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

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Message-ID: <ZhIX7K0WK+gYtcan@chao-email>
Date: Sun, 7 Apr 2024 11:50:04 +0800
From: Chao Gao <chao.gao@...el.com>
To: Isaku Yamahata <isaku.yamahata@...el.com>
CC: 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

>> > >+	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.

Probably it is a minor thing; if no one else thinks it is better to move the
"interrupt allowed" check to tdx_interrupt_allowed(), I am also fine with not
doing that.