2017-08-22 7:09 GMT+08:00 Wanpeng Li <kernellwp@xxxxxxxxx>: > 2017-08-22 6:55 GMT+08:00 Wanpeng Li <kernellwp@xxxxxxxxx>: >> 2017-08-22 0:20 GMT+08:00 Radim Krčmář <rkrcmar@xxxxxxxxxx>: >>> 2017-08-18 07:11-0700, Wanpeng Li: >>>> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> >>>> >>>> ------------[ cut here ]------------ >>>> WARNING: CPU: 7 PID: 3861 at /home/kernel/ssd/kvm/arch/x86/kvm//vmx.c:11299 nested_vmx_vmexit+0x176e/0x1980 [kvm_intel] >>>> CPU: 7 PID: 3861 Comm: qemu-system-x86 Tainted: G W OE 4.13.0-rc4+ #11 >>>> RIP: 0010:nested_vmx_vmexit+0x176e/0x1980 [kvm_intel] >>>> Call Trace: >>>> ? kvm_multiple_exception+0x149/0x170 [kvm] >>>> ? handle_emulation_failure+0x79/0x230 [kvm] >>>> ? load_vmcs12_host_state+0xa80/0xa80 [kvm_intel] >>>> ? check_chain_key+0x137/0x1e0 >>>> ? reexecute_instruction.part.168+0x130/0x130 [kvm] >>>> nested_vmx_inject_exception_vmexit+0xb7/0x100 [kvm_intel] >>>> ? nested_vmx_inject_exception_vmexit+0xb7/0x100 [kvm_intel] >>>> vmx_queue_exception+0x197/0x300 [kvm_intel] >>>> kvm_arch_vcpu_ioctl_run+0x1b0c/0x2c90 [kvm] >>>> ? kvm_arch_vcpu_runnable+0x220/0x220 [kvm] >>>> ? preempt_count_sub+0x18/0xc0 >>>> ? restart_apic_timer+0x17d/0x300 [kvm] >>>> ? kvm_lapic_restart_hv_timer+0x37/0x50 [kvm] >>>> ? kvm_arch_vcpu_load+0x1d8/0x350 [kvm] >>>> kvm_vcpu_ioctl+0x4e4/0x910 [kvm] >>>> ? kvm_vcpu_ioctl+0x4e4/0x910 [kvm] >>>> ? kvm_dev_ioctl+0xbe0/0xbe0 [kvm] >>>> >>>> The flag "nested_run_pending", which can override the decision of which should run >>>> next, L1 or L2. nested_run_pending=1 means that we *must* run L2 next, not L1. This >>>> is necessary in particular when L1 did a VMLAUNCH of L2 and therefore expects L2 to >>>> be run (and perhaps be injected with an event it specified, etc.). Nested_run_pending >>>> is especially intended to avoid switching to L1 in the injection decision-point. >>>> >>>> I catch this in the queue exception path, this patch fixes it by requesting >>>> an immediate VM exit from L2 and keeping the exception for L1 pending for a >>>> subsequent nested VM exit. >>>> >>>> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> >>>> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx> >>>> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> >>>> --- >>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c >>>> @@ -6356,8 +6356,8 @@ static int inject_pending_event(struct kvm_vcpu *vcpu, bool req_int_win) >>>> kvm_update_dr7(vcpu); >>>> } >>> >>> Hm, we shouldn't execute the code above if exception won't be injected. >>> >>>> >>>> - kvm_x86_ops->queue_exception(vcpu); >>>> - return 0; >>> >>> vmx_complete_interrupts() assumes that the exception is always injected, >>> so it would be dropped by kvm_clear_exception_queue(). >>> >>> I'm starting to wonder whether getting rid of nested_run_pending >>> wouldn't be nicer. >> >> Yeah, I rethink of your concern for nested_run_pending w/ return value >> is 0, actually the path in the calltrace is the else branch in >> nested_vmx_check_exception(), an exception will be injected to L2 by >> L1 if L1 owns this exception, otherwise injected by L0 directly. For >> the nested_run_pending w/ return value is 0 stuff, we can treat it as >> L0 injects the exception to L2 directly. So there is no exception is >> injected to wrong guest. > > I just sent out v3 to move the nested_run_pending stuff to the else branch. I can still encounter the splat w/ v3 due to #PF, so v1 is still better. Regards, Wanpeng Li
