Re: [Xen-devel] [PATCH 1/3] Nested VMX: update nested paging mode when vmswitch is in progress

["Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>]

Egger, Christoph wrote on 2014-01-20:
> On 14.01.14 08:38, Zhang, Yang Z wrote:
>> Jan Beulich wrote on 2014-01-14:
>>>>>> On 14.01.14 at 03:33, "Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>
> wrote:
>>>> Zhang, Yang Z wrote on 2013-12-24:
>>>> 
>>>> Any comments ?
>>> 
>>> Considering Christoph's comments and reservations, if you can't
>>> alone deal with this I think you should work with the AMD people to
>>> eliminate or address his concerns.
>>> 
>> 
>> Yes. But the problem puzzled me is that Christoph said nested SVM works
>> well w/o my patch which I cannot understand. Because according my
>> analysis in previous thread, it also buggy in AMD side. But if they
>> really solved the issue in their side, I wonder how they fix it.
>> Perhaps I can use the same solution in VMX side without touch the
>> common code.
>> 
>> Christoph, can you help to check it? thanks.
> 
> The fix I mentioned solves the vmswitch problem on AMD side.

But the current code is buggy with your fixing even in AMD side, see below 
scenario:
virtual vmentry: 
    Expected result: nested mode is being updated.
    Current result in SVM: 
          !vcpu_in_guestmode and vmswitch_in_progress:  L1's paging mode is 
updated.  Wrong.

I cannot understand why you said it is working.

> The page mode problem you discovered is a seperate issue for both SVM
> and VMX that needs to be addressed.
> 
> Christoph


Best regards,
Yang



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