linux-kernel - Re: [PATCH v19 108/130] KVM: TDX: Handle TDX PV HLT hypercall

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Date: Mon, 8 Apr 2024 11:56:13 -0700
From: Isaku Yamahata <isaku.yamahata@...el.com>
To: Chao Gao <chao.gao@...el.com>
Cc: Isaku Yamahata <isaku.yamahata@...el.com>,
	Sean Christopherson <seanjc@...gle.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
	Paolo Bonzini <pbonzini@...hat.com>, erdemaktas@...gle.com,
	Sagi Shahar <sagis@...gle.com>, Kai Huang <kai.huang@...el.com>,
	chen.bo@...el.com, hang.yuan@...el.com, tina.zhang@...el.com,
	isaku.yamahata@...ux.intel.com
Subject: Re: [PATCH v19 108/130] KVM: TDX: Handle TDX PV HLT hypercall

On Sun, Apr 07, 2024 at 11:50:04AM +0800,
Chao Gao <chao.gao@...el.com> wrote:

> >> > >+	union tdx_vcpu_state_details details;
> >> > >+	struct vcpu_tdx *tdx = to_tdx(vcpu);
> >> > >+
> >> > >+	if (ret || vcpu->arch.mp_state != KVM_MP_STATE_HALTED)
> >> > >+		return true;
> >> > 
> >> > Question: why mp_state matters here?
> >> > >+
> >> > >+	if (tdx->interrupt_disabled_hlt)
> >> > >+		return false;
> >> > 
> >> > Shouldn't we move this into vt_interrupt_allowed()? VMX calls the function to
> >> > check if interrupt is disabled.
> >
> >Chao, are you suggesting to implement tdx_interrupt_allowed() as
> >"EXIT_REASON_HLT && a0" instead of "return true"?
> >I don't think it makes sense because it's rare case and we can't avoid spurious
> >wakeup for TDX case.
> 
> Yes. KVM differeniates "interrupt allowed" from "has interrupt", e.g.,
> 
> static inline bool kvm_vcpu_has_events(struct kvm_vcpu *vcpu)
> ...
> 
> 	if (kvm_arch_interrupt_allowed(vcpu) &&
> 	    (kvm_cpu_has_interrupt(vcpu) ||
> 	    kvm_guest_apic_has_interrupt(vcpu)))
> 		return true;
> 
> 
> I think tdx_protected_apic_has_interrupt() mixes them together, which isn't
> good.

Your point is code clarity.  Ok, we can code in that way. I don't expect any
performance difference.
-- 
Isaku Yamahata <isaku.yamahata@...el.com>