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

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

----- hpa@zytor.com wrote:

> 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?

I considered copying stable but then I decided that this is a debugging feature
--- kernel_map_pages() is only defined if CONFIG_DEBUG_PAGEALLOC is set and my
thinking was that stable kernels usually don't do this.


-boris