Re: [RFC PATCH V2] vhost: don't use kmap() to log dirty pages

[Jason Wang <jasowang@redhat.com>]

On 2019/5/10 上午10:59, Jason Wang wrote:
>>>
>>>         r = get_user_pages_fast(log, 1, 1, &page);
>> OK so the trick is that page is pinned so you don't expect
>> arch_futex_atomic_op_inuser below to fail.  get_user_pages_fast
>> guarantees page is not going away but does it guarantee PTE won't be
>> invaidated or write protected?
>
>
> Good point, then I think we probably need to do manual fixup through 
> fixup_user_fault() if arch_futex_atomic_op_in_user() fail. 


This looks like a overkill, we don't need to atomic environment here 
actually. Instead, just keep pagefault enabled should work. So just 
introduce arch_futex_atomic_op_inuser_inatomic() variant with pagefault 
disabled there just for futex should be sufficient.

Thanks