On Thu, Jun 08, 2017 at 03:00:39AM -0400, Paolo Bonzini wrote: > > > ----- Original Message ----- > > From: "Peter Xu" <pet...@redhat.com> > > To: "Paolo Bonzini" <pbonz...@redhat.com> > > Cc: linux-kernel@vger.kernel.org, k...@vger.kernel.org, "Longpeng" > > <longpe...@huawei.com>, "Huangweidong" > > <weidong.hu...@huawei.com>, "Gonglei" <arei.gong...@huawei.com>, "wangxin" > > <wangxinxin.w...@huawei.com>, "Radim > > Krčmář" <rkrc...@redhat.com> > > Sent: Thursday, June 8, 2017 8:50:57 AM > > Subject: Re: [PATCH 2/4] KVM: VMX: avoid double list add with VT-d posted > > interrupts > > > > On Tue, Jun 06, 2017 at 12:57:05PM +0200, Paolo Bonzini wrote: > > > In some cases, for example involving hot-unplug of assigned > > > devices, pi_post_block can forget to remove the vCPU from the > > > blocked_vcpu_list. When this happens, the next call to > > > pi_pre_block corrupts the list. > > > > > > Fix this in two ways. First, check vcpu->pre_pcpu in pi_pre_block > > > and WARN instead of adding the element twice in the list. Second, > > > always do the list removal in pi_post_block if vcpu->pre_pcpu is > > > set (not -1). > > > > > > The new code keeps interrupts disabled for the whole duration of > > > pi_pre_block/pi_post_block. This is not strictly necessary, but > > > easier to follow. For the same reason, PI.ON is checked only > > > after the cmpxchg, and to handle it we just call the post-block > > > code. This removes duplication of the list removal code. > > > > > > Cc: Longpeng (Mike) <longpe...@huawei.com> > > > Cc: Huangweidong <weidong.hu...@huawei.com> > > > Cc: Gonglei <arei.gong...@huawei.com> > > > Cc: wangxin <wangxinxin.w...@huawei.com> > > > Cc: Radim Krčmář <rkrc...@redhat.com> > > > Signed-off-by: Paolo Bonzini <pbonz...@redhat.com> > > > --- > > > arch/x86/kvm/vmx.c | 62 > > > ++++++++++++++++++++++-------------------------------- > > > 1 file changed, 25 insertions(+), 37 deletions(-) > > > > > > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c > > > index 747d16525b45..0f4714fe4908 100644 > > > --- a/arch/x86/kvm/vmx.c > > > +++ b/arch/x86/kvm/vmx.c > > > @@ -11236,10 +11236,11 @@ static void __pi_post_block(struct kvm_vcpu > > > *vcpu) > > > struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu); > > > struct pi_desc old, new; > > > unsigned int dest; > > > - unsigned long flags; > > > > > > do { > > > old.control = new.control = pi_desc->control; > > > + WARN(old.nv != POSTED_INTR_WAKEUP_VECTOR, > > > + "Wakeup handler not enabled while the VCPU is blocked\n"); > > > > > > dest = cpu_physical_id(vcpu->cpu); > > > > > > @@ -11256,14 +11257,10 @@ static void __pi_post_block(struct kvm_vcpu > > > *vcpu) > > > } while (cmpxchg(&pi_desc->control, old.control, > > > new.control) != old.control); > > > > > > - if(vcpu->pre_pcpu != -1) { > > > - spin_lock_irqsave( > > > - &per_cpu(blocked_vcpu_on_cpu_lock, > > > - vcpu->pre_pcpu), flags); > > > + if (!WARN_ON_ONCE(vcpu->pre_pcpu == -1)) { > > > + spin_lock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu)); > > > list_del(&vcpu->blocked_vcpu_list); > > > - spin_unlock_irqrestore( > > > - &per_cpu(blocked_vcpu_on_cpu_lock, > > > - vcpu->pre_pcpu), flags); > > > + spin_unlock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu)); > > > vcpu->pre_pcpu = -1; > > > } > > > } > > > @@ -11283,7 +11280,6 @@ static void __pi_post_block(struct kvm_vcpu *vcpu) > > > */ > > > static int pi_pre_block(struct kvm_vcpu *vcpu) > > > { > > > - unsigned long flags; > > > unsigned int dest; > > > struct pi_desc old, new; > > > struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu); > > > @@ -11293,34 +11289,20 @@ static int pi_pre_block(struct kvm_vcpu *vcpu) > > > !kvm_vcpu_apicv_active(vcpu)) > > > return 0; > > > > > > - vcpu->pre_pcpu = vcpu->cpu; > > > - spin_lock_irqsave(&per_cpu(blocked_vcpu_on_cpu_lock, > > > - vcpu->pre_pcpu), flags); > > > - list_add_tail(&vcpu->blocked_vcpu_list, > > > - &per_cpu(blocked_vcpu_on_cpu, > > > - vcpu->pre_pcpu)); > > > - spin_unlock_irqrestore(&per_cpu(blocked_vcpu_on_cpu_lock, > > > - vcpu->pre_pcpu), flags); > > > + WARN_ON(irqs_disabled()); > > > + local_irq_disable(); > > > + if (!WARN_ON_ONCE(vcpu->pre_pcpu != -1)) { > > > + vcpu->pre_pcpu = vcpu->cpu; > > > + spin_lock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu)); > > > + list_add_tail(&vcpu->blocked_vcpu_list, > > > + &per_cpu(blocked_vcpu_on_cpu, > > > + vcpu->pre_pcpu)); > > > + spin_unlock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu)); > > > + } > > > > > > do { > > > old.control = new.control = pi_desc->control; > > > > > > - /* > > > - * We should not block the vCPU if > > > - * an interrupt is posted for it. > > > - */ > > > - if (pi_test_on(pi_desc) == 1) { > > > - spin_lock_irqsave(&per_cpu(blocked_vcpu_on_cpu_lock, > > > - vcpu->pre_pcpu), flags); > > > - list_del(&vcpu->blocked_vcpu_list); > > > - spin_unlock_irqrestore( > > > - &per_cpu(blocked_vcpu_on_cpu_lock, > > > - vcpu->pre_pcpu), flags); > > > - vcpu->pre_pcpu = -1; > > > - > > > - return 1; > > > > [1] > > > > > - } > > > - > > > WARN((pi_desc->sn == 1), > > > "Warning: SN field of posted-interrupts " > > > "is set before blocking\n"); > > > @@ -11345,7 +11327,12 @@ static int pi_pre_block(struct kvm_vcpu *vcpu) > > > } while (cmpxchg(&pi_desc->control, old.control, > > > new.control) != old.control); > > > > > > - return 0; > > > + /* We should not block the vCPU if an interrupt is posted for it. */ > > > + if (pi_test_on(pi_desc) == 1) > > > + __pi_post_block(vcpu); > > > > A question on when pi_test_on() is set: > > > > The old code will return 1 if detected (ses [1]), while the new code > > does not. Would that matter? (IIUC that decides whether the vcpu will > > continue to run?) > > The new code does, because __pi_post_block resets vcpu->pre_pcpu to -1.
Sorry I overlook that. :-) > > > > + > > > + local_irq_enable(); > > > + return (vcpu->pre_pcpu == -1); > > > > Above we have: > > > > if (!WARN_ON_ONCE(vcpu->pre_pcpu != -1)) { > > vcpu->pre_pcpu = vcpu->cpu; > > ... > > } > > > > Then can here vcpu->pre_pcpu really be -1? > > See above. :) Yes. Then there's no problem. > > > > } > > > > > > static int vmx_pre_block(struct kvm_vcpu *vcpu) > > > @@ -11361,12 +11348,13 @@ static int vmx_pre_block(struct kvm_vcpu *vcpu) > > > > > > static void pi_post_block(struct kvm_vcpu *vcpu) > > > { > > > - if (!kvm_arch_has_assigned_device(vcpu->kvm) || > > > - !irq_remapping_cap(IRQ_POSTING_CAP) || > > > - !kvm_vcpu_apicv_active(vcpu)) > > > + if (vcpu->pre_pcpu == -1) > > > return; > > > > > > + WARN_ON(irqs_disabled()); > > > + local_irq_disable(); > > > __pi_post_block(vcpu); > > > + local_irq_enable(); > > > } > > > > > > static void vmx_post_block(struct kvm_vcpu *vcpu) > > > -- > > > 2.13.0 > > > > > > > > > > A general question to pre_block/post_block handling for PI: > > > > I see that we are handling PI logic mostly in four places: > > > > vmx_vcpu_pi_{load|put} > > pi_{pre_post}_block > > > > But do we really need the pre_block/post_block handling? Here's how I > > understand when vcpu blocked: > > > > - vcpu_block > > - ->pre_block > > - kvm_vcpu_block [1] > > - schedule() > > - kvm_sched_out > > - vmx_vcpu_pi_put [3] > > - (another process working) ... > > - kvm_sched_in > > - vmx_vcpu_pi_load [4] > > - ->post_block [2] > > > > If so, [1] & [2] will definitely be paired with [3] & [4], then why we > > need [3] & [4] at all? > > > > (Though [3] & [4] will also be used when preemption happens, so they > > are required) > > > > Please kindly figure out if I missed anything important... > > Oh, I see what you mean: set up the wakeup handler in vmx_vcpu_pi_put > and rely on PI.ON to wake up the sleeping process immediately. That > should be feasible, but overall I like the current pre_block/post_block > structure, and I think it's simpler. The only thing to be careful about > is leaving the IRTE unmodified when scheduling out a blocked VCPU, which > is cleaned up and simplified in patch 3. > > So I understand that the state may seem a bit too complicated as > of this patch, but hopefully the next two make it clearer. After re-read the codes and patches I got the point. Indeed current way should be clearer since pre/post_block are mostly handling NV/DST while pi_load/put are for SN bit. Thanks! -- Peter Xu