linux-kernel - Re: [PATCH v2 2/2] KVM: X86: Fix loss of exception which has not yet injected

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Date:   Thu, 24 Aug 2017 12:30:55 +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 v2 2/2] KVM: X86: Fix loss of exception which has not yet injected

2017-08-23 20:27 GMT+08:00 Paolo Bonzini <pbonzini@...hat.com>:
> On 23/08/2017 12:23, Wanpeng Li wrote:
>> @@ -6341,7 +6345,8 @@ static int inject_pending_event(struct kvm_vcpu *vcpu, bool req_int_win)
>>       int r;
>>
>>       /* try to reinject previous events if any */
>> -     if (vcpu->arch.exception.pending) {
>> +     if (vcpu->arch.exception.pending ||
>> +             vcpu->arch.exception.injected) {
>>               trace_kvm_inj_exception(vcpu->arch.exception.nr,
>>                                       vcpu->arch.exception.has_error_code,
>>                                       vcpu->arch.exception.error_code);
>> @@ -6357,6 +6362,11 @@ static int inject_pending_event(struct kvm_vcpu *vcpu, bool req_int_win)
>>               }
>>
>>               r = kvm_x86_ops->queue_exception(vcpu);
>> +             if (r == 0 && vcpu->arch.exception.pending &&
>> +                     !vcpu->arch.exception.injected) {
>> +                     vcpu->arch.exception.pending = false;
>> +                     vcpu->arch.exception.injected = true;
>> +             }
>>               return r;
>>       }
>>
>
> There are some changes needed here:
>
> - this "if" should check only .injected and call
> kvm_x86_ops->queue_exception.  The "if" for .pending, which handles
> rflags/dr7, assigns false to .pending and true to .injected, and also
> calls kvm_x86_ops->queue_exception, should be after the call to
> check_nested_events.
>
> - in the call to inject_pending_event, the "else" should have a
>
>         WARN_ON(vcpu->arch.exception.pending);
>
> just for completeness.
>
>
> Also, nested_vmx_check_exception has to be moved from
> vmx_queue_exception to vmx_check_nested_events, so that
> nested_run_pending is checked correctly.  Something like this:
>
>         if (vcpu->arch.exception.pending &&
>             nested_vmx_check_exception(vcpu, &exit_qual)) {
>                 if (vmx->nested.nested_run_pending)
>                         return -EBUSY;
>
>                 nested_vmx_inject_exception_vmexit(vcpu, exit_qual);
>                 return 0;
>         }
>
> Maybe you can have:
>
> - patch 1 which I'll apply now
>
> - patch 2 is the same as this one, with only the above changes to
> inject_pending_event and the WARN_ON.
>
> - patch 3 moves the nested_vmx_inject_exception_vmexit call from
> nested_vmx_check_exception to vmx_queue_exception.
>
> - patch 4 moves the code to vmx_check_nested_events and add the
> nested_run_pending check, fixing the original bug.
>
> As to GET/SET_VCPU_EVENTS, for now I would not do any change.  Instead,
> we can do
>
>         /*
>          * FIXME: pass injected and pending separately.  This is only
>          * needed for nested virtualization, whose state cannot be
>          * migrated yet.  For now we combine them just in case.
>          */
>         events->exception.injected =
>                 (vcpu->arch.exception.pending ||
>                  vcpu->arch.exception.injected) &&
>                 !kvm_exception_is_soft(vcpu->arch.exception.nr);
>         }
>

I complete all the comments in v3, thanks for the review. :)

Regards,
Wanpeng Li

> and set_vcpu_events can just set .injected = false.  Separating the two
> will need a separate capability and KVM_ENABLE_CAP.
>
> Paolo
>
>>
>> diff --git a/tools/arch/x86/include/uapi/asm/kvm.h b/tools/arch/x86/include/uapi/asm/kvm.h
>> index c2824d0..7c55916 100644
>> --- a/tools/arch/x86/include/uapi/asm/kvm.h
>> +++ b/tools/arch/x86/include/uapi/asm/kvm.h
>> @@ -296,9 +296,9 @@ struct kvm_reinject_control {
>>  struct kvm_vcpu_events {
>>       struct {
>>               __u8 injected;
>> +             __u8 pending;
>>               __u8 nr;
>>               __u8 has_error_code;
>> -             __u8 pad;
>>               __u32 error_code;
>>       } exception;
>>       struct {
>
> I think you don't need t

Agreed.