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SubjectRe: [PATCH] mm/x86: Flush lazy MMU when DEBUG_PAGEALLOC is set
Greg, policy opinion?

-hpa

On 02/26/2013 03:57 PM, Boris Ostrovsky wrote:
>
> ----- 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
>



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