linux-kernel - Re: [PATCH v2] virt: kvm: arm: vgic: Process the failure case when kvm_register_device

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Date:	Fri, 14 Nov 2014 15:55:36 +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@....linux.org.uk" <linux@....linux.org.uk>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Will Deacon <Will.Deacon@....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 v2] virt: kvm: arm: vgic: Process the failure case when
 kvm_register_device_ops() fails

On 14/11/14 15:18, Chen Gang wrote:
> When kvm_register_device_ops() fails, need disable_percpu_irq(), need
> vgic_arch_unsetup(), need __unregister_cpu_notifier(), and also need
> free_percpu_irq().
> 
> At present, there is no vgic_arch_unsetup(), so add it for resetting
> '__vgic_sr_vectors'.
> 
> 
> Signed-off-by: Chen Gang <gang.chen.5i5j@...il.com>
> ---
>  arch/arm/include/asm/kvm_host.h   |  1 +
>  arch/arm64/include/asm/kvm_host.h |  8 ++++++++
>  virt/kvm/arm/vgic.c               | 19 +++++++++++++++++--
>  3 files changed, 26 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index 53036e2..f68e302 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -232,6 +232,7 @@ static inline void vgic_arch_setup(const struct vgic_params *vgic)
>  {
>  	BUG_ON(vgic->type != VGIC_V2);
>  }
> +static inline void vgic_arch_unsetup(void) {}
>  
>  int kvm_perf_init(void);
>  int kvm_perf_teardown(void);
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 2012c4b..597500c 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -248,6 +248,14 @@ static inline void vgic_arch_setup(const struct vgic_params *vgic)
>  	}
>  }
>  
> +static inline void vgic_arch_unsetup(void)
> +{
> +	extern struct vgic_sr_vectors __vgic_sr_vectors;
> +
> +	__vgic_sr_vectors.save_vgic	= 0;
> +	__vgic_sr_vectors.restore_vgic	= 0;
> +}
> +
>  static inline void kvm_arch_hardware_disable(void) {}
>  static inline void kvm_arch_hardware_unsetup(void) {}
>  static inline void kvm_arch_sync_events(struct kvm *kvm) {}
> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
> index 3aaca49..bab81f7 100644
> --- a/virt/kvm/arm/vgic.c
> +++ b/virt/kvm/arm/vgic.c
> @@ -2405,6 +2405,11 @@ static void vgic_init_maintenance_interrupt(void *info)
>  	enable_percpu_irq(vgic->maint_irq, 0);
>  }
>  
> +static void vgic_uninit_maintenance_interrupt(void *info)
> +{
> +	disable_percpu_irq(vgic->maint_irq);
> +}
> +
>  static int vgic_cpu_notify(struct notifier_block *self,
>  			   unsigned long action, void *cpu)
>  {
> @@ -2470,9 +2475,19 @@ 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_disable_irq;
> +	}
> +
> +	return 0;
>  
> +out_disable_irq:
> +	on_each_cpu(vgic_uninit_maintenance_interrupt, NULL, 1);
> +	vgic_arch_unsetup();
> +	__unregister_cpu_notifier(&vgic_cpu_nb);
>  out_free_irq:
>  	free_percpu_irq(vgic->maint_irq, kvm_get_running_vcpus());
>  	return ret;
> 

No. This is completely overdesigned, and fixes something that really
cannot happen. What is wrong with:

diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
index 3aaca49..b7dffa80 100644
--- a/virt/kvm/arm/vgic.c
+++ b/virt/kvm/arm/vgic.c
@@ -2465,13 +2465,17 @@ int kvm_vgic_hyp_init(void)
 		goto out_free_irq;
 	}
 
+	ret = kvm_register_device_ops(&kvm_arm_vgic_v2_ops,
+				       KVM_DEV_TYPE_ARM_VGIC_V2);
+	if (ret)
+		goto out_free_irq;
+
 	/* Callback into for arch code for setup */
 	vgic_arch_setup(vgic);
 
 	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);
+	return 0;
 
 out_free_irq:
 	free_percpu_irq(vgic->maint_irq, kvm_get_running_vcpus());

This achieves the exact same effect.

Thanks,

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

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