Subject: Re: [PATCH v2 2/2] powerpc/mm: Tracking vDSO remap

From: Laurent Dufour <[email-masked]>
Date: Wed, 25 Mar 2015 14:25:16 +0100

On 25/03/2015 13:11, Ingo Molnar wrote:
> 
> * Laurent Dufour <[email-masked]> wrote:
> 
>> Some processes (CRIU) are moving the vDSO area using the mremap system
>> call. As a consequence the kernel reference to the vDSO base address is
>> no more valid and the signal return frame built once the vDSO has been
>> moved is not pointing to the new sigreturn address.
>>
>> This patch handles vDSO remapping and unmapping.
>>
>> Signed-off-by: Laurent Dufour <[email-masked]>
>> ---
>>  arch/powerpc/include/asm/mmu_context.h | 36 +++++++++++++++++++++++++++++++++-
>>  1 file changed, 35 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
>> index 73382eba02dc..be5dca3f7826 100644
>> --- a/arch/powerpc/include/asm/mmu_context.h
>> +++ b/arch/powerpc/include/asm/mmu_context.h
>> @@ -8,7 +8,6 @@
>>  #include <linux/spinlock.h>
>>  #include <asm/mmu.h>	
>>  #include <asm/cputable.h>
>> -#include <asm-generic/mm_hooks.h>
>>  #include <asm/cputhreads.h>
>>  
>>  /*
>> @@ -109,5 +108,40 @@ static inline void enter_lazy_tlb(struct mm_struct *mm,
>>  #endif
>>  }
>>  
>> +static inline void arch_dup_mmap(struct mm_struct *oldmm,
>> +				 struct mm_struct *mm)
>> +{
>> +}
>> +
>> +static inline void arch_exit_mmap(struct mm_struct *mm)
>> +{
>> +}
>> +
>> +static inline void arch_unmap(struct mm_struct *mm,
>> +			struct vm_area_struct *vma,
>> +			unsigned long start, unsigned long end)
>> +{
>> +	if (start <= mm->context.vdso_base && mm->context.vdso_base < end)
>> +		mm->context.vdso_base = 0;
>> +}
>> +
>> +static inline void arch_bprm_mm_init(struct mm_struct *mm,
>> +				     struct vm_area_struct *vma)
>> +{
>> +}
>> +
>> +#define __HAVE_ARCH_REMAP
>> +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)
>> +{
>> +	/*
>> +	 * mremap don't allow moving multiple vma so we can limit the check
>> +	 * to old_start == vdso_base.
> 
> s/mremap don't allow moving multiple vma
>   mremap() doesn't allow moving multiple vmas
> 
> right?

Sure you're right.

I'll provide a v3 fixing that comment.

Thanks,
Laurent.