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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
Date: Mon, 13 May 2019 13:22:37 +0800	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 2019/5/10 下午12:48, Jason Wang wrote:
> 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

Ok, instead of using tricks, I think we can gracefully fallback to a 
get_user()/put_user() pair protected by a mutex.

Let me post a non-rfc version for this.


      reply	other threads:[~2019-05-13  5:22 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-09 12:58 Jason Wang
2019-05-09 13:18 ` Michael S. Tsirkin
2019-05-10  2:59   ` Jason Wang
2019-05-10  4:48     ` Jason Wang
2019-05-13  5:22       ` Jason Wang [this message]

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