linux-kernel - Re: [PATCH 01/10] KVM: nVMX: Move reflection check into nested_vmx_reflect

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Date:   Tue, 17 Mar 2020 09:16:31 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Xiaoyao Li <xiaoyao.li@...el.com>
Subject: Re: [PATCH 01/10] KVM: nVMX: Move reflection check into
 nested_vmx_reflect_vmexit()

On Mon, Mar 16, 2020 at 10:33:27PM -0700, Sean Christopherson wrote:
> On Fri, Mar 13, 2020 at 01:12:33PM +0100, Vitaly Kuznetsov wrote:
> > Sean Christopherson <sean.j.christopherson@...el.com> writes:
> > 
> > > -static inline int nested_vmx_reflect_vmexit(struct kvm_vcpu *vcpu,
> > > -					    u32 exit_reason)
> > > +static inline bool nested_vmx_reflect_vmexit(struct kvm_vcpu *vcpu,
> > > +					     u32 exit_reason)
> > >  {
> > > -	u32 exit_intr_info = vmcs_read32(VM_EXIT_INTR_INFO);
> > > +	u32 exit_intr_info;
> > > +
> > > +	if (!nested_vmx_exit_reflected(vcpu, exit_reason))
> > > +		return false;
> > 
> > (unrelated to your patch)
> > 
> > It's probably just me but 'nested_vmx_exit_reflected()' name always
> > makes me thinkg 'the vmexit WAS [already] reflected' and not 'the vmexit
> > NEEDS to be reflected'. 'nested_vmx_exit_needs_reflecting()' maybe?
> 
> Not just you.  It'd be nice if the name some how reflected (ha) that the
> logic is mostly based on whether or not L1 expects the exit, with a few
> exceptions.  E.g. something like
> 
> 	if (!l1_expects_vmexit(...) && !is_system_vmexit(...))
> 		return false;

Doh, the system VM-Exit logic is backwards, it should be

	if (!l1_expects_vmexit(...) || is_system_vmexit(...))
		return false;
> 
> The downside of that is the logic is split, which is probably a net loss?