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

[Dan Williams]

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>