On Wed, May 31, 2017 at 8:03 AM, Jérôme Glisse <jglisse@xxxxxxxxxx> wrote:
> Since af2cf278ef4f ("Don't remove PGD entries in remove_pagetable()")
> we no longer cleanup stall pgd entries and thus the BUG_ON() inside
> sync_global_pgds() is wrong.
>
> This patch remove the BUG_ON() and unconditionaly update stall pgd
> entries.
>
> Signed-off-by: Jérôme Glisse <jglisse@xxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> ---
> arch/x86/mm/init_64.c | 7 +------
> 1 file changed, 1 insertion(+), 6 deletions(-)
>
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index ff95fe8..36b9020 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -123,12 +123,7 @@ void sync_global_pgds(unsigned long start, unsigned long end)
> pgt_lock = &pgd_page_get_mm(page)->page_table_lock;
> spin_lock(pgt_lock);
>
> - if (!p4d_none(*p4d_ref) && !p4d_none(*p4d))
> - BUG_ON(p4d_page_vaddr(*p4d)
> - != p4d_page_vaddr(*p4d_ref));
> -
> - if (p4d_none(*p4d))
> - set_p4d(p4d, *p4d_ref);
> + set_p4d(p4d, *p4d_ref);
If we have a mismatch in the vmalloc range, vmalloc_fault is going to
screw up and we'll end up using incorrect page tables.
What's causing the mismatch? If you're hitting this BUG in practice,
I suspect we have a bug elsewhere.
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