linux-kernel - Re: [PATCH v2 4/4] KVM: LAPIC: Don't silently accept bad vectors

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Date:   Fri, 13 Oct 2017 22:31:11 +0200
From:   Radim Krčmář <rkrcmar@...hat.com>
To:     Wanpeng Li <kernellwp@...il.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 v2 4/4] KVM: LAPIC: Don't silently accept bad vectors

2017-10-13 19:36+0200, Radim Krčmář:
> 2017-10-13 09:17+0800, Wanpeng Li:
> > 2017-10-04 22:44 GMT+08:00 Radim Krčmář <rkrcmar@...hat.com>:
> > > 2017-10-04 22:16+0800, Wanpeng Li:
> > >> 2017-10-04 20:01 GMT+08:00 Radim Krčmář <rkrcmar@...hat.com>:
> > >> > 2017-10-04 15:56+0800, Wanpeng Li:
> > >> >> 2017-10-04 1:53 GMT+08:00 Radim Krčmář <rkrcmar@...hat.com>:
> > >> >> > 2017-09-28 18:04-0700, Wanpeng Li:
> > >> >> >> @@ -946,6 +965,11 @@ static int __apic_accept_irq(struct kvm_lapic *apic, int delivery_mode,
> > >> >> >>       int result = 0;
> > >> >> >>       struct kvm_vcpu *vcpu = apic->vcpu;
> > >> >> >>
> > >> >> >> +     if (unlikely(vector < 16) && delivery_mode == APIC_DM_FIXED) {
> > >> >> >> +             apic_error(apic, APIC_ESR_RECVILL);
> > >> >> >
> > >> >> > The error is also triggered if lowest priority is supported and tries to
> > >> >> > deliver an invalid vector.
> > >> >>
> > >> >> Could you point out this in SDM? :)
> > >> >
> > >> > In section 10.5.3 Error Handling:
> > >> >
> > >> >   If the local APIC does not support the sending of lowest-priority IPIs
> > >> >   and software writes the ICR to send a lowest-priority IPI with an
> > >> >   illegal vector, the local APIC sets only the “redirectible IPI” error
> > >> >   bit.
> > >> >
> > >> > Hence, if local APIC does support lowest-priority, then it throws the
> > >> > same error as fixed.  (KVM does support lowest-priority.)
> > >>
> > >> Yeah, I read the section before but I misunderstand it. It seems that
> > >> the section means it just occurs when the local APIC does not support
> > >> the sending of lowest-priority IPIs?
> > >
> > > I think so.
> > 
> > I see Virtualbox just captures Fixed delivery mode for error handling.
> 
> Hm, it doesn't even inject an error on destination of the
> lowest-priority interrupt and just drop it?
> 
> I can't interpret the SDM in any other way, though:
> 
>   When an interrupt vector in the range of 0 to 15 is sent or received
>   through the local APIC, the APIC indicates an illegal vector in its
>   Error Status Register (see Section 10.5.3, “Error Handling”).
> 
> and we support lowest-priority interrupts, because if we didn't, then
> 
>  The interrupt is not processed and hence the “Send Illegal Vector” bit
>  is not set in the ESR.
> 
> I'll go for a quick bare-metal test ...

Turns out my machine doesn't support for lowest priority IPIs (probably
got killed with FSB), so all I get is error 0x10.