Re: [PATCH] mm/x86: Flush lazy MMU when DEBUG_PAGEALLOC is set

["H. Peter Anvin" <hpa@zytor.com>]

On 02/26/2013 02:56 PM, Boris Ostrovsky wrote:
> When CONFIG_DEBUG_PAGEALLOC is set page table updates made by
> kernel_map_pages() are not made visible (via TLB flush) immediately if lazy
> MMU is on. In environments that support lazy MMU (e.g. Xen) this may lead to
> fatal page faults, for example, when zap_pte_range() needs to allocate pages
> in __tlb_remove_page() -> tlb_next_batch().
> 
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> ---
>  arch/x86/mm/pageattr.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
> index ca1f1c2..7b3216e 100644
> --- a/arch/x86/mm/pageattr.c
> +++ b/arch/x86/mm/pageattr.c
> @@ -1369,6 +1369,8 @@ void kernel_map_pages(struct page *page, int numpages, int enable)
>  	 * but that can deadlock->flush only current cpu:
>  	 */
>  	__flush_tlb_all();
> +
> +	arch_flush_lazy_mmu_mode();
>  }
>  
>  #ifdef CONFIG_HIBERNATION
> 

This sounds like a critical fix, i.e. a -stable candidate.  Am I correct?

	-hpa