Re: [PATCH v6 5/7] KVM: nVMX: Set VM-{Fail,Exit} failure info via params, not return val

[Paolo Bonzini <pbonzini@redhat.com>]

On 11/04/19 21:18, Sean Christopherson wrote:
> Convert all top-level nested VM-Enter consistency check functions to
> use explicit parameters to pass failure information to the caller.
> Using an explicit parameter achieves several goals:
> 
>   - Provides consistent prototypes for all functions.
>   - Self-documents the net effect of failure, e.g. without the explicit
>     parameter it may not be obvious that nested_vmx_check_guest_state()
>     leads to a VM-Exit.
>   - Does not give the false impression that failure information is
>     always consumed and/or relevant, e.g. vmx_set_nested_state() only
>     cares whether or not the checks were successful.
> 
> Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---

I think we have to agree to disagree on this one. :)

I'd rather have something like this (untested) replacing patches 5 and 6:

-------------- 8< -----------------
From: Paolo Bonzini <pbonzini@redhat.com>
Subject: [PATCH] KVM: nVMX: Return -EINVAL when signaling failure in pre-VM-Entry helpers
    
Convert all top-level nested VM-Enter consistency check functions to
return 0/-EINVAL instead of failure codes, since now they can only
ever return one failure code.

This also does not give the false impression that failure information is
always consumed and/or relevant, e.g. vmx_set_nested_state() only
cares whether or not the checks were successful.

nested_check_host_control_regs() can also now be inlined into its caller,
nested_vmx_check_host_state, since the two have effectively become the
same function.

Based on a patch by Sean Christopherson.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index f58de538e6d3..c75edccdd3bc 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -2595,16 +2595,13 @@ static int nested_vmx_check_controls(struct kvm_vcpu *vcpu,
 	if (nested_check_vm_execution_controls(vcpu, vmcs12) ||
 	    nested_check_vm_exit_controls(vcpu, vmcs12) ||
 	    nested_check_vm_entry_controls(vcpu, vmcs12))
-		return VMXERR_ENTRY_INVALID_CONTROL_FIELD;
+		return -EINVAL;
 
 	return 0;
 }
 
-/*
- * Checks related to Host Control Registers and MSRs
- */
-static int nested_check_host_control_regs(struct kvm_vcpu *vcpu,
-                                          struct vmcs12 *vmcs12)
+static int nested_vmx_check_host_state(struct kvm_vcpu *vcpu,
+				       struct vmcs12 *vmcs12)
 {
 	bool ia32e;
 
@@ -2639,15 +2636,6 @@ static int nested_check_host_control_regs(struct kvm_vcpu *vcpu,
 	return 0;
 }
 
-static int nested_vmx_check_host_state(struct kvm_vcpu *vcpu,
-				       struct vmcs12 *vmcs12)
-{
-	if (nested_check_host_control_regs(vcpu, vmcs12))
-		return VMXERR_ENTRY_INVALID_HOST_STATE_FIELD;
-
-	return 0;
-}
-
 static int nested_vmx_check_vmcs_link_ptr(struct kvm_vcpu *vcpu,
 					  struct vmcs12 *vmcs12)
 {
@@ -3152,13 +3140,11 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
 			launch ? VMXERR_VMLAUNCH_NONCLEAR_VMCS
 			       : VMXERR_VMRESUME_NONLAUNCHED_VMCS);
 
-	ret = nested_vmx_check_controls(vcpu, vmcs12);
-	if (ret)
-		return nested_vmx_failValid(vcpu, ret);
+	if (nested_vmx_check_controls(vcpu, vmcs12))
+		return nested_vmx_failValid(vcpu, VMXERR_ENTRY_INVALID_CONTROL_FIELD);
 
-	ret = nested_vmx_check_host_state(vcpu, vmcs12);
-	if (ret)
-		return nested_vmx_failValid(vcpu, ret);
+	if (nested_vmx_check_host_state(vcpu, vmcs12))
+		return nested_vmx_failValid(vcpu, VMXERR_ENTRY_INVALID_HOST_STATE_FIELD);
 
 	/*
 	 * We're finally done with prerequisite checking, and can start with