[PATCH v2] x86: Delay skip of emulated hypercall instruction

[Marian Rotariu <mrotariu@xxxxxxxxxxxxxxx>]

The IP increment should be done after the hypercall emulation, after
calling the various handlers. In this way, these handlers can accurately
identify the the IP of the VMCALL if they need it.

This patch also fixes the Hyper-V handler which now has the correct IP
of the VMCALL and which now uses the return code of the
kvm_skip_emulated_instruction() call.

Signed-off-by: Marian Rotariu <mrotariu@xxxxxxxxxxxxxxx>
Suggested-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
----
v1 -> v2
- extended the modifications to include the Hyper-V handler per Paolo Bonzini's
  request
---
 arch/x86/kvm/hyperv.c |  2 +-
 arch/x86/kvm/x86.c    | 19 +++++++++++--------
 2 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index dc97f25..5d13abe 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -1223,7 +1223,7 @@ static int kvm_hv_hypercall_complete_userspace(struct kvm_vcpu *vcpu)
 	struct kvm_run *run = vcpu->run;
 
 	kvm_hv_hypercall_set_result(vcpu, run->hyperv.u.hcall.result);
-	return 1;
+	return kvm_skip_emulated_instruction(vcpu);
 }
 
 int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 18b5ca7..617ad0f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6527,12 +6527,13 @@ void kvm_vcpu_deactivate_apicv(struct kvm_vcpu *vcpu)
 int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
 {
 	unsigned long nr, a0, a1, a2, a3, ret;
-	int op_64_bit, r;
+	int op_64_bit;
 
-	r = kvm_skip_emulated_instruction(vcpu);
-
-	if (kvm_hv_hypercall_enabled(vcpu->kvm))
-		return kvm_hv_hypercall(vcpu);
+	if (kvm_hv_hypercall_enabled(vcpu->kvm)) {
+		if (!kvm_hv_hypercall(vcpu))
+			return 0;
+		goto out;
+	}
 
 	nr = kvm_register_read(vcpu, VCPU_REGS_RAX);
 	a0 = kvm_register_read(vcpu, VCPU_REGS_RBX);
@@ -6553,7 +6554,7 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
 
 	if (kvm_x86_ops->get_cpl(vcpu) != 0) {
 		ret = -KVM_EPERM;
-		goto out;
+		goto out_error;
 	}
 
 	switch (nr) {
@@ -6573,12 +6574,14 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
 		ret = -KVM_ENOSYS;
 		break;
 	}
-out:
+out_error:
 	if (!op_64_bit)
 		ret = (u32)ret;
 	kvm_register_write(vcpu, VCPU_REGS_RAX, ret);
+
+out:
 	++vcpu->stat.hypercalls;
-	return r;
+	return kvm_skip_emulated_instruction(vcpu);
 }
 EXPORT_SYMBOL_GPL(kvm_emulate_hypercall);
 
-- 
2.7.4