linux-kernel - Re: [PATCH] virt: kvm: arm: vgic: Process the failure case when kvm_register_device

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Message-ID: <5466177F.8070704@arm.com>
Date:	Fri, 14 Nov 2014 14:53:51 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Chen Gang <gang.chen.5i5j@...il.com>
CC:	"christoffer.dall@...aro.org" <christoffer.dall@...aro.org>,
	"gleb@...nel.org" <gleb@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] virt: kvm: arm: vgic: Process the failure case when kvm_register_device_ops()
 fails

On 14/11/14 14:27, Chen Gang wrote:
> On 11/14/2014 10:09 PM, Marc Zyngier wrote:
>> On 14/11/14 14:05, Chen Gang wrote:
>>> On 11/13/2014 11:30 PM, Marc Zyngier wrote:
>>>> On 13/11/14 15:04, Chen Gang wrote:
>>>>> When kvm_register_device_ops() fails, also need call free_percpu_irq()
>>>>> just like others have down within kvm_vgic_hyp_init().
>>>>>
>>>>> Signed-off-by: Chen Gang <gang.chen.5i5j@...il.com>
>>>>> ---
>>>>>  virt/kvm/arm/vgic.c | 10 ++++++++--
>>>>>  1 file changed, 8 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
>>>>> index 3aaca49..b799f17 100644
>>>>> --- a/virt/kvm/arm/vgic.c
>>>>> +++ b/virt/kvm/arm/vgic.c
>>>>> @@ -2470,8 +2470,14 @@ int kvm_vgic_hyp_init(void)
>>>>>  
>>>>>  	on_each_cpu(vgic_init_maintenance_interrupt, NULL, 1);
>>>>>  
>>>>> -	return kvm_register_device_ops(&kvm_arm_vgic_v2_ops,
>>>>> -				       KVM_DEV_TYPE_ARM_VGIC_V2);
>>>>> +	ret = kvm_register_device_ops(&kvm_arm_vgic_v2_ops,
>>>>> +				      KVM_DEV_TYPE_ARM_VGIC_V2);
>>>>> +	if (ret) {
>>>>> +		kvm_err("Cannot register device ops\n");
>>>>> +		goto out_free_irq;
>>>>> +	}
>>>>> +
>>>>> +	return 0;
>>>>>  
>>>>>  out_free_irq:
>>>>>  	free_percpu_irq(vgic->maint_irq, kvm_get_running_vcpus());
>>>>>
>>>>
>>>> Awesome. You're now freeing a per-cpu interrupt after just after having
>>>> enabled it on all CPUs. What could possibly go wrong?
>>>>
>>>
>>> OK, thanks. What you said sound reasonable to me. Need call on_each_cpu
>>> for disable_percpu_irq(). Also need call __unregister_cpu_notifier(),
>>> and need a new function vgic_arch_unsetup() for arm64.
>>
>> No. Just look at the code. Why don't you just move the
>> kvm_register_device_ops call *before* enabling the interrupt?
>>
> 
> Only based on the current code, what you said is reasonable to me.
> 
> But in the normal initializing sequence, firstly for architecture
> dependence features, then for common cpu features, at last for other
> devices (at least, other devices need be the last).
> 
> So for me, we need still remain current initializing sequence for
> extensible in the future.

Well, the current code is what matters to me, not some hypothetical
consideration about how things should (or should not) be.

If you plan to add some code that will require such a refactor, then
post the code together with whatever you want to see changed, and we can
talk about it.

Until then, I'm not willing to take something that looks over-designed
in place of a 4 line fix.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...

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