linux-kernel - Re: [PATCH v2] KVM: arm/arm64: vgic-its: Fix vgicv4 init

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Date:   Fri, 12 Jan 2018 08:45:31 +0100
From:   Auger Eric <eric.auger@...hat.com>
To:     Christoffer Dall <christoffer.dall@...aro.org>
Cc:     eric.auger.pro@...il.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, kvmarm@...ts.cs.columbia.edu,
        marc.zyngier@....com, cdall@...aro.org
Subject: Re: [PATCH v2] KVM: arm/arm64: vgic-its: Fix vgicv4 init

Hi Christoffer

On 11/01/18 19:55, Christoffer Dall wrote:
> On Mon, Jan 08, 2018 at 10:52:54AM +0100, Eric Auger wrote:
>> Commit 3d1ad640f8c94 ("KVM: arm/arm64: Fix GICv4 ITS initialization
>> issues") moved the vgic_supports_direct_msis() check in vgic_v4_init().
>> However when vgic_v4_init is called from vgic_its_create(), the has_its
>> field is not yet set. Hence vgic_supports_direct_msis returns false and
>> vgic_v4_init does nothing.
>>
>> Let's move the check back to vgic_v4_init caller.
>>
>> Fixes: 3d1ad640f8c94 ("KVM: arm/arm64: Fix GICv4 ITS initialization issues")
>> Signed-off-by: Eric Auger <eric.auger@...hat.com>
>>
>> ---
>>
>> v1 -> v2:
>> - move the check to the caller
> 
> Why this change, I slightly preferred the first version of this patch,
> but I will admit that the "has_its = true; no_wait(); has_its = false;"
> things is pretty ugly...

I didn't find the 1st solution elegant either and reverted to how the
code looked like before your patch.
> 
>> - identify the right commit this patch fixes
>> ---
>>  virt/kvm/arm/vgic/vgic-init.c | 8 +++++---
>>  virt/kvm/arm/vgic/vgic-its.c  | 2 +-
>>  virt/kvm/arm/vgic/vgic-v4.c   | 3 ---
>>  3 files changed, 6 insertions(+), 7 deletions(-)
>>
>> diff --git a/virt/kvm/arm/vgic/vgic-init.c b/virt/kvm/arm/vgic/vgic-init.c
>> index 6231012..40be908 100644
>> --- a/virt/kvm/arm/vgic/vgic-init.c
>> +++ b/virt/kvm/arm/vgic/vgic-init.c
>> @@ -285,9 +285,11 @@ int vgic_init(struct kvm *kvm)
>>  	if (ret)
>>  		goto out;
>>  
>> -	ret = vgic_v4_init(kvm);
>> -	if (ret)
>> -		goto out;
>> +	if (vgic_supports_direct_msis(kvm)) {
>> +		ret = vgic_v4_init(kvm);
>> +		if (ret)
>> +			goto out;
>> +	}
>>  
>>  	kvm_for_each_vcpu(i, vcpu, kvm)
>>  		kvm_vgic_vcpu_enable(vcpu);
>> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
>> index 8e633bd..aebc88d 100644
>> --- a/virt/kvm/arm/vgic/vgic-its.c
>> +++ b/virt/kvm/arm/vgic/vgic-its.c
>> @@ -1687,7 +1687,7 @@ static int vgic_its_create(struct kvm_device *dev, u32 type)
>>  	if (!its)
>>  		return -ENOMEM;
>>  
>> -	if (vgic_initialized(dev->kvm)) {
>> +	if (kvm_vgic_global_state.has_gicv4 && vgic_initialized(dev->kvm)) {
> 
> ... but now we're using vgic_supports_direct_msis() in one part of the
> init path and a half-open coded version of that in another path, which
> is not very pretty.
> 
> So I actually would suggest doing the init stuff more open-coded,
> because init of the gic/its/gicv4 is a mess anyway.
> 
> Something like this:
> 
> diff --git a/virt/kvm/arm/vgic/vgic-init.c b/virt/kvm/arm/vgic/vgic-init.c
> index 62310122ee78..743ca5cb05ef 100644
> --- a/virt/kvm/arm/vgic/vgic-init.c
> +++ b/virt/kvm/arm/vgic/vgic-init.c
> @@ -285,9 +285,11 @@ int vgic_init(struct kvm *kvm)
>  	if (ret)
>  		goto out;
>  
> -	ret = vgic_v4_init(kvm);
> -	if (ret)
> -		goto out;
> +	if (vgic_has_its(kvm)) {
> +		ret = vgic_v4_init(kvm);
> +		if (ret)
> +			goto out;
> +	}
>  
>  	kvm_for_each_vcpu(i, vcpu, kvm)
>  		kvm_vgic_vcpu_enable(vcpu);
> diff --git a/virt/kvm/arm/vgic/vgic-v4.c b/virt/kvm/arm/vgic/vgic-v4.c
> index 4a37292855bc..bc4265154bac 100644
> --- a/virt/kvm/arm/vgic/vgic-v4.c
> +++ b/virt/kvm/arm/vgic/vgic-v4.c
> @@ -118,7 +118,7 @@ int vgic_v4_init(struct kvm *kvm)
>  	struct kvm_vcpu *vcpu;
>  	int i, nr_vcpus, ret;
>  
> -	if (!vgic_supports_direct_msis(kvm))
> +	if (!kvm_vgic_global_state.has_gicv4)
>  		return 0; /* Nothing to see here... move along. */
>  
>  	if (dist->its_vm.vpes)
> 
> Does that work?
Looks OK to me. Unfortunately I don't have access to this specific
machine anymore at the moment so I can't test it right now.

Thanks

Eric
> 
> Thanks,
> -Christoffer
>