From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932402Ab1IMT3U (ORCPT ); Tue, 13 Sep 2011 15:29:20 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:56352 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S932093Ab1IMT3S (ORCPT ); Tue, 13 Sep 2011 15:29:18 -0400 Message-ID: <4E6FAFA3.4010108@cn.fujitsu.com> Date: Wed, 14 Sep 2011 03:31:47 +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> <4E6F2F54.4030004@cn.fujitsu.com> <4E6F3589.1090107@redhat.com> In-Reply-To: <4E6F3589.1090107@redhat.com> X-MIMETrack: Itemize by SMTP Server on mailserver/fnst(Release 8.5.1FP4|July 25, 2010) at 2011-09-14 03:28:05, Serialize by Router on mailserver/fnst(Release 8.5.1FP4|July 25, 2010) at 2011-09-14 03:28:05, Serialize complete at 2011-09-14 03:28:05 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 06:50 PM, Avi Kivity wrote: > On 09/13/2011 01:24 PM, Xiao Guangrong wrote: >> 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? >> > > Yes. > > btw, is rmap_can_add() sufficent? We allocate more than just rmaps in mmu_topup_memory_caches(). I guess it is, but this is getting tricky. > rmap_can_add() is used to avoid prefetching sptes more than the number of rmaps in the cache, because we do not know the exact number of sptes to be fetched. :-)