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 14:10:17 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     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

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?

> 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 |
>