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

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Date:	Thu, 9 Apr 2015 14:28:07 +0200
From:	Andrew Jones <drjones@...hat.com>
To:	David Hildenbrand <dahi@...ux.vnet.ibm.com>
Cc:	Alex Bennée <alex.bennee@...aro.org>,
	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,
	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>,
	"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 04/10] KVM: arm: guest debug, add stub
 KVM_SET_GUEST_DEBUG ioctl

On Wed, Apr 01, 2015 at 05:55:29PM +0200, David Hildenbrand wrote:
> > 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
>

I don't see any follow-up from Alex on this, so I feel the need to
"+1" all David's comments here.

drew
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