From c4a365cd4a4ec105012ab3ae5ff5cf11f8533771 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Thu, 22 Jan 2026 18:28:16 -0800 Subject: [PATCH] KVM: x86: Drop WARN on INIT/SIPI being blocked when vCPU is in Wait-For-SIPI Drop the sanity check in kvm_apic_accept_events() that attempts to detect KVM bugs by asserting that a vCPU isn't in Wait-For-SIPI if INIT/SIPI are blocked, because if INIT is blocked, then it should be impossible for a vCPU to get into WFS in the first place. Unfortunately, syzbot is smarter than KVM (and its maintainers), and circumvented the guards put in place by commit 0fe3e8d804fd ("KVM: x86: Move INIT_RECEIVED vs. INIT/SIPI blocked check to KVM_RUN") by swapping the order and stuffing VMXON after INIT, and then triggering kvm_apic_accept_events() by way of KVM_GET_MP_STATE. Simply drop the WARN as it hasn't detected any meaningful KVM bugs in years (if ever?), and preventing userspace from clobbering guest state is generally a non-goal. More importantly, fully closing the hole would likely require enforcing some amount of ordering in KVM's ioctls, which is a much bigger risk than simply deleting the WARN. Reported-by: syzbot+59f2c3a3fc4f6c09b8cd@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/6925da1b.a70a0220.d98e3.00b0.GAE@google.com Link: https://patch.msgid.link/20260123022816.2283567-1-seanjc@google.com Signed-off-by: Sean Christopherson --- arch/x86/kvm/lapic.c | 1 - 1 file changed, 1 deletion(-) diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index 1597dd0b0cc66..01c2557bfa055 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -3498,7 +3498,6 @@ int kvm_apic_accept_events(struct kvm_vcpu *vcpu) * wait-for-SIPI (WFS). */ if (!kvm_apic_init_sipi_allowed(vcpu)) { - WARN_ON_ONCE(vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED); clear_bit(KVM_APIC_SIPI, &apic->pending_events); return 0; } -- 2.47.3