lkml.org 
[lkml]   [2017]   [Jun]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 2/4] KVM: VMX: avoid double list add with VT-d posted interrupts
From
Date


On 06/06/2017 14:30, Longpeng (Mike) wrote:
>
>
> 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@huawei.com>
>> Cc: Huangweidong <weidong.huang@huawei.com>
>> Cc: Gonglei <arei.gonglei@huawei.com>
>> Cc: wangxin <wangxinxin.wang@huawei.com>
>> Cc: Radim Krčmář <rkrcmar@redhat.com>
>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>> ---
>> 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 ?

Hi,

This function (and pi_pre_block too's part where it takes the spin lock)
runs with interrupts disabled now.

Thanks,

Paolo

> 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)
>
>

\
 
 \ /
  Last update: 2017-06-12 00:46    [W:0.200 / U:1.236 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site