Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755089AbdLFLMs (ORCPT ); Wed, 6 Dec 2017 06:12:48 -0500 Received: from aserp2130.oracle.com ([141.146.126.79]:54276 "EHLO aserp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754924AbdLFLMp (ORCPT ); Wed, 6 Dec 2017 06:12:45 -0500 Date: Wed, 6 Dec 2017 06:12:37 -0500 From: Konrad Rzeszutek Wilk To: Wanpeng Li Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= , Wanpeng Li Subject: Re: [PATCH v2 1/2] KVM: MMU: Fix infinite loop when there is no available mmu page Message-ID: <20171206111237.GB28047@char.us.oracle.com> References: <1512552510-13858-1-git-send-email-wanpeng.li@hotmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <1512552510-13858-1-git-send-email-wanpeng.li@hotmail.com> User-Agent: Mutt/1.8.3 (2017-05-23) X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=8736 signatures=668641 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1712060163 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by nfs id vB6BCqek017893 Content-Length: 3020 Lines: 98 On Wed, Dec 06, 2017 at 01:28:30AM -0800, Wanpeng Li wrote: > From: Wanpeng Li > > The below test case can cause infinite loop in kvm when ept=0. > > #include > #include > #include > #include > #include > #include > #include > > long r[5]; > int main() > { > r[2] = open("/dev/kvm", O_RDONLY); > r[3] = ioctl(r[2], KVM_CREATE_VM, 0); > r[4] = ioctl(r[3], KVM_CREATE_VCPU, 7); > ioctl(r[4], KVM_RUN, 0); > } > > It doesn't setup the memory regions, mmu_alloc_shadow/direct_roots() in > kvm return 1 when kvm fails to allocate root page table which can result > in beblow infinite loop: > > vcpu_run() { > for (;;) { > r = vcpu_enter_guest()::kvm_mmu_reload() returns 1 > if (r <= 0) > break; > if (need_resched()) > cond_resched(); > } > } > > This patch fixes it by returning -ENOSPC when there is no available kvm mmu No space left? Why not ENXIO ? > page for root page table. > > Cc: Paolo Bonzini > Cc: Radim Krčmář > Fixes: 26eeb53cf0f (KVM: MMU: Bail out immediately if there is no available mmu page) > Signed-off-by: Wanpeng Li > --- > v1 -> v2: > * cleanup patch description > > arch/x86/kvm/mmu.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > index c9aaa18..89da688 100644 > --- a/arch/x86/kvm/mmu.c > +++ b/arch/x86/kvm/mmu.c > @@ -3395,7 +3395,7 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu) > spin_lock(&vcpu->kvm->mmu_lock); > if(make_mmu_pages_available(vcpu) < 0) { > spin_unlock(&vcpu->kvm->mmu_lock); > - return 1; > + return -ENOSPC; > } > sp = kvm_mmu_get_page(vcpu, 0, 0, > vcpu->arch.mmu.shadow_root_level, 1, ACC_ALL); > @@ -3410,7 +3410,7 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu) > spin_lock(&vcpu->kvm->mmu_lock); > if (make_mmu_pages_available(vcpu) < 0) { > spin_unlock(&vcpu->kvm->mmu_lock); > - return 1; > + return -ENOSPC; > } > sp = kvm_mmu_get_page(vcpu, i << (30 - PAGE_SHIFT), > i << 30, PT32_ROOT_LEVEL, 1, ACC_ALL); > @@ -3450,7 +3450,7 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu) > spin_lock(&vcpu->kvm->mmu_lock); > if (make_mmu_pages_available(vcpu) < 0) { > spin_unlock(&vcpu->kvm->mmu_lock); > - return 1; > + return -ENOSPC; > } > sp = kvm_mmu_get_page(vcpu, root_gfn, 0, > vcpu->arch.mmu.shadow_root_level, 0, ACC_ALL); > @@ -3487,7 +3487,7 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu) > spin_lock(&vcpu->kvm->mmu_lock); > if (make_mmu_pages_available(vcpu) < 0) { > spin_unlock(&vcpu->kvm->mmu_lock); > - return 1; > + return -ENOSPC; > } > sp = kvm_mmu_get_page(vcpu, root_gfn, i << 30, PT32_ROOT_LEVEL, > 0, ACC_ALL); > -- > 2.7.4 >