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

From: Ingo Molnar <[email-masked]>
Date: Wed, 25 Mar 2015 13:11:19 +0100

* 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?

Thanks,

	Ingo