Re: [Xen-devel] Intentional EPT Misconfigurations in xen

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 28/11/16 08:44, 唐伟文 wrote:

Hi,

I have a question that why dose xen hypervisor set entry of ept as invalid (misconfigured) deliberately which will cause VM exit resulting from EPT Misconfigurations. http://xenbits.xenproject.org/gitweb/?p=xen.git;a=commit;h=aa9114edd97b292cd89b3616e3f2089471fd2201 I find the answer in this website which is about a patch of xen. They say that it is necessary to set EPT entry as misconfigured in order to force re-evaluation of memory type as necessary. 

But, I still don't konw why we need to reevaluate memory type? That is to say, why can't we determine memory type during the initialization of EPT. And if it is necessary to do this , which entry of EPT should be misconfigured intentionally?  Thanks

EPT Memory types change at runtime, due to guest actions such as changing the MTRRs, changing CR0.CD, etc, or due to toolstack options such as enabling logdirty mode for live migration.

~Andrew

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