From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 2/6] KVM MMU: fix kvm_mmu_zap_page() and its calling path Date: Mon, 12 Apr 2010 15:49:21 +0300 Message-ID: <4BC316D1.3030009@redhat.com> References: <4BC2D2E2.1030604@cn.fujitsu.com> <4BC2D345.100@cn.fujitsu.com> <4BC2D8D6.6030306@redhat.com> <4BC2DFA0.6000609@cn.fujitsu.com> <4BC2E2FF.9020005@redhat.com> <4BC2E654.7050002@cn.fujitsu.com> <4BC2F536.70808@redhat.com> <4BC310A0.3090005@cn.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Marcelo Tosatti , KVM list , LKML To: Xiao Guangrong Return-path: In-Reply-To: <4BC310A0.3090005@cn.fujitsu.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 04/12/2010 03:22 PM, Xiao Guangrong wrote: > >> But kvm_mmu_zap_page() will only destroy sp == tpos == pos; n points at >> pos->next already, so it's safe. >> >> > kvm_mmu_zap_page(sp) not only zaps sp but also zaps all sp's unsync children > pages, if n is just sp's unsyc child, just at the same hlist and just behind sp, > it will crash. :-) > Ouch. I see now, thanks for explaining. One way to fix it is to make kvm_mmu_zap_page() only zap the page it is given, and use sp->role.invalid on its children. But it's better to fix it now quickly and do the more involved fixes later. Just change the assignment to a 'goto restart;' please, I don't like playing with list_for_each internals. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.