linux-kernel - Re: [PATCH v2 04/10] KVM: arm: guest debug, add stub KVM_SET_GUEST

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Date:	Wed, 1 Apr 2015 17:55:29 +0200
From:	David Hildenbrand <dahi@...ux.vnet.ibm.com>
To:	Alex Bennée <alex.bennee@...aro.org>
Cc:	kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.cs.columbia.edu, christoffer.dall@...aro.org,
	marc.zyngier@....com, peter.maydell@...aro.org, agraf@...e.de,
	drjones@...hat.com, pbonzini@...hat.com, zhichao.huang@...aro.org,
	jan.kiszka@...mens.com, r65777@...escale.com, bp@...e.de,
	Gleb Natapov <gleb@...nel.org>,
	Jonathan Corbet <corbet@....net>,
	Russell King <linux@....linux.org.uk>,
	linux-doc@...r.kernel.org (open list:DOCUMENTATION),
	linux-kernel@...r.kernel.org (open list)
Subject: Re: [PATCH v2 04/10] KVM: arm: guest debug, add stub
 KVM_SET_GUEST_DEBUG ioctl

> This commit adds a stub function to support the KVM_SET_GUEST_DEBUG
> ioctl. Currently any operation flag will return EINVAL. Actual

Well it won't return -EINVAL if you push in KVM_GUESTDBG_ENABLE or 0.

"Any unsupported flag will return -EINVAL. For now, only KVM_GUESTDBG_ENABLE is
supported, although it won't have any effects."

> functionality will be added with further patches.
> 
> Signed-off-by: Alex Bennée <alex.bennee@...aro.org>.
> 
> ---
> v2
>   - simplified form of the ioctl (stuff will go into setup_debug)
> 
> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
> index b112efc..06c5064 100644
> --- a/Documentation/virtual/kvm/api.txt
> +++ b/Documentation/virtual/kvm/api.txt
> @@ -2604,7 +2604,7 @@ handled.
>  4.87 KVM_SET_GUEST_DEBUG
> 
>  Capability: KVM_CAP_SET_GUEST_DEBUG
> -Architectures: x86, s390, ppc
> +Architectures: x86, s390, ppc, arm64
>  Type: vcpu ioctl
>  Parameters: struct kvm_guest_debug (in)
>  Returns: 0 on success; -1 on error
> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
> index 5560f74..445933d 100644
> --- a/arch/arm/kvm/arm.c
> +++ b/arch/arm/kvm/arm.c
> @@ -183,6 +183,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  	case KVM_CAP_ARM_PSCI:
>  	case KVM_CAP_ARM_PSCI_0_2:
>  	case KVM_CAP_READONLY_MEM:
> +	case KVM_CAP_SET_GUEST_DEBUG:
>  		r = 1;
>  		break;
>  	case KVM_CAP_COALESCED_MMIO:
> @@ -303,10 +304,21 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
>  	kvm_arm_set_running_vcpu(NULL);
>  }
> 
> +#define KVM_GUESTDBG_VALID (KVM_GUESTDBG_ENABLE)

That makes me rather think that it is another flag.

We(s390x) use VALID_GUESTDBG_FLAGS, what about that or KVM_GUESTDBG_VALID_MASK?

> +
>  int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
>  					struct kvm_guest_debug *dbg)
>  {
> -	return -EINVAL;
> +	if (dbg->control & KVM_GUESTDBG_ENABLE) {
> +		if (dbg->control & ~KVM_GUESTDBG_VALID)
> +			return -EINVAL;

I'd move that check directly to the start of the function and bail out on any
unsupported flag.

> +
> +		vcpu->guest_debug = dbg->control;
> +	} else {
> +		/* If not enabled clear all flags */
> +		vcpu->guest_debug = 0;
> +	}
> +	return 0;
>  }
> 
> 

David

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