linux-kernel - [PATCH v3 06/11] KVM: x86: lapic: don't allow to change APIC ID when apic acceleration is enabled

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Date:   Tue,  1 Mar 2022 20:26:34 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Zhi Wang <zhi.a.wang@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        David Airlie <airlied@...ux.ie>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        x86@...nel.org, intel-gvt-dev@...ts.freedesktop.org,
        Joerg Roedel <joro@...tes.org>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Jim Mattson <jmattson@...gle.com>,
        intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        dri-devel@...ts.freedesktop.org,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH v3 06/11] KVM: x86: lapic: don't allow to change APIC ID when apic acceleration is enabled

No normal guest has any reason to change physical APIC IDs, and
allowing this introduces bugs into APIC acceleration code.

Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/lapic.c | 28 +++++++++++++++++++++++-----
 1 file changed, 23 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 80a2020c4db40..ffb5fc6449bc5 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2042,10 +2042,20 @@ static int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
 
 	switch (reg) {
 	case APIC_ID:		/* Local APIC ID */
-		if (!apic_x2apic_mode(apic))
-			kvm_apic_set_xapic_id(apic, val >> 24);
-		else
+		if (apic_x2apic_mode(apic)) {
 			ret = 1;
+			break;
+		}
+		/*
+		 * Don't allow setting APIC ID with any APIC acceleration
+		 * enabled to avoid unexpected issues
+		 */
+		if (enable_apicv && ((val >> 24) != apic->vcpu->vcpu_id)) {
+			kvm_vm_bugged(apic->vcpu->kvm);
+			break;
+		}
+
+		kvm_apic_set_xapic_id(apic, val >> 24);
 		break;
 
 	case APIC_TASKPRI:
@@ -2613,8 +2623,16 @@ int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu)
 static int kvm_apic_state_fixup(struct kvm_vcpu *vcpu,
 		struct kvm_lapic_state *s, bool set)
 {
-	if (apic_x2apic_mode(vcpu->arch.apic)) {
-		u32 *id = (u32 *)(s->regs + APIC_ID);
+	u32 *id = (u32 *)(s->regs + APIC_ID);
+
+	if (!apic_x2apic_mode(vcpu->arch.apic)) {
+		/* Don't allow setting APIC ID with any APIC acceleration
+		 * enabled to avoid unexpected issues
+		 */
+		if (enable_apicv && (*id >> 24) != vcpu->vcpu_id)
+			return -EINVAL;
+	} else {
+
 		u32 *ldr = (u32 *)(s->regs + APIC_LDR);
 		u64 icr;
 
-- 
2.26.3