2016-09-14 3:01 GMT+08:00 Radim Krcmar <rkrcmar@xxxxxxxxxx>: > 2016-09-13 19:06+0800, Wanpeng Li: >> Add -kernel_irqchip=split >> ./x86-run x86/eventinj.flat >> >> qemu-system-x86_64 -enable-kvm -machine kernel_irqchip=split -cpu host >> -device pc-testdev -device isa-debug-exit,iobase=0xf4,iosize=0x4 -vnc >> none -serial stdio -device pci-testdev -kernel x86/eventinj.flat >> enabling apic >> paging enabled >> cr0 = 80010011 >> cr3 = 7fff000 >> cr4 = 20 >> Sending vec 33 and 62 and mask one with TPR >> irq1 running >> irq1 running >> After 33/62 TPR test >> FAIL: TPR >> irq0 running >> irq0 running >> >> Both irq1 and irq0 are executing twice. >> >> qemu-system-x86-22794 [001] d..2 34591.708476: kvm_entry: vcpu 0 >> qemu-system-x86-22794 [001] ...1 34591.708478: kvm_exit: reason >> MSR_WRITE rip 0x401f33 info 0 0 >> qemu-system-x86-22794 [001] ...1 34591.708478: kvm_apic: apic_write >> APIC_EOI = 0x0 >> qemu-system-x86-22794 [001] ...1 34591.708479: kvm_eoi: apicid 0 vector 62 >> qemu-system-x86-22794 [001] ...1 34591.708479: kvm_msr: msr_write 80b = 0x0 >> qemu-system-x86-22794 [001] d..2 34591.708480: kvm_entry: vcpu 0 >> qemu-system-x86-22794 [001] ...1 34591.708482: kvm_exit: reason >> PENDING_INTERRUPT rip 0x401f35 info 0 0 >> qemu-system-x86-22794 [001] ...1 34591.708482: kvm_userspace_exit: >> reason KVM_EXIT_IRQ_WINDOW_OPEN (7) >> qemu-system-x86-22794 [001] ...1 34591.708491: kvm_inj_virq: irq 62 >> qemu-system-x86-22794 [001] d..2 34591.708492: kvm_entry: vcpu 0 >> qemu-system-x86-22794 [001] ...1 34591.708493: kvm_exit: reason >> IO_INSTRUCTION rip 0x4016ec info 3fd0008 0 >> >> From the trace we can see there is an interrupt window exit after the >> first interrupt EOI(irq 62), and the same irq(62) is injected >> duplicately after the interrupt window. >> >> The bug can disappear if kernel_irqchip is on or -x2apic, the virtual >> x2apic mode will not be set due to commit (8d14695f9542 x86, apicv: >> add virtual x2apic support), so that tpr shadow in the x2apic doesn't >> work and wrmsr TPR register will trigger vmexit, and then kvmvapic >> will be used to optimize flexpriority=N or AMD. The >> report_trp_access() which is called in kvm_lapic_reg_write() will >> trigger a userspace exit. >> >> TPR report access callbacks in qemu, kvm_handle_tpr_access() -> >> apic_handle_tpr_access_report() -> vapic_report_tpr_access() -> >> cpu_synchronize_state() will get apic register states from kvm. >> >> Later, kvm_arch_pre_run -> cpu_get_pic_interrupt(if there is a pic >> interrupt) -> apic_get_interrupt, it is a pic interrupt, however it >> gets the stale irq from apic register sync by report tpr access and >> KVM_INTERRUPT the second duplicate interrupt. >> >> Paolo pointed out it is not the TPR associated bug, and we should >> figure out why there is an interrupt window exit after the first EOI. > > Yeah, seems like QEMU bug. QEMU does KVM_INTERRUPT(62) ioctl after KVM > exits with KVM_EXIT_IRQ_WINDOW_OPEN, which QEMU requested while the > guest was printing. The printing calls > > serial_update_irq() -> qemu_irq_lower() -> qemu_set_irq() -> > gsi_handler() -> qemu_set_irq() -> pic_irq_request() -> > apic_deliver_pic_intr() -> kvm_handle_interrupt() > > kvm_handle_interrupt() does > > interrupt_request |= CPU_INTERRUPT_HARD > > which later calls cpu_get_pic_interrupt() in kvm_arch_pre_run(), but > that function uses stale information from APIC and injects 62 again. > If we synchronized the APIC, then the test would #GP, because there > would be no injectable interrupt in LAPIC or PIC, so pic_read_irq() > would return 15, thinking it was spurious. > > I think the bug starts in pic_irq_request(), which should not touch > LAPIC. The patch below makes it work (just the second hunk is > sufficient), but it's still far from sane code ... Thanks for the analysis, Radim! :) Regards, Wanpeng Li -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
