linux-kernel - Re: [PATCH 02/13] KVM: nVMX: Open a window for pending nested VMX preemption timer

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Message-ID: <CALMp9eTnOs=MMVThBf032XVydj1F40P0Kui7VFAn9F=idLAFPw@mail.gmail.com>
Date:   Tue, 28 Apr 2020 14:39:32 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.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 02/13] KVM: nVMX: Open a window for pending nested VMX
 preemption timer

On Wed, Apr 22, 2020 at 7:26 PM Sean Christopherson
<sean.j.christopherson@...el.com> wrote:
>
> Add a kvm_x86_ops hook to detect a nested pending "hypervisor timer" and
> use it to effectively open a window for servicing the expired timer.
> Like pending SMIs on VMX, opening a window simply means requesting an
> immediate exit.
>
> This fixes a bug where an expired VMX preemption timer (for L2) will be
> delayed and/or lost if a pending exception is injected into L2.  The
> pending exception is rightly prioritized by vmx_check_nested_events()
> and injected into L2, with the preemption timer left pending.  Because
> no window opened, L2 is free to run uninterrupted.
>
> Fixes: f4124500c2c13 ("KVM: nVMX: Fully emulate preemption timer")
> Reported-by: Jim Mattson <jmattson@...gle.com>
> Cc: Oliver Upton <oupton@...gle.com>
> Cc: Peter Shier <pshier@...gle.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
Reviewed-by: Jim Mattson <jmattson@...gle.com>