Re: [PATCH v2 04/10] KVM: arm: guest debug, add stub KVM_SET_GUEST_DEBUG ioctl

Andrew Jones
2015-04-09T12:21:06Z

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@linaro.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