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References: <20200423022550.15113-1-sean.j.christopherson@intel.com> <20200423022550.15113-3-sean.j.christopherson@intel.com>
In-Reply-To: <20200423022550.15113-3-sean.j.christopherson@intel.com>
From:   Jim Mattson <jmattson@google.com>
Date:   Tue, 28 Apr 2020 14:39:32 -0700
Message-ID: <CALMp9eTnOs=MMVThBf032XVydj1F40P0Kui7VFAn9F=idLAFPw@mail.gmail.com>
Subject: Re: [PATCH 02/13] KVM: nVMX: Open a window for pending nested VMX
 preemption timer
To:     Sean Christopherson <sean.j.christopherson@intel.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Joerg Roedel <joro@8bytes.org>, kvm list <kvm@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Oliver Upton <oupton@google.com>,
        Peter Shier <pshier@google.com>
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On Wed, Apr 22, 2020 at 7:26 PM Sean Christopherson
<sean.j.christopherson@intel.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@google.com>
> Cc: Oliver Upton <oupton@google.com>
> Cc: Peter Shier <pshier@google.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: Jim Mattson <jmattson@google.com>