linux-kernel - Re: [PATCH] KVM: LAPIC: Level-sensitive interrupts are not support for LINT1

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Date:   Sun, 15 Oct 2017 10:14:40 +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: LAPIC: Level-sensitive interrupts are not support
 for LINT1

2017-10-14 4:43 GMT+08:00 Radim Krčmář <rkrcmar@...hat.com>:
> 2017-10-12 21:27-0700, Wanpeng Li:
>> From: Wanpeng Li <wanpeng.li@...mail.com>
>>
>> SDM 10.5.1 mentioned:
>>  Software should always set the trigger mode in the LVT LINT1 register to 0 (edge
>>  sensitive). Level-sensitive interrupts are not supported from LINT1.
>>
>> I can intercept both Linux/windows 7/windows 2016 guests on my hand will set
>> Level-sensitive trigger mode to LVT LINT1 register during boot.
>
> And there is no problem with that, software can do that, delivery
> through LINT1 is just undefined with that (most likely behaviors are:
> deliver as edge and don't deliver.).
>
>> This patch avoids the software too fool to set the level-sensitive trigger mode
>> to LVT LINT1 register.
>
> The software should see the value it writes, though, so the current
> behavior is better.
>
> Do we hit a KVM bug if the software uses APIC_LVT_LEVEL_TRIGGER?

I check the Virtualbox has the same logic.

Regards,
Wanpeng Li

>
> Thanks.
>
>> Cc: Paolo Bonzini <pbonzini@...hat.com>
>> Cc: Radim Krčmář <rkrcmar@...hat.com>
>> Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
>> ---
>>  arch/x86/kvm/lapic.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
>> index a778f1a..26593c7 100644
>> --- a/arch/x86/kvm/lapic.c
>> +++ b/arch/x86/kvm/lapic.c
>> @@ -1758,6 +1758,8 @@ int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
>>                       val |= APIC_LVT_MASKED;
>>
>>               val &= apic_lvt_mask[(reg - APIC_LVTT) >> 4];
>> +             if (reg == APIC_LVT1)
>> +                     val &= ~APIC_LVT_LEVEL_TRIGGER;
>>               kvm_lapic_set_reg(apic, reg, val);
>>
>>               break;
>> --
>> 2.7.4
>>