From mboxrd@z Thu Jan  1 00:00:00 1970
From: Takuya Yoshikawa <takuya.yoshikawa@gmail.com>
Subject: Re: [test result] dirty logging without srcu update -- Re:
 [RFC][PATCH] srcu: Implement call_srcu()
Date: Thu, 2 Feb 2012 23:44:50 +0900
Message-ID: <20120202234450.20b75999de0e3b05043ffb71@gmail.com>
References: <1328016724.2446.229.camel@twins>
	<4F27F0E6.1040309@redhat.com>
	<1328017807.2446.230.camel@twins>
	<20120131222447.GH2391@linux.vnet.ibm.com>
	<1328091749.2760.34.camel@laptop>
	<4F29178A.1090306@redhat.com>
	<4F2918D5.4050104@redhat.com>
	<4F291B56.30600@oss.ntt.co.jp>
	<4F291B92.8070402@redhat.com>
	<4F291E1F.3030505@oss.ntt.co.jp>
	<4F293D14.5030008@redhat.com>
	<20120202144633.1fc9b997.yoshikawa.takuya@oss.ntt.co.jp>
	<4F2A611E.6090005@redhat.com>
	<4F2A63B9.8000405@oss.ntt.co.jp>
	<4F2A63C6.7030301@redhat.com>
	<4F2A682C.7090109@oss.ntt.co.jp>
	<4F2A6D46.6010406@redhat.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Cc: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>,
	Peter Zijlstra <peterz@infradead.org>,
	paulmck@linux.vnet.ibm.com, Oleg Nesterov <oleg@redhat.com>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	KVM list <kvm@vger.kernel.org>
To: Avi Kivity <avi@redhat.com>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <4F2A6D46.6010406@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
List-Id: kvm.vger.kernel.org

Avi Kivity <avi@redhat.com> wrote:

> > I have one concern about correctness issue though:
> >
> >     concurrent rmap write protection may not be safe due to
> >     delayed tlb flush ... cannot happen?
> 
> What do you mean by concurrent rmap write protection?
> 

Not sure, but other codes like:

- mmu_sync_children()
	for_each_sp(pages, sp, parents, i)
		protected |= rmap_write_protect(vcpu->kvm, sp->gfn);

		if (protected)
			kvm_flush_remote_tlbs(vcpu->kvm);

- kvm_mmu_get_page()
	if (rmap_write_protect(vcpu->kvm, gfn))
		kvm_flush_remote_tlbs(vcpu->kvm);

I just wondered what can happen if GET_DIRTY_LOG is being processed
behind these processing?

They may find nothing to write protect and won't do kvm_flush_remote_tlbs()
if the gfn has been already protected by GET_DIRTY_LOG.

But GET_DIRTY_LOG may still be busy write protecting other pages and
others can return before.  (My code releases mmu_lock to not include
__put_user() in the critical section.)

I am not still enough familier with these code yet.
(maybe empty concern)

	Takuya