linux-kernel - Re: [PATCH] KVM: nVMX: Fix trying to cancel vmlauch/vmresume

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Message-ID: <CANRm+Cx=js6_bXNJ3U1toh33msL5den2mXfUWLfsk89FssasJw@mail.gmail.com>
Date:   Sat, 19 Aug 2017 04:34:51 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Radim Krčmář <rkrcmar@...hat.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>, Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH] KVM: nVMX: Fix trying to cancel vmlauch/vmresume

2017-08-18 21:00 GMT+08:00 Radim Krčmář <rkrcmar@...hat.com>:
> 2017-08-17 18:30-0700, Wanpeng Li:
>> From: Wanpeng Li <wanpeng.li@...mail.com>
>>
>> ------------[ 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 running L2 next
>> instead of L1 in the queue exception path.
>>
>> Cc: Paolo Bonzini <pbonzini@...hat.com>
>> Cc: Radim Krčmář <rkrcmar@...hat.com>
>> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
>> ---
>>  arch/x86/kvm/vmx.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index e398946..3e64a9b 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -2466,6 +2466,9 @@ static int nested_vmx_check_exception(struct kvm_vcpu *vcpu)
>>       struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
>>       unsigned int nr = vcpu->arch.exception.nr;
>>
>> +     if (to_vmx(vcpu)->nested.nested_run_pending)
>> +             return 0;
>
> This will inject the exception into L2, even though L1 should get it.
> We can't return 1 either, as that would just drop the exception ...
>
> Seems like we should request an immediate VM exit from L2 and keep the
> exception for L1 pending for a subsequent nested VM exit.

Good point, please review v2. :)

Regards,
Wanpeng Li