Subject: Re: [PATCH v3 2/2] powerpc/mm: Tracking vDSO remap

From: Ingo Molnar <[email-masked]>
Date: Wed, 25 Mar 2015 19:36:47 +0100

* Ingo Molnar <[email-masked]> wrote:

> > +#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() doesn't allow moving multiple vmas so we can limit the
> > +	 * check to old_start == vdso_base.
> > +	 */
> > +	if (old_start == mm->context.vdso_base)
> > +		mm->context.vdso_base = new_start;
> > +}
> 
> mremap() doesn't allow moving multiple vmas, but it allows the 
> movement of multi-page vmas and it also allows partial mremap()s, 
> where it will split up a vma.

I.e. mremap() supports the shrinking (and growing) of vmas. In that 
case mremap() will unmap the end of the vma and will shrink the 
remaining vDSO vma.

Doesn't that result in a non-working vDSO that should zero out 
vdso_base?

Thanks,

	Ingo