From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH v3 01/11] KVM: MMU: avoid pte_list_desc running out in kvm_mmu_pte_write Date: Tue, 13 Sep 2011 13:50:49 +0300 Message-ID: <4E6F3589.1090107@redhat.com> References: <4E5C4C20.3000403@cn.fujitsu.com> <4E6F2790.4020602@redhat.com> <4E6F2F54.4030004@cn.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Marcelo Tosatti , LKML , KVM To: Xiao Guangrong Return-path: In-Reply-To: <4E6F2F54.4030004@cn.fujitsu.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org 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. -- error compiling committee.c: too many arguments to function