linux-kernel - RE: [RESEND PATCH 5/6] KVM: x86/VMX: add kvm_vmx_reinject_nmi

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Date:   Fri, 11 Nov 2022 18:06:12 +0000
From:   "Li, Xin3" <xin3.li@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "Tian, Kevin" <kevin.tian@...el.com>
Subject: RE: [RESEND PATCH 5/6] KVM: x86/VMX: add kvm_vmx_reinject_nmi_irq()
 for NMI/IRQ reinjection

> On Fri, Nov 11, 2022 at 01:48:26PM +0100, Paolo Bonzini wrote:
> > On 11/11/22 13:19, Peter Zijlstra wrote:
> > > On Fri, Nov 11, 2022 at 01:04:27PM +0100, Paolo Bonzini wrote:
> > > > On Intel you can optionally make it hold onto IRQs, but NMIs are
> > > > always eaten by the VMEXIT and have to be reinjected manually.
> > >
> > > That 'optionally' thing worries me -- as in, KVM is currently
> > > opting-out?
> >
> > Yes, because "If the “process posted interrupts” VM-execution control
> > is 1, the “acknowledge interrupt on exit” VM-exit control is 1" (SDM
> > 26.2.1.1, checks on VM-Execution Control Fields).  Ipse dixit.  Posted
> > interrupts are available and used on all processors since I think Ivy Bridge.
> 
> (imagine the non-coc compliant reaction here)
> 
> So instead of fixing it, they made it worse :-(
> 
> And now FRED is arguably making it worse again, and people wonder why I
> hate virt...

Maybe I take it wrong, but FRED doesn't make anything worse. Fred entry
code will call external_interrupt() immediately for IRQs.

You really really don't like the context how VMX dispatches NMI/IRQs (which has
been there for a long time), right?

As you said, what if we do not call DEFINE_IDTENTRY_*(func) but the internal
IRQ handlers __func?  That way we take out the setup for RCU/lockdep/etc.