Liran Alon <liran.alon@xxxxxxxxxx> writes: >> On 26 Mar 2019, at 15:48, Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> wrote: >> >> Liran Alon <liran.alon@xxxxxxxxxx> writes: >> >>>> On 26 Mar 2019, at 15:07, Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> wrote: >>>> - Instread of putting the temporary HF_SMM_MASK drop to >>>> rsm_enter_protected_mode() (as was suggested by Liran), move it to >>>> emulator_set_cr() modifying its interface. emulate.c seems to be >>>> vcpu-specifics-free at this moment, we may want to keep it this way. >>>> - It seems that Hyper-V+UEFI on KVM is still broken, I'm observing sporadic >>>> hangs even with this patch. These hangs, however, seem to be unrelated to >>>> rsm. >>> >>> Feel free to share details on these hangs ;) >>> >> >> You've asked for it) >> >> The immediate issue I'm observing is some sort of a lockup which is easy >> to trigger with e.g. "-usb -device usb-tablet" on Qemu command line; it >> seems we get too many interrupts and combined with preemtion timer for >> L2 we're not making any progress: >> >> kvm_userspace_exit: reason KVM_EXIT_IOAPIC_EOI (26) >> kvm_set_irq: gsi 18 level 1 source 0 >> kvm_msi_set_irq: dst 0 vec 177 (Fixed|physical|level) >> kvm_apic_accept_irq: apicid 0 vec 177 (Fixed|edge) >> kvm_fpu: load >> kvm_entry: vcpu 0 >> kvm_exit: reason VMRESUME rip 0xfffff80000848115 info 0 0 >> kvm_entry: vcpu 0 >> kvm_exit: reason PREEMPTION_TIMER rip 0xfffff800f4448e01 info 0 0 >> kvm_nested_vmexit: rip fffff800f4448e01 reason PREEMPTION_TIMER info1 0 info2 0 int_info 0 int_info_err 0 >> kvm_nested_vmexit_inject: reason EXTERNAL_INTERRUPT info1 0 info2 0 int_info 800000b1 int_info_err 0 >> kvm_entry: vcpu 0 >> kvm_exit: reason APIC_ACCESS rip 0xfffff8000081fe11 info 10b0 0 >> kvm_apic: apic_write APIC_EOI = 0x0 >> kvm_eoi: apicid 0 vector 177 >> kvm_fpu: unload >> kvm_userspace_exit: reason KVM_EXIT_IOAPIC_EOI (26) >> ... >> (and the pattern repeats) >> >> Maybe it is a usb-only/Qemu-only problem, maybe not. >> >> -- >> Vitaly > > The trace of kvm_apic_accept_irq should indicate that __apic_accept_irq() was called to inject an interrupt to L1 guest. > (I know that now we are running in L1 because next exit is a VMRESUME). > > However, it is surprising to see that on next entry to guest, no interrupt was injected by vmx_inject_irq(). > It may be because L1 guest is currently running with interrupt disabled and therefore only an IRQ-window was requested. > (Too bad we don’t have a trace for this…) > > Next, we got an exit from L1 guest on VMRESUME. As part of it’s handling, active VMCS was changed from vmcs01 to vmcs02. > I believe the immediate exit later on preemption-timer was because the immediate-exit-request mechanism was invoked > which is now implemented by setting a VMX preemption-timer with value of 0 (Thanks to Sean). > (See vmx_vcpu_run() -> vmx_update_hv_timer() -> vmx_arm_hv_timer(vmx, 0)). > (Note that the pending interrupt was evaluated because of a recent patch of mine to nested_vmx_enter_non_root_mode() > to request KVM_REQ_EVENT when vmcs01 have requested an IRQ-window) > > Therefore when entering L2, you immediately get an exit on PREEMPTION_TIMER which will cause eventually L0 to call > vmx_check_nested_events() which notices now the pending interrupt that should have been injected before to L1 > and now exit from L2 to L1 on EXTERNAL_INTERRUPT on vector 0xb1. > > Then L1 handles the interrupt by performing an EOI to LAPIC which propagate an EOI to IOAPIC which immediately re-inject > the interrupt (after clearing the remote_irr) as the irq-line is still set. i.e. QEMU’s ioapic_eoi_broadcast() calls ioapic_service() immediate after it clears remote-irr for this pin. > > Also note that in trace we see only a single kvm_set_irq to level 1 but we don’t see immediately another kvm_set_irq to level 0. > This should indicate that in QEMU’s IOAPIC redirection-table, this pin is configured as level-triggered interrupt. > However, the trace of kvm_apic_accept_irq indicates that this interrupt is raised as an edge-triggered interrupt. > > To sum up: > 1) I would create a patch to add a trace to vcpu_enter_guest() when calling enable_smi_window() / enable_nmi_window() / enable_irq_window(). > 2) It is worth investigating why MSI trigger-mode is edge-triggered instead of level-triggered. > 3) If this is indeed a level-triggered interrupt, it is worth investigating how the interrupt source behaves. i.e. What cause this device to lower the irq-line? > (As we don’t see any I/O Port or MMIO access by L1 guest interrupt-handler before performing the EOI) > 4) Does this issue reproduce also when running with kernel-irqchip? (Instead of split-irqchip) > Thank you Liran, all are valuable suggestions. It seems the isssue doesn't reproduce with 'kernel-irqchip=on' but reproduces with "kernel-irqchip=split". My first guess would then be that we're less picky with in-kernel implementation about the observed edge/level discrepancy. I'll be investigating and share my findings. -- Vitaly
