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From:   Jim Mattson <jmattson@google.com>
Date:   Mon, 2 Nov 2020 14:53:48 -0800
Message-ID: <CALMp9eTrsz4fq19HXGjfQF3GmsQ7oqGW9GXVnMYXtwnPmJcsOA@mail.gmail.com>
Subject: Re: [PATCH] KVM: VMX: Enable Notify VM exit
To:     Tao Xu <tao3.xu@intel.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <sean.j.christopherson@intel.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H . Peter Anvin" <hpa@zytor.com>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        kvm list <kvm@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Xiaoyao Li <xiaoyao.li@intel.com>
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On Sun, Nov 1, 2020 at 10:14 PM Tao Xu <tao3.xu@intel.com> wrote:
>
> There are some cases that malicious virtual machines can cause CPU stuck
> (event windows don't open up), e.g., infinite loop in microcode when
> nested #AC (CVE-2015-5307). No event window obviously means no events,
> e.g. NMIs, SMIs, and IRQs will all be blocked, may cause the related
> hardware CPU can't be used by host or other VM.
>
> To resolve those cases, it can enable a notify VM exit if no
> event window occur in VMX non-root mode for a specified amount of
> time (notify window).
>
> Expose a module param for setting notify window, default setting it to
> the time as 1/10 of periodic tick, and user can set it to 0 to disable
> this feature.
>
> TODO:
> 1. The appropriate value of notify window.
> 2. Another patch to disable interception of #DB and #AC when notify
> VM-Exiting is enabled.
>
> Co-developed-by: Xiaoyao Li <xiaoyao.li@intel.com>
> Signed-off-by: Tao Xu <tao3.xu@intel.com>
> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>

Do you have test cases?