Commit e6b5d16b authored Jan 09, 2024 by Sean Christopherson

KVM: VMX: Re-enter guest in fastpath for "spurious" preemption timer exits

Re-enter the guest in the fast path if VMX preeemption timer VM-Exit was
"spurious", i.e. if KVM "soft disabled" the timer by writing -1u and by
some miracle the timer expired before any other VM-Exit occurred. This is
just an intermediate step to cleaning up the preemption timer handling,
optimizing these types of spurious VM-Exits is not interesting as they are
extremely rare/infrequent.

Link: https://lore.kernel.org/r/20240110012705.506918-3-seanjc@google.com

Signed-off-by: Sean Christopherson <seanjc@google.com>

parent 9c9025ea

arch/x86/kvm/vmx/vmx.c

+9 −2

Original line number	Diff line number	Diff line
		@@ -5992,8 +5992,15 @@ static fastpath_t handle_fastpath_preemption_timer(struct kvm_vcpu *vcpu)
		{
		struct vcpu_vmx *vmx = to_vmx(vcpu);

		if (!vmx->req_immediate_exit &&
		!unlikely(vmx->loaded_vmcs->hv_timer_soft_disabled)) {
		/*
		* In the extremely unlikely scenario that this is a spurious VM-Exit
		* due to the timer expiring while it was "soft" disabled, just eat the
		* exit and re-enter the guest.
		*/
		if (unlikely(vmx->loaded_vmcs->hv_timer_soft_disabled))
		return EXIT_FASTPATH_REENTER_GUEST;

		if (!vmx->req_immediate_exit) {
		kvm_lapic_expired_hv_timer(vcpu);
		return EXIT_FASTPATH_REENTER_GUEST;
		}