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SubjectRe: [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 <> 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 <>
>>> Signed-off-by: Tao Xu <>
>>> Signed-off-by: Xiaoyao Li <>
>> 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.

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