From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xiao Guangrong Subject: Re: [PATCH v3 01/11] KVM: MMU: avoid pte_list_desc running out in kvm_mmu_pte_write Date: Tue, 13 Sep 2011 18:24:20 +0800 Message-ID: <4E6F2F54.4030004@cn.fujitsu.com> References: <4E5C4C20.3000403@cn.fujitsu.com> <4E6F2790.4020602@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: Marcelo Tosatti , LKML , KVM To: Avi Kivity Return-path: In-Reply-To: <4E6F2790.4020602@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.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?