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From: Jason Wang <jasowang@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	Christoph Hellwig <hch@infradead.org>,
	James Bottomley <James.Bottomley@hansenpartnership.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Darren Hart <dvhart@infradead.org>
Subject: Re: [RFC PATCH V2] vhost: don't use kmap() to log dirty pages
Date: Fri, 10 May 2019 12:48:12 +0800	[thread overview]
Message-ID: <fa6444aa-9c46-22f0-204a-c7592dc5bd51@redhat.com> (raw)
In-Reply-To: <d6d69a36-9a3a-2a21-924e-97fdcc6e6733@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


  reply	other threads:[~2019-05-10  4:48 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 [this message]
2019-05-13  5:22       ` Jason Wang

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