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Date:   Fri, 10 May 2019 12:48:12 +0800
From:   Jason Wang <>
To:     "Michael S. Tsirkin" <>
        Christoph Hellwig <>,
        James Bottomley <>,
        Andrea Arcangeli <>,
        Thomas Gleixner <>,
        Ingo Molnar <>,
        Peter Zijlstra <>,
        Darren Hart <>
Subject: Re: [RFC PATCH V2] vhost: don't use kmap() to log dirty pages

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.


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