On Wed, 2015-03-25 at 19:33 +0100, Ingo Molnar wrote:
> * Laurent Dufour <ldufour@xxxxxxxxxxxxxxxxxx> wrote:
>
> > +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;
> > +}
>
> So AFAICS PowerPC can have multi-page vDSOs, right?
>
> So what happens if I munmap() the middle or end of the vDSO? The above
> condition only seems to cover unmaps that affect the first page. I
> think 'affects any page' ought to be the right condition? (But I know
> nothing about PowerPC so I might be wrong.)
You are right, we have at least two pages.
>
> > +#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 ?
Cheers,
Ben.
> Thanks,
>
> Ingo
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