Hello Maxim Levitsky,
The patch 92e7d5c83aff: "KVM: x86: allow L1 to not intercept triple
fault" from Nov 3, 2022, leads to the following Smatch static checker
warning:
arch/x86/kvm/x86.c:10873 vcpu_enter_guest()
error: uninitialized symbol 'r'.
arch/x86/kvm/x86.c
10509 static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
10510 {
10511 int r;
10512 bool req_int_win =
10513 dm_request_for_irq_injection(vcpu) &&
10514 kvm_cpu_accept_dm_intr(vcpu);
10515 fastpath_t exit_fastpath;
10516
10517 bool req_immediate_exit = false;
10518
10519 if (kvm_request_pending(vcpu)) {
10520 if (kvm_check_request(KVM_REQ_VM_DEAD, vcpu)) {
10521 r = -EIO;
10522 goto out;
10523 }
10524
10525 if (kvm_dirty_ring_check_request(vcpu)) {
10526 r = 0;
10527 goto out;
10528 }
10529
10530 if (kvm_check_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu)) {
10531 if (unlikely(!kvm_x86_ops.nested_ops->get_nested_state_pages(vcpu))) {
10532 r = 0;
10533 goto out;
10534 }
10535 }
10536 if (kvm_check_request(KVM_REQ_MMU_FREE_OBSOLETE_ROOTS, vcpu))
10537 kvm_mmu_free_obsolete_roots(vcpu);
10538 if (kvm_check_request(KVM_REQ_MIGRATE_TIMER, vcpu))
10539 __kvm_migrate_timers(vcpu);
10540 if (kvm_check_request(KVM_REQ_MASTERCLOCK_UPDATE, vcpu))
10541 kvm_update_masterclock(vcpu->kvm);
10542 if (kvm_check_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu))
10543 kvm_gen_kvmclock_update(vcpu);
10544 if (kvm_check_request(KVM_REQ_CLOCK_UPDATE, vcpu)) {
10545 r = kvm_guest_time_update(vcpu);
10546 if (unlikely(r))
10547 goto out;
10548 }
10549 if (kvm_check_request(KVM_REQ_MMU_SYNC, vcpu))
10550 kvm_mmu_sync_roots(vcpu);
10551 if (kvm_check_request(KVM_REQ_LOAD_MMU_PGD, vcpu))
10552 kvm_mmu_load_pgd(vcpu);
10553 if (kvm_check_request(KVM_REQ_TLB_FLUSH, vcpu)) {
10554 kvm_vcpu_flush_tlb_all(vcpu);
10555
10556 /* Flushing all ASIDs flushes the current ASID... */
10557 kvm_clear_request(KVM_REQ_TLB_FLUSH_CURRENT, vcpu);
10558 }
10559 kvm_service_local_tlb_flush_requests(vcpu);
10560
10561 if (kvm_check_request(KVM_REQ_REPORT_TPR_ACCESS, vcpu)) {
10562 vcpu->run->exit_reason = KVM_EXIT_TPR_ACCESS;
10563 r = 0;
10564 goto out;
10565 }
10566 if (kvm_test_request(KVM_REQ_TRIPLE_FAULT, vcpu)) {
10567 if (is_guest_mode(vcpu))
10568 kvm_x86_ops.nested_ops->triple_fault(vcpu);
10569
10570 if (kvm_check_request(KVM_REQ_TRIPLE_FAULT, vcpu)) {
10571 vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;
10572 vcpu->mmio_needed = 0;
10573 r = 0;
10574 }
"r" not initialized on else path. Forgetting to set the error code is
the canonical bug for do-nothing gotos.
10575 goto out;
10576 }
10577 if (kvm_check_request(KVM_REQ_APF_HALT, vcpu)) {
10578 /* Page is swapped out. Do synthetic halt */
10579 vcpu->arch.apf.halted = true;
10580 r = 1;
10581 goto out;
10582 }
10583 if (kvm_check_request(KVM_REQ_STEAL_UPDATE, vcpu))
10584 record_steal_time(vcpu);
10585 if (kvm_check_request(KVM_REQ_SMI, vcpu))
10586 process_smi(vcpu);
10587 if (kvm_check_request(KVM_REQ_NMI, vcpu))
10588 process_nmi(vcpu);
10589 if (kvm_check_request(KVM_REQ_PMU, vcpu))
10590 kvm_pmu_handle_event(vcpu);
10591 if (kvm_check_request(KVM_REQ_PMI, vcpu))
10592 kvm_pmu_deliver_pmi(vcpu);
10593 if (kvm_check_request(KVM_REQ_IOAPIC_EOI_EXIT, vcpu)) {
10594 BUG_ON(vcpu->arch.pending_ioapic_eoi > 255);
10595 if (test_bit(vcpu->arch.pending_ioapic_eoi,
10596 vcpu->arch.ioapic_handled_vectors)) {
10597 vcpu->run->exit_reason = KVM_EXIT_IOAPIC_EOI;
10598 vcpu->run->eoi.vector =
10599 vcpu->arch.pending_ioapic_eoi;
10600 r = 0;
10601 goto out;
10602 }
10603 }
10604 if (kvm_check_request(KVM_REQ_SCAN_IOAPIC, vcpu))
10605 vcpu_scan_ioapic(vcpu);
10606 if (kvm_check_request(KVM_REQ_LOAD_EOI_EXITMAP, vcpu))
10607 vcpu_load_eoi_exitmap(vcpu);
10608 if (kvm_check_request(KVM_REQ_APIC_PAGE_RELOAD, vcpu))
10609 kvm_vcpu_reload_apic_access_page(vcpu);
10610 if (kvm_check_request(KVM_REQ_HV_CRASH, vcpu)) {
10611 vcpu->run->exit_reason = KVM_EXIT_SYSTEM_EVENT;
10612 vcpu->run->system_event.type = KVM_SYSTEM_EVENT_CRASH;
10613 vcpu->run->system_event.ndata = 0;
10614 r = 0;
10615 goto out;
10616 }
10617 if (kvm_check_request(KVM_REQ_HV_RESET, vcpu)) {
10618 vcpu->run->exit_reason = KVM_EXIT_SYSTEM_EVENT;
10619 vcpu->run->system_event.type = KVM_SYSTEM_EVENT_RESET;
10620 vcpu->run->system_event.ndata = 0;
10621 r = 0;
10622 goto out;
10623 }
10624 if (kvm_check_request(KVM_REQ_HV_EXIT, vcpu)) {
10625 struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
10626
10627 vcpu->run->exit_reason = KVM_EXIT_HYPERV;
10628 vcpu->run->hyperv = hv_vcpu->exit;
10629 r = 0;
10630 goto out;
10631 }
10632
10633 /*
10634 * KVM_REQ_HV_STIMER has to be processed after
10635 * KVM_REQ_CLOCK_UPDATE, because Hyper-V SynIC timers
10636 * depend on the guest clock being up-to-date
10637 */
10638 if (kvm_check_request(KVM_REQ_HV_STIMER, vcpu))
10639 kvm_hv_process_stimers(vcpu);
10640 if (kvm_check_request(KVM_REQ_APICV_UPDATE, vcpu))
10641 kvm_vcpu_update_apicv(vcpu);
10642 if (kvm_check_request(KVM_REQ_APF_READY, vcpu))
10643 kvm_check_async_pf_completion(vcpu);
10644 if (kvm_check_request(KVM_REQ_MSR_FILTER_CHANGED, vcpu))
10645 static_call(kvm_x86_msr_filter_changed)(vcpu);
10646
10647 if (kvm_check_request(KVM_REQ_UPDATE_CPU_DIRTY_LOGGING, vcpu))
10648 static_call(kvm_x86_update_cpu_dirty_logging)(vcpu);
10649 }
10650
10651 if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win ||
10652 kvm_xen_has_interrupt(vcpu)) {
10653 ++vcpu->stat.req_event;
10654 r = kvm_apic_accept_events(vcpu);
10655 if (r < 0) {
10656 r = 0;
10657 goto out;
10658 }
10659 if (vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED) {
10660 r = 1;
10661 goto out;
10662 }
10663
10664 r = kvm_check_and_inject_events(vcpu, &req_immediate_exit);
10665 if (r < 0) {
10666 r = 0;
10667 goto out;
10668 }
10669 if (req_int_win)
10670 static_call(kvm_x86_enable_irq_window)(vcpu);
10671
10672 if (kvm_lapic_enabled(vcpu)) {
10673 update_cr8_intercept(vcpu);
10674 kvm_lapic_sync_to_vapic(vcpu);
10675 }
10676 }
10677
10678 r = kvm_mmu_reload(vcpu);
10679 if (unlikely(r)) {
10680 goto cancel_injection;
10681 }
10682
10683 preempt_disable();
10684
10685 static_call(kvm_x86_prepare_switch_to_guest)(vcpu);
10686
10687 /*
10688 * Disable IRQs before setting IN_GUEST_MODE. Posted interrupt
10689 * IPI are then delayed after guest entry, which ensures that they
10690 * result in virtual interrupt delivery.
10691 */
10692 local_irq_disable();
10693
10694 /* Store vcpu->apicv_active before vcpu->mode. */
10695 smp_store_release(&vcpu->mode, IN_GUEST_MODE);
10696
10697 kvm_vcpu_srcu_read_unlock(vcpu);
10698
10699 /*
10700 * 1) We should set ->mode before checking ->requests. Please see
10701 * the comment in kvm_vcpu_exiting_guest_mode().
10702 *
10703 * 2) For APICv, we should set ->mode before checking PID.ON. This
10704 * pairs with the memory barrier implicit in pi_test_and_set_on
10705 * (see vmx_deliver_posted_interrupt).
10706 *
10707 * 3) This also orders the write to mode from any reads to the page
10708 * tables done while the VCPU is running. Please see the comment
10709 * in kvm_flush_remote_tlbs.
10710 */
10711 smp_mb__after_srcu_read_unlock();
10712
10713 /*
10714 * Process pending posted interrupts to handle the case where the
10715 * notification IRQ arrived in the host, or was never sent (because the
10716 * target vCPU wasn't running). Do this regardless of the vCPU's APICv
10717 * status, KVM doesn't update assigned devices when APICv is inhibited,
10718 * i.e. they can post interrupts even if APICv is temporarily disabled.
10719 */
10720 if (kvm_lapic_enabled(vcpu))
10721 static_call_cond(kvm_x86_sync_pir_to_irr)(vcpu);
10722
10723 if (kvm_vcpu_exit_request(vcpu)) {
10724 vcpu->mode = OUTSIDE_GUEST_MODE;
10725 smp_wmb();
10726 local_irq_enable();
10727 preempt_enable();
10728 kvm_vcpu_srcu_read_lock(vcpu);
10729 r = 1;
10730 goto cancel_injection;
10731 }
10732
10733 if (req_immediate_exit) {
10734 kvm_make_request(KVM_REQ_EVENT, vcpu);
10735 static_call(kvm_x86_request_immediate_exit)(vcpu);
10736 }
10737
10738 fpregs_assert_state_consistent();
10739 if (test_thread_flag(TIF_NEED_FPU_LOAD))
10740 switch_fpu_return();
10741
10742 if (vcpu->arch.guest_fpu.xfd_err)
10743 wrmsrl(MSR_IA32_XFD_ERR, vcpu->arch.guest_fpu.xfd_err);
10744
10745 if (unlikely(vcpu->arch.switch_db_regs)) {
10746 set_debugreg(0, 7);
10747 set_debugreg(vcpu->arch.eff_db[0], 0);
10748 set_debugreg(vcpu->arch.eff_db[1], 1);
10749 set_debugreg(vcpu->arch.eff_db[2], 2);
10750 set_debugreg(vcpu->arch.eff_db[3], 3);
10751 } else if (unlikely(hw_breakpoint_active())) {
10752 set_debugreg(0, 7);
10753 }
10754
10755 guest_timing_enter_irqoff();
10756
10757 for (;;) {
10758 /*
10759 * Assert that vCPU vs. VM APICv state is consistent. An APICv
10760 * update must kick and wait for all vCPUs before toggling the
10761 * per-VM state, and responsing vCPUs must wait for the update
10762 * to complete before servicing KVM_REQ_APICV_UPDATE.
10763 */
10764 WARN_ON_ONCE((kvm_vcpu_apicv_activated(vcpu) != kvm_vcpu_apicv_active(vcpu)) &&
10765 (kvm_get_apic_mode(vcpu) != LAPIC_MODE_DISABLED));
10766
10767 exit_fastpath = static_call(kvm_x86_vcpu_run)(vcpu);
10768 if (likely(exit_fastpath != EXIT_FASTPATH_REENTER_GUEST))
10769 break;
10770
10771 if (kvm_lapic_enabled(vcpu))
10772 static_call_cond(kvm_x86_sync_pir_to_irr)(vcpu);
10773
10774 if (unlikely(kvm_vcpu_exit_request(vcpu))) {
10775 exit_fastpath = EXIT_FASTPATH_EXIT_HANDLED;
10776 break;
10777 }
10778 }
10779
10780 /*
10781 * Do this here before restoring debug registers on the host. And
10782 * since we do this before handling the vmexit, a DR access vmexit
10783 * can (a) read the correct value of the debug registers, (b) set
10784 * KVM_DEBUGREG_WONT_EXIT again.
10785 */
10786 if (unlikely(vcpu->arch.switch_db_regs & KVM_DEBUGREG_WONT_EXIT)) {
10787 WARN_ON(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP);
10788 static_call(kvm_x86_sync_dirty_debug_regs)(vcpu);
10789 kvm_update_dr0123(vcpu);
10790 kvm_update_dr7(vcpu);
10791 }
10792
10793 /*
10794 * If the guest has used debug registers, at least dr7
10795 * will be disabled while returning to the host.
10796 * If we don't have active breakpoints in the host, we don't
10797 * care about the messed up debug address registers. But if
10798 * we have some of them active, restore the old state.
10799 */
10800 if (hw_breakpoint_active())
10801 hw_breakpoint_restore();
10802
10803 vcpu->arch.last_vmentry_cpu = vcpu->cpu;
10804 vcpu->arch.last_guest_tsc = kvm_read_l1_tsc(vcpu, rdtsc());
10805
10806 vcpu->mode = OUTSIDE_GUEST_MODE;
10807 smp_wmb();
10808
10809 /*
10810 * Sync xfd before calling handle_exit_irqoff() which may
10811 * rely on the fact that guest_fpu::xfd is up-to-date (e.g.
10812 * in #NM irqoff handler).
10813 */
10814 if (vcpu->arch.xfd_no_write_intercept)
10815 fpu_sync_guest_vmexit_xfd_state();
10816
10817 static_call(kvm_x86_handle_exit_irqoff)(vcpu);
10818
10819 if (vcpu->arch.guest_fpu.xfd_err)
10820 wrmsrl(MSR_IA32_XFD_ERR, 0);
10821
10822 /*
10823 * Consume any pending interrupts, including the possible source of
10824 * VM-Exit on SVM and any ticks that occur between VM-Exit and now.
10825 * An instruction is required after local_irq_enable() to fully unblock
10826 * interrupts on processors that implement an interrupt shadow, the
10827 * stat.exits increment will do nicely.
10828 */
10829 kvm_before_interrupt(vcpu, KVM_HANDLING_IRQ);
10830 local_irq_enable();
10831 ++vcpu->stat.exits;
10832 local_irq_disable();
10833 kvm_after_interrupt(vcpu);
10834
10835 /*
10836 * Wait until after servicing IRQs to account guest time so that any
10837 * ticks that occurred while running the guest are properly accounted
10838 * to the guest. Waiting until IRQs are enabled degrades the accuracy
10839 * of accounting via context tracking, but the loss of accuracy is
10840 * acceptable for all known use cases.
10841 */
10842 guest_timing_exit_irqoff();
10843
10844 local_irq_enable();
10845 preempt_enable();
10846
10847 kvm_vcpu_srcu_read_lock(vcpu);
10848
10849 /*
10850 * Profile KVM exit RIPs:
10851 */
10852 if (unlikely(prof_on == KVM_PROFILING)) {
10853 unsigned long rip = kvm_rip_read(vcpu);
10854 profile_hit(KVM_PROFILING, (void *)rip);
10855 }
10856
10857 if (unlikely(vcpu->arch.tsc_always_catchup))
10858 kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
10859
10860 if (vcpu->arch.apic_attention)
10861 kvm_lapic_sync_from_vapic(vcpu);
10862
10863 r = static_call(kvm_x86_handle_exit)(vcpu, exit_fastpath);
10864 return r;
10865
10866 cancel_injection:
10867 if (req_immediate_exit)
10868 kvm_make_request(KVM_REQ_EVENT, vcpu);
10869 static_call(kvm_x86_cancel_injection)(vcpu);
10870 if (unlikely(vcpu->arch.apic_attention))
10871 kvm_lapic_sync_from_vapic(vcpu);
10872 out:
--> 10873 return r;
10874 }
regards,
dan carpenter
