linux-kernel - Re: [PATCH 2/6] KVM MMU: fix kvm_mmu_zap

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Message-ID: <4BC2E654.7050002@cn.fujitsu.com>
Date:	Mon, 12 Apr 2010 17:22:28 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	KVM list <kvm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/6] KVM MMU: fix kvm_mmu_zap_page() and its calling path

Hi Avi,

Avi Kivity wrote:

> hlist_for_each_entry_safe() is supposed to be be safe against removal of
> the element that is pointed to by the iteration cursor.

If we destroyed the next point, hlist_for_each_entry_safe() is unsafe.

List hlist_for_each_entry_safe()'s code:

|#define hlist_for_each_entry_safe(tpos, pos, n, head, member) 		 \
|	for (pos = (head)->first;					 \
|	     pos && ({ n = pos->next; 1; }) && 				 \
|		({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \
|	     pos = n)

if n is destroyed:
'pos = n, n = pos->next'
then it access n again, it's unsafe/illegal for us.

Xiao
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