Subject: Re: [PATCH 1/2] mm: Introducing arch_remap hook

From: Laurent Dufour <[email-masked]>
Date: Mon, 23 Mar 2015 10:11:18 +0100

On 23/03/2015 09:52, Ingo Molnar wrote:
> 
> * Laurent Dufour <[email-masked]> wrote:
> 
>> Some architecture would like to be triggered when a memory area is moved
>> through the mremap system call.
>>
>> This patch is introducing a new arch_remap mm hook which is placed in the
>> path of mremap, and is called before the old area is unmapped (and the
>> arch_unmap hook is called).
>>
>> To no break the build, this patch adds the empty hook definition to the
>> architectures that were not using the generic hook's definition.
>>
>> Signed-off-by: Laurent Dufour <[email-masked]>
>> ---
>>  arch/s390/include/asm/mmu_context.h      | 6 ++++++
>>  arch/um/include/asm/mmu_context.h        | 5 +++++
>>  arch/unicore32/include/asm/mmu_context.h | 6 ++++++
>>  arch/x86/include/asm/mmu_context.h       | 6 ++++++
>>  include/asm-generic/mm_hooks.h           | 6 ++++++
>>  mm/mremap.c                              | 9 +++++++--
>>  6 files changed, 36 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/s390/include/asm/mmu_context.h b/arch/s390/include/asm/mmu_context.h
>> index 8fb3802f8fad..ddd861a490ba 100644
>> --- a/arch/s390/include/asm/mmu_context.h
>> +++ b/arch/s390/include/asm/mmu_context.h
>> @@ -131,4 +131,10 @@ static inline void arch_bprm_mm_init(struct mm_struct *mm,
>>  {
>>  }
>>  
>> +static inline void arch_remap(struct mm_struct *mm,
>> +			      unsigned long old_start, unsigned long old_end,
>> +			      unsigned long new_start, unsigned long new_end)
>> +{
>> +}
>> +
>>  #endif /* __S390_MMU_CONTEXT_H */
>> diff --git a/arch/um/include/asm/mmu_context.h b/arch/um/include/asm/mmu_context.h
>> index 941527e507f7..f499b017c1f9 100644
>> --- a/arch/um/include/asm/mmu_context.h
>> +++ b/arch/um/include/asm/mmu_context.h
>> @@ -27,6 +27,11 @@ static inline void arch_bprm_mm_init(struct mm_struct *mm,
>>  				     struct vm_area_struct *vma)
>>  {
>>  }
>> +static inline void arch_remap(struct mm_struct *mm,
>> +			      unsigned long old_start, unsigned long old_end,
>> +			      unsigned long new_start, unsigned long new_end)
>> +{
>> +}
>>  /*
>>   * end asm-generic/mm_hooks.h functions
>>   */
>> diff --git a/arch/unicore32/include/asm/mmu_context.h b/arch/unicore32/include/asm/mmu_context.h
>> index 1cb5220afaf9..39a0a553172e 100644
>> --- a/arch/unicore32/include/asm/mmu_context.h
>> +++ b/arch/unicore32/include/asm/mmu_context.h
>> @@ -97,4 +97,10 @@ static inline void arch_bprm_mm_init(struct mm_struct *mm,
>>  {
>>  }
>>  
>> +static inline void arch_remap(struct mm_struct *mm,
>> +			      unsigned long old_start, unsigned long old_end,
>> +			      unsigned long new_start, unsigned long new_end)
>> +{
>> +}
>> +
>>  #endif
>> diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
>> index 883f6b933fa4..75cb71f4be1e 100644
>> --- a/arch/x86/include/asm/mmu_context.h
>> +++ b/arch/x86/include/asm/mmu_context.h
>> @@ -172,4 +172,10 @@ static inline void arch_unmap(struct mm_struct *mm, struct vm_area_struct *vma,
>>  		mpx_notify_unmap(mm, vma, start, end);
>>  }
>>  
>> +static inline void arch_remap(struct mm_struct *mm,
>> +			      unsigned long old_start, unsigned long old_end,
>> +			      unsigned long new_start, unsigned long new_end)
>> +{
>> +}
>> +
>>  #endif /* _ASM_X86_MMU_CONTEXT_H */
> 
> So instead of spreading these empty prototypes around mmu_context.h 
> files, why not add something like this to the PPC definition:
> 
>  #define __HAVE_ARCH_REMAP
> 
> and define the empty prototype for everyone else? It's a bit like how 
> the __HAVE_ARCH_PTEP_* namespace works.
> 
> That should shrink this patch considerably.

My idea was to mimic the MMU hook's definition. This new hook is in the
continuity of what have been done for arch_dup_mmap, arch_exit_mmap,
arch_unmap and arch_bprm_mm_init.

Do you think that there is a need to make this one in another way ?

Thanks,
Laurent.