From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752102Ab1IMKV7 (ORCPT ); Tue, 13 Sep 2011 06:21:59 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:53617 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751131Ab1IMKV6 (ORCPT ); Tue, 13 Sep 2011 06:21:58 -0400 Message-ID: <4E6F2F54.4030004@cn.fujitsu.com> Date: Tue, 13 Sep 2011 18:24:20 +0800 From: Xiao Guangrong User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110428 Fedora/3.1.10-1.fc15 Thunderbird/3.1.10 MIME-Version: 1.0 To: Avi Kivity CC: Marcelo Tosatti , LKML , KVM Subject: Re: [PATCH v3 01/11] KVM: MMU: avoid pte_list_desc running out in kvm_mmu_pte_write References: <4E5C4C20.3000403@cn.fujitsu.com> <4E6F2790.4020602@redhat.com> In-Reply-To: <4E6F2790.4020602@redhat.com> X-MIMETrack: Itemize by SMTP Server on mailserver/fnst(Release 8.5.1FP4|July 25, 2010) at 2011-09-13 18:20:38, Serialize by Router on mailserver/fnst(Release 8.5.1FP4|July 25, 2010) at 2011-09-13 18:20:39, Serialize complete at 2011-09-13 18:20:39 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/13/2011 05:51 PM, Avi Kivity wrote: > On 08/30/2011 05:34 AM, Xiao Guangrong wrote: >> kvm_mmu_pte_write is unsafe since we need to alloc pte_list_desc in the >> function when spte is prefetched, unfortunately, we can not know how many >> spte need to be prefetched on this path, that means we can use out of the >> free pte_list_desc object in the cache, and BUG_ON() is triggered, also some >> path does not fill the cache, such as INS instruction emulated that does not >> trigger page fault >> >> @@ -3716,10 +3735,6 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u32 error_code, >> goto out; >> } >> >> - r = mmu_topup_memory_caches(vcpu); >> - if (r) >> - goto out; >> - >> er = x86_emulate_instruction(vcpu, cr2, 0, insn, insn_len); >> > > Suppose we are out of memory, can't this get us in an endless loop? > > return -ENOMEM breaks as out (and kills the guest, likely). > If memory is not enough, we just clear sptes on pte_write path(not prefetch spte), the later page fault path can return -1 to let guest crash. Hmm?