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

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Date:   Wed, 7 Jun 2017 09:33:20 +0000
From:   "Gonglei (Arei)" <arei.gonglei@...wei.com>
To:     Paolo Bonzini <pbonzini@...hat.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


> -----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.

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