linux-kernel - [PATCH v19 090/130] KVM: x86: Assume timer IRQ was injected if APIC state is proteced

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Message-Id: <b557cb31b634d0bad229a43e501d587b979c2368.1708933498.git.isaku.yamahata@intel.com>
Date: Mon, 26 Feb 2024 00:26:32 -0800
From: isaku.yamahata@...el.com
To: kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: isaku.yamahata@...el.com,
	isaku.yamahata@...il.com,
	Paolo Bonzini <pbonzini@...hat.com>,
	erdemaktas@...gle.com,
	Sean Christopherson <seanjc@...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
Subject: [PATCH v19 090/130] KVM: x86: Assume timer IRQ was injected if APIC state is proteced

From: Sean Christopherson <seanjc@...gle.com>

If APIC state is protected, i.e. the vCPU is a TDX guest, assume a timer
IRQ was injected when deciding whether or not to busy wait in the "timer
advanced" path.  The "real" vIRR is not readable/writable, so trying to
query for a pending timer IRQ will return garbage.

Note, TDX can scour the PIR if it wants to be more precise and skip the
"wait" call entirely.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
---
 arch/x86/kvm/lapic.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index e8034f2f2dd1..8025c7f614e0 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1774,8 +1774,17 @@ static void apic_update_lvtt(struct kvm_lapic *apic)
 static bool lapic_timer_int_injected(struct kvm_vcpu *vcpu)
 {
 	struct kvm_lapic *apic = vcpu->arch.apic;
-	u32 reg = kvm_lapic_get_reg(apic, APIC_LVTT);
+	u32 reg;
 
+	/*
+	 * Assume a timer IRQ was "injected" if the APIC is protected.  KVM's
+	 * copy of the vIRR is bogus, it's the responsibility of the caller to
+	 * precisely check whether or not a timer IRQ is pending.
+	 */
+	if (apic->guest_apic_protected)
+		return true;
+
+	reg  = kvm_lapic_get_reg(apic, APIC_LVTT);
 	if (kvm_apic_hw_enabled(apic)) {
 		int vec = reg & APIC_VECTOR_MASK;
 		void *bitmap = apic->regs + APIC_ISR;
-- 
2.25.1