linux-kernel - Re: [PATCH] kvm: arm/arm64 : fix vm's hanging at startup time

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Date:   Thu, 15 Nov 2018 11:10:30 +0000
From:   Julien Thierry <julien.thierry@....com>
To:     peng.hao2@....com.cn
Cc:     christoffer.dall@....com, marc.zyngier@....com,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kvm: arm/arm64 : fix vm's hanging at startup time



On 15/11/18 10:22, peng.hao2@....com.cn wrote:
>> Hi Peng,
>>
>> On 15/11/18 15:14, Peng Hao wrote:
>>> When virtual machine starts, hang up. The kernel version of guest
>>> is 4.16. Host support vgic_v3.
>>
>> I don't understand the issue here. the vgic_irq->group field does not
>> exist in 4.16 (neither in the first nor the last version). Nor does the
>> line you are modifying.
> Guest's kernel version is 4.16 and Host's kernel version is mainline.
> vgic_irq is a structure of Host's kvm.
>>
>> Both exist in mainline, but what you are mentioning shouldn't be an
>> issue in mainline since vgic_irq->group gets initialized in
>> kvm_vgic_vcpu_init for SGIs and PPIs (i.e. intid < 32) which includes
>> your interrupt.
> Initialization sequence of several components is like this;
> 1.       kvm_vgic_vcpu_init ---- here, dist is not initialized at this time.
>                                               and the value of irq->group depends on
>                                                dist->vgic_model. but now dist->vgic_model = 0
>                                                 and irq->group=0.
>   2.      vgic_create         -----  assign to dist->vgic_model.
>   3.     kvm_vgic_dist_init
> 

I see, thanks for explaining.

This means the initialization in kvm_vgic_vcpu_init depends on whether 
userland creates the GIC device first or the vcpus first...

I don't think the issue lies in vgic_v3_populate_lr, but in 
kvm_vgic_vcpu_init which clearly expects dist->vgic_model to be 
initialized in two places. However, the comment at the top of 
vgic-init.c states:

  * CPU Interface: 
 
 

  * 
 
 

  * - kvm_vgic_vcpu_init(): initialization of static data that 
 
 

  *   doesn't depend on any sizing information or emulation type. No 
 
 

  *   allocation is allowed there.

So I don't think we're supposed to check for dist->vgic_model here. 
Those two checks should probably be moved elsewhere (maybe in 
kvm_vgic_vcpu_enable?) once the gic type has been set.

Thanks,

> thanks.
>>
>> Cheers,
>>
>>> It was mainly due to the incorrect vgic_irq's(intid=27) group value
>>> during injection interruption. when kvm_vgic_vcpu_init is called,
>>> dist is not initialized at this time. Unable to get vgic V3 or V2
>>> correctly, so group is not set.
>>> group is setted to 1 when vgic_mmio_write_group is invoked at some
>>> time.
>>> when irq->group=0 (intid=27), No ICH_LR_GROUP flag was set and
>>> interrupt injection failed.
>>>
>>> Signed-off-by: Peng Hao <peng.hao2@....com.cn>
>>> ---
>>>    virt/kvm/arm/vgic/vgic-v3.c | 2 +-
>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/virt/kvm/arm/vgic/vgic-v3.c b/virt/kvm/arm/vgic/vgic-v3.c
>>> index 9c0dd23..d101000 100644
>>> --- a/virt/kvm/arm/vgic/vgic-v3.c
>>> +++ b/virt/kvm/arm/vgic/vgic-v3.c
>>> @@ -198,7 +198,7 @@ void vgic_v3_populate_lr(struct kvm_vcpu *vcpu, struct vgic_irq *irq, int lr)
>>>        if (vgic_irq_is_mapped_level(irq) && (val & ICH_LR_PENDING_BIT))
>>>            irq->line_level = false;
>>>
>>> -    if (irq->group)
>>> +    if (model == KVM_DEV_TYPE_ARM_VGIC_V3)
>>>            val |= ICH_LR_GROUP;
>>>
>>>        val |= (u64)irq->priority << ICH_LR_PRIORITY_SHIFT;
>>>
>>
>> --
>> Julien Thierry

-- 
Julien Thierry