linux-kernel - Re: [PATCH 12/13] KVM: x86: Replace late check_nested

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Message-ID: <20200429170733.GG15992@linux.intel.com>
Date:   Wed, 29 Apr 2020 10:07:33 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Jim Mattson <jmattson@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>, kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Oliver Upton <oupton@...gle.com>,
        Peter Shier <pshier@...gle.com>
Subject: Re: [PATCH 12/13] KVM: x86: Replace late check_nested_events() hack
 with more precise fix

On Wed, Apr 29, 2020 at 06:58:45PM +0200, Paolo Bonzini wrote:
> On 29/04/20 18:45, Sean Christopherson wrote:
> > 
> > Can you just drop 9/13, "Prioritize SMI over nested IRQ/NMI" from kvm/queue?
> > It's probably best to deal with this in a new series rather than trying to
> > squeeze it in.
> 
> With AMD we just have IRQ/NMI/SMI, and it's important to handle SMI in

Ah, forgot about that angle.

> check_nested_events because you can turn SMIs into vmexit without stuff
> such as dual-monitor treatment.  On the other hand there is no MTF and
> we're not handling exceptions yet.  So, since SMIs should be pretty rare
> anyway, I'd rather just add a comment detailing the correct order and
> why we're not following it.  The minimal fix would be to move SMI above
> the preemption timer, right?

Yep, that works for now.

I'd still like to do a full fix for SMI and INIT.  Correctness aside, I
think/hope the changes I have in mind will make it easier to connect the
dots betwen KVM's event priority and the SDM's event priority.  But that
can definitely wait for 5.9.