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

David Hildenbrand
2015-04-01T15:55:29Z

> 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