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

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Message-ID: <8738491j1g.fsf@linaro.org>
Date:	Thu, 09 Apr 2015 15:19:07 +0100
From:	Alex Bennée <alex.bennee@...aro.org>
To:	Andrew Jones <drjones@...hat.com>
Cc:	David Hildenbrand <dahi@...ux.vnet.ibm.com>, 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


Andrew Jones <drjones@...hat.com> writes:

> 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.

Yeah they make sense. Will do.

-- 
Alex Bennée
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