linux-kernel - Re: [PATCH] KVM: VMX: Enable Notify VM exit

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Date:   Tue, 3 Nov 2020 14:24:22 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Tao Xu <tao3.xu@...el.com>, Jim Mattson <jmattson@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM: VMX: Enable Notify VM exit

On 11/3/2020 2:12 PM, Tao Xu wrote:
> 
> 
> On 11/3/20 6:53 AM, Jim Mattson wrote:
>> On Sun, Nov 1, 2020 at 10:14 PM Tao Xu <tao3.xu@...el.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@...el.com>
>>> Signed-off-by: Tao Xu <tao3.xu@...el.com>
>>> Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
>>
>> Do you have test cases?
>>

yes we have. The nested #AC (CVE-2015-5307) is a known test case, though 
we need to tweak KVM to disable interception #AC for it.

> Not yet, because we are waiting real silicon to do some test. I should 
> add RFC next time before I test it in hardware.