Re: [PATCH] x86/mm/64: Fix crash in remove_pagetable()

[Ingo Molnar]

* Dan Williams <dan.j.williams@xxxxxxxxx> wrote:

> On Tue, Apr 25, 2017 at 2:25 AM, Kirill A. Shutemov
> <kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
> > remove_pagetable() does page walk using p*d_page_vaddr() plus cast.
> > It's not canonical approach -- we usually use p*d_offset() for that.
> >
> > It works fine as long as all page table levels are present. We broke the
> > invariant by introducing folded p4d page table level.
> >
> > As result, remove_pagetable() interprets PMD as PUD and it leads to
> > crash:
> >
> >         BUG: unable to handle kernel paging request at ffff880300000000
> >         IP: memchr_inv+0x60/0x110
> >         PGD 317d067
> >         P4D 317d067
> >         PUD 3180067
> >         PMD 33f102067
> >         PTE 8000000300000060
> >
> > Let's fix this by using p*d_offset() instead of p*d_page_vaddr() for
> > page walk.
> >
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > Reported-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> > Fixes: f2a6a7050109 ("x86: Convert the rest of the code to support p4d_t")
> 
> Thanks! This patch on top of tip/master passes a full run of the
> nvdimm regression suite.
> 
> Tested-by: Dan Williams <dan.j.williams@xxxxxxxxx>

Does a re-application of:

  "x86/mm/gup: Switch GUP to the generic get_user_page_fast() implementation"

still work (which you can achive via 'git revert 6dd29b3df975'), or is that 
another breakage?

Thanks,

	Ingo