linux-kernel - [PATCH v17 074/116] KVM: x86: Assume timer IRQ was injected if APIC state is proteced

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Message-Id: <bfd5a29454693f2fc95b69a741d3f836682e49f8.1699368322.git.isaku.yamahata@intel.com>
Date:   Tue,  7 Nov 2023 06:56:40 -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>,
        David Matlack <dmatlack@...gle.com>,
        Kai Huang <kai.huang@...el.com>,
        Zhi Wang <zhi.wang.linux@...il.com>, chen.bo@...el.com,
        hang.yuan@...el.com, tina.zhang@...el.com
Subject: [PATCH v17 074/116] 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>
---
 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 2aaba86ad268..35942cfee8fb 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1775,8 +1775,17 @@ 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