* Benjamin Herrenschmidt <b...@kernel.crashing.org> 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.
> >
> > In particular, what happens if an mremap() is done with
> > old_start == vdso_base, but a shorter end than the end of the vDSO?
> > (i.e. a partial mremap() with fewer pages than the vDSO size)
>
> Is there a way to forbid splitting ? Does x86 deal with that case at
> all or it doesn't have to for some other reason ?
So we use _install_special_mapping() - maybe PowerPC does that too?
That adds VM_DONTEXPAND which ought to prevent some - but not all - of
the VM API weirdnesses.
On x86 we'll just dump core if someone unmaps the vdso.
Thanks,
Ingo
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