[PATCH 13/15] KVM: Add support for enabling capabilities per-vcpu

[Alexander Graf <agraf-l3A5Bk7waGM@public.gmane.org>]

Some times we don't want all capabilities to be available to all
our vcpus. One example for that is the OSI interface, implemented
in the next patch.

In order to have a generic mechanism in how to enable capabilities
individually, this patch introduces a new ioctl that can be used
for this purpose. That way features we don't want in all guests or
userspace configurations can just not be enabled and we're good.

Signed-off-by: Alexander Graf <agraf-l3A5Bk7waGM@public.gmane.org>

---

v1 -> v2:

  - Add flags to enable_cap
  - Update documentation for kvm_enable_cap
---
 Documentation/kvm/api.txt  |   15 +++++++++++++++
 arch/powerpc/kvm/powerpc.c |   26 ++++++++++++++++++++++++++
 include/linux/kvm.h        |   11 +++++++++++
 3 files changed, 52 insertions(+), 0 deletions(-)

diff --git a/Documentation/kvm/api.txt b/Documentation/kvm/api.txt
index d170cb4..6a19ab6 100644
--- a/Documentation/kvm/api.txt
+++ b/Documentation/kvm/api.txt
@@ -749,6 +749,21 @@ Writes debug registers into the vcpu.
 See KVM_GET_DEBUGREGS for the data structure. The flags field is unused
 yet and must be cleared on entry.
 
+4.34 KVM_ENABLE_CAP
+
+Capability: basic
+Architectures: all
+Type: vcpu ioctl
+Parameters: struct kvm_enable_cap (in)
+Returns: 0 on success; -1 on error
+
+Not all extensions are enabled by default. Using this ioctl the application
+can enable an extension, making it available to the guest.
+
+On systems that do not support this ioctl, it always fails. On systems that
+do support it, it only works for extensions that are supported for enablement.
+As of writing this the only enablement enabled extenion is KVM_CAP_PPC_OSI.
+
 
 5. The kvm_run structure
 
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index a28a512..8bd8204 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -462,6 +462,23 @@ int kvm_vcpu_ioctl_interrupt(struct kvm_vcpu *vcpu, struct kvm_interrupt *irq)
 	return 0;
 }
 
+static int kvm_vcpu_ioctl_enable_cap(struct kvm_vcpu *vcpu,
+				     struct kvm_enable_cap *cap)
+{
+	int r;
+
+	if (cap->flags)
+		return -EINVAL;
+
+	switch (cap->cap) {
+	default:
+		r = -EINVAL;
+		break;
+	}
+
+	return r;
+}
+
 int kvm_arch_vcpu_ioctl_get_mpstate(struct kvm_vcpu *vcpu,
                                     struct kvm_mp_state *mp_state)
 {
@@ -490,6 +507,15 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 		r = kvm_vcpu_ioctl_interrupt(vcpu, &irq);
 		break;
 	}
+	case KVM_ENABLE_CAP:
+	{
+		struct kvm_enable_cap cap;
+		r = -EFAULT;
+		if (copy_from_user(&cap, argp, sizeof(cap)))
+			goto out;
+		r = kvm_vcpu_ioctl_enable_cap(vcpu, &cap);
+		break;
+	}
 	default:
 		r = -EINVAL;
 	}
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index ce28767..a18ac92 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -400,6 +400,15 @@ struct kvm_ioeventfd {
 	__u8  pad[36];
 };
 
+/* for KVM_ENABLE_CAP */
+struct kvm_enable_cap {
+	/* in */
+	__u32 cap;
+	__u32 flags;
+	__u64 args[4];
+	__u8  pad[64];
+};
+
 #define KVMIO 0xAE
 
 /*
@@ -696,6 +705,8 @@ struct kvm_clock_data {
 /* Available with KVM_CAP_DEBUGREGS */
 #define KVM_GET_DEBUGREGS         _IOR(KVMIO,  0xa1, struct kvm_debugregs)
 #define KVM_SET_DEBUGREGS         _IOW(KVMIO,  0xa2, struct kvm_debugregs)
+/* No need for CAP, because then it just always fails */
+#define KVM_ENABLE_CAP            _IOW(KVMIO,  0xa3, struct kvm_enable_cap)
 
 #define KVM_DEV_ASSIGN_ENABLE_IOMMU	(1 << 0)
 
-- 
1.6.0.2