linux-kernel - Re: [PATCH CFT 0/4] VT-d PI fixes

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Date:   Wed, 7 Jun 2017 16:32:55 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     "Gonglei (Arei)" <arei.gonglei@...wei.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>
Cc:     longpeng <longpeng2@...wei.com>,
        "Huangweidong (C)" <weidong.huang@...wei.com>,
        "wangxin (U)" <wangxinxin.wang@...wei.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH CFT 0/4] VT-d PI fixes



On 07/06/2017 11:33, Gonglei (Arei) wrote:
> 
>> -----Original Message-----
>> From: Paolo Bonzini [mailto:paolo.bonzini@...il.com] On Behalf Of Paolo
>> Bonzini
>> Sent: Tuesday, June 06, 2017 6:57 PM
>> To: linux-kernel@...r.kernel.org; kvm@...r.kernel.org
>> Cc: longpeng; Huangweidong (C); Gonglei (Arei); wangxin (U); Radim Krčmář
>> Subject: [PATCH CFT 0/4] VT-d PI fixes
>>
>> These should fix, or at least help, the kernel panic reported by Longpeng
>> with VT-d posted interrupts.
>>
>> CONFIG_DEBUG_LIST reports a double add, meaning that pi_pre_block ran
>> twice
>> without pi_post_block deleting the vCPU from the blocked_on_vcpu list.
>> The only possibility that I could think of is that this:
>>
>>         if (!kvm_arch_has_assigned_device(vcpu->kvm) ||
>>                 !irq_remapping_cap(IRQ_POSTING_CAP)  ||
>>                 !kvm_vcpu_apicv_active(vcpu))
>>                 return;
>>
>> was false in pi_post_block.  In turn, I can only think of hot-unplug as
>> the cause of this imbalance, but maybe there is another way to reach it
>> just via repeated startup and shutdown.  Gonglei reported problems with
>> hot-unplug offlist too, so this is a start.
>>
>> In any case, patch 2 replaces it with a check on vcpu->pre_pcpu.
>> A similar change is done in patch 3 to vmx_vcpu_pi_load.  I don't
>> have hardware easily accessible with VT-d PI, so these patches are
>> compile-tested only.  I apologize for any stupid mistakes.
>>
> Hi Paolo,
> 
> We are testing your patch, but maybe need some time to report
> the results because it's not an inevitable problem.

Of course!  I guess it should run for at least a couple days before
deeming it fixed.  If you didn't find any immediate showstopper bugs,
that's already good. :)

Paolo

> Meanwhile we also try to find a possible scenario of non-hotplugging to
> explain the double-add warnings.
> 
> We found that some other VMs start failed before the kernel painc:
> 
>  2017-06-02T12:27:49.972583Z qemu-kvm: -device vfio-pci,host=0b:10.4,id=hostdev0,bus=pci.0,addr=0x5: vfio: error getting device 0000:
> 0b:10.4 from group 97: No such device
> Verify all devices in group 97 are bound to vfio-<bus> or pci-stub and not already in use
> 2017-06-02T12:27:49.975925Z qemu-kvm: -device vfio-pci,host=0b:10.4,id=hostdev0,bus=pci.0,addr=0x5: vfio: failed to get device 0000:
> 0b:10.4
> 2017-06-02T12:27:51.246385Z qemu-kvm: -device vfio-pci,host=0b:10.4,id=hostdev0,bus=pci.0,addr=0x5: Device initialization failed
> 2017-06-02 12:27:53.628: shutting down, reason=crashed
> 2017-06-02 12:30:48.723: shutting down, reason=failed
> 
> But we don't think those failure will cause the unequal of kvm->arch.assigned_device_count
> between pi_pre_block and pi_post_block. Am I right?
> 
> Thanks,
> -Gonglei
> 
>