On 2017/6/6 18:57, 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) <longpeng2@xxxxxxxxxx>
> Cc: Huangweidong <weidong.huang@xxxxxxxxxx>
> Cc: Gonglei <arei.gonglei@xxxxxxxxxx>
> Cc: wangxin <wangxinxin.wang@xxxxxxxxxx>
> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
> arch/x86/kvm/vmx.c | 62 ++++++++++++++++++++++--------------------------------
> 1 file changed, 25 insertions(+), 37 deletions(-)
>
[...]
> @@ -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));
Hi Paolo,
spin_lock_irqsave() will disable kernel preempt, but spin_lock() won't. is there
some potential problems ?
Regards,
Longpeng(Mike)
> 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;
> - }
> -
> 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);
> +
> + local_irq_enable();
> + return (vcpu->pre_pcpu == -1);
> }
>
> 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)
--
Regards,
Longpeng(Mike)
