On Thu, 15 May 2014 11:18:29 +0800 Hillf Danton <dhillf@xxxxxxxxx> wrote:
> > --- a/arch/x86/vdso/vma.c
> > +++ b/arch/x86/vdso/vma.c
> > @@ -90,6 +90,7 @@ static int map_vdso(const struct vdso_image *image, bool calculate_addr)
> > struct vm_area_struct *vma;
> > unsigned long addr;
> > int ret = 0;
> > + static struct page *no_pages[] = {NULL};
> >
> > if (calculate_addr) {
> > addr = vdso_addr(current->mm->start_stack,
> > @@ -125,7 +126,7 @@ static int map_vdso(const struct vdso_image *image, bool calculate_addr)
> > addr + image->size,
> > image->sym_end_mapping - image->size,
> > VM_READ,
> > - NULL);
> > + no_pages);
> >
> > if (IS_ERR(vma)) {
> > ret = PTR_ERR(vma);
> > --
> > 1.9.0
> >
> As the comment says,
> /*
> * Called with mm->mmap_sem held for writing.
> * Insert a new vma covering the given region, with the given flags.
> * Its pages are supplied by the given array of struct page *.
> * The array can be shorter than len >> PAGE_SHIFT if it's null-terminated.
> * The region past the last page supplied will always produce SIGBUS.
> * The array pointer and the pages it points to are assumed to stay alive
> * for as long as this mapping might exist.
> */
> struct vm_area_struct *_install_special_mapping(struct mm_struct *mm,
> unsigned long addr, unsigned long len,
> unsigned long vm_flags, struct page **pages)
> {
>
> we can send sigbus at fault time if no pages are supplied at install time.
Yes, but the way to communicate "no pages" is to pass (*pages)==NULL.
Passing (pages)==NULL causes the code to oops at fault time.
We could easily change the interface so that pages==NULL means "no
pages" but that isn't the way it works at present.
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