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Subject: Re: [PATCH] KVM: VMX: Enable Notify VM exit
To:     Jim Mattson <jmattson@google.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>
References: <20201102061445.191638-1-tao3.xu@intel.com>
 <CALMp9eTrsz4fq19HXGjfQF3GmsQ7oqGW9GXVnMYXtwnPmJcsOA@mail.gmail.com>
From:   Tao Xu <tao3.xu@intel.com>
Message-ID: <d4388899-665f-8012-c609-8162fa7015ae@intel.com>
Date:   Tue, 3 Nov 2020 14:12:42 +0800
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On 11/3/20 6:53 AM, Jim Mattson wrote:
> 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?
> 
Not yet, because we are waiting real silicon to do some test. I should 
add RFC next time before I test it in hardware.