linux-kernel - Re: [PATCH] KVM: nVMX: Fix try to emulate "Acknowledge interrupt on exit" for interrupt which belongs to L1

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Date:   Mon, 31 Jul 2017 20:17:47 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH] KVM: nVMX: Fix try to emulate "Acknowledge interrupt on
 exit" for interrupt which belongs to L1

2017-07-31 20:10 GMT+08:00 Paolo Bonzini <pbonzini@...hat.com>:
> On 30/07/2017 09:31, Wanpeng Li wrote:
>> From: Wanpeng Li <wanpeng.li@...mail.com>
>>
>> ------------[ cut here ]------------
>>  WARNING: CPU: 5 PID: 2288 at arch/x86/kvm/vmx.c:11124 nested_vmx_vmexit+0xd64/0xd70 [kvm_intel]
>>  CPU: 5 PID: 2288 Comm: qemu-system-x86 Not tainted 4.13.0-rc2+ #7
>>  RIP: 0010:nested_vmx_vmexit+0xd64/0xd70 [kvm_intel]
>> Call Trace:
>>   vmx_check_nested_events+0x131/0x1f0 [kvm_intel]
>>   ? vmx_check_nested_events+0x131/0x1f0 [kvm_intel]
>>   kvm_arch_vcpu_ioctl_run+0x5dd/0x1be0 [kvm]
>>   ? vmx_vcpu_load+0x1be/0x220 [kvm_intel]
>>   ? kvm_arch_vcpu_load+0x62/0x230 [kvm]
>>   kvm_vcpu_ioctl+0x340/0x700 [kvm]
>>   ? kvm_vcpu_ioctl+0x340/0x700 [kvm]
>>   ? __fget+0xfc/0x210
>>   do_vfs_ioctl+0xa4/0x6a0
>>   ? __fget+0x11d/0x210
>>   SyS_ioctl+0x79/0x90
>>   do_syscall_64+0x8f/0x750
>>   ? trace_hardirqs_on_thunk+0x1a/0x1c
>>   entry_SYSCALL64_slow_path+0x25/0x25
>>
>> This can be reproduced by booting L1 guest w/ 'noapic' grub parameter, which
>> means that tells the kernel to not make use of any IOAPICs that may be present
>> in the system.
>>
>> There is a scenario when !kvm_cpu_has_interrupt(vcpu) && external_intr in
>> vmx_check_nested_events() which means that there is a pending interrupt from
>> L0's qemu device model which should be injected to L1, we should not try to
>> emualte "Acknowledge interrupt on exit" for this interrupt.
>>
>> This patch fixes it by trying to emulate "Acknowledge interrupt on exit" if L1
>> asks us to.
>
> The commit message is not clear; can you rephrase?

Actually external_intr here is the req_int_win passed from
vcpu_enter_guest() which means that the L0's qemu request an irq
window. I observed the secanrio !kvm_cpu_has_interrupt(vcpu) && L0's
qemu request an irq window is true. Which means that there is a
pending interrupt from L0's qemu device model which should be injected
to L1, we should not try to emualte "Acknowledge interrupt on exit"
for this interrupt.

Regards,
Wanpeng Li

>
>> 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 | 5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 2737343..92eb0f75 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -11118,8 +11118,9 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
>>
>>       vmx_switch_vmcs(vcpu, &vmx->vmcs01);
>>
>> -     if ((exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
>> -         && nested_exit_intr_ack_set(vcpu)) {
>> +     if (exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT &&
>> +             kvm_cpu_has_interrupt(vcpu) &&
>> +             nested_exit_intr_ack_set(vcpu)) {
>
> Maybe check nested_exit_intr_ack_set first.
>
> Paolo
>
>>               int irq = kvm_cpu_get_interrupt(vcpu);
>>               WARN_ON(irq < 0);
>>               vmcs12->vm_exit_intr_info = irq |
>>
>