eb9b6ddbf92f 100644
>> --- a/arch/powerpc/Kconfig
>> +++ b/arch/powerpc/Kconfig
>> @@ -140,6 +140,7 @@ config PPC
>>       select ARCH_HAS_TICK_BROADCAST        if 
>> GENERIC_CLOCKEVENTS_BROADCAST
>>       select ARCH_HAS_UACCESS_FLUSHCACHE
>>       select ARCH_HAS_UBSAN_SANITIZE_ALL
>> +    select ARCH_HAS_VM_GET_PAGE_PROT
>>       select ARCH_HAVE_NMI_SAFE_CMPXCHG
>>       select ARCH_KEEP_MEMBLOCK
>>       select ARCH_MIGHT_HAVE_PC_PARPORT
>> diff --git a/arch/powerpc/include/asm/mman.h 
>> b/arch/powerpc/include/asm/mman.h
>> index 7cb6d18f5cd6..1b024e64c8ec 100644
>> --- a/arch/powerpc/include/asm/mman.h
>> +++ b/arch/powerpc/include/asm/mman.h
>> @@ -24,18 +24,6 @@ static inline unsigned long 
>> arch_calc_vm_prot_bits(unsigned long prot,
>>   }
>>   #define arch_calc_vm_prot_bits(prot, pkey) 
>> arch_calc_vm_prot_bits(prot, pkey)
>> -static inline pgprot_t arch_vm_get_page_prot(unsigned long vm_flags)
>> -{
>> -#ifdef CONFIG_PPC_MEM_KEYS
>> -    return (vm_flags & VM_SAO) ?
>> -        __pgprot(_PAGE_SAO | vmflag_to_pte_pkey_bits(vm_flags)) :
>> -        __pgprot(0 | vmflag_to_pte_pkey_bits(vm_flags));
>> -#else
>> -    return (vm_flags & VM_SAO) ? __pgprot(_PAGE_SAO) : __pgprot(0);
>> -#endif
>> -}
>> -#define arch_vm_get_page_prot(vm_flags) arch_vm_get_page_prot(vm_flags)
>> -
>>   static inline bool arch_validate_prot(unsigned long prot, unsigned 
>> long addr)
>>   {
>>       if (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM | 
>> PROT_SAO))
>> diff --git a/arch/powerpc/mm/mmap.c b/arch/powerpc/mm/mmap.c
>> index c475cf810aa8..cd17bd6fa36b 100644
>> --- a/arch/powerpc/mm/mmap.c
>> +++ b/arch/powerpc/mm/mmap.c
>> @@ -254,3 +254,29 @@ void arch_pick_mmap_layout(struct mm_struct *mm, 
>> struct rlimit *rlim_stack)
>>           mm->get_unmapped_area = arch_get_unmapped_area_topdown;
>>       }
>>   }
>> +
>> +#ifdef CONFIG_PPC64
>> +static pgprot_t powerpc_vm_get_page_prot(unsigned long vm_flags)
>> +{
>> +#ifdef CONFIG_PPC_MEM_KEYS
>> +    return (vm_flags & VM_SAO) ?
>> +        __pgprot(_PAGE_SAO | vmflag_to_pte_pkey_bits(vm_flags)) :
>> +        __pgprot(0 | vmflag_to_pte_pkey_bits(vm_flags));
>> +#else
>> +    return (vm_flags & VM_SAO) ? __pgprot(_PAGE_SAO) : __pgprot(0);
>> +#endif
>> +}
>> +#else
>> +static pgprot_t powerpc_vm_get_page_prot(unsigned long vm_flags)
>> +{
>> +    return __pgprot(0);
>> +}
>> +#endif /* CONFIG_PPC64 */
> 
> Can we reduce this forest of #ifdefs and make it more readable ?
> 
> mm/mmap.c is going away with patch 
> https://patchwork.ozlabs.org/project/linuxppc-dev/patch/d6d849621f821af253e777a24eda4c648814a76e.1646847562.git.christophe.leroy@csgroup.eu/ 
> 
> 
> So it would be better to add two versions of vm_get_page_prot(), for 
> instance one in mm/pgtable_64.c and one in mm/pgtable_32.c

Indeed, you don't need anything at all for PPC32. All you need to do is

	select ARCH_HAS_VM_GET_PAGE_PROT if PPC64

And in fact it could even be PPC_BOOK3S_64 instead of PPC64 because 
CONFIG_PPC_MEM_KEYS depends on PPC_BOOK3S_64 and _PAGE_SAO is 0 on 
nohash/64.

So you can then put it into arch/powerpc/mm/book3s64/pgtable.c


> 
> 
>> +
>> +pgprot_t vm_get_page_prot(unsigned long vm_flags)
>> +{
>> +    return __pgprot(pgprot_val(protection_map[vm_flags &
>> +            (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]) |
>> +           pgprot_val(powerpc_vm_get_page_prot(vm_flags)));
>> +}
>> +EXPORT_SYMBOL(vm_get_page_prot);
> 
> By the way I'm a bit puzzled with the name powerpc_vm_get_page_prot(), 
> the name suggests that it's just a powerpc replacement of 
> vm_get_page_prot(). I'd prefer if it was named __vm_get_page_prot(), it 
> would be clearer that it is a complement to vm_get_page_prot() and not a 
> remplacement.
> 
> Christophe