Re: kvm guest memory management

[Anthony Liguori <aliguori-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

Avi Kivity wrote:
> Dong, Eddie wrote:
>   
>> There are couple reasons that g2h can't server this.
>> A VT-d device or EPT/NPT table need to translate from guest physical 
>> to machine physical address, while g2h uses host mode va as index.
>> Other reason is that g2h also include host user space memory & kernel
>> memory which guest should never touch. (A bad programmed VT-d device
>> may modify the memory listed by VT-d table).
>>
>>   
>>     
>
> For EPT, we can't use the host page tables because EPT does not support 
> the dirty bit.  So EPT requires duplication of the page tables anyway.
>   

EPT fill in the dirty bit?  To track dirty memory, you would have to
read protect portions of the EPT?  That seems quite unfortunate...

Regards,

Anthony Liguori

>> Dirty tracking can certainly be serviced even using p2m solely.
>>
>>   
>>     
>>> User-allocated memory will enable the following features:
>>> - s390 support
>>> - guest swapping
>>> - page migration (where a guest is migrated from one NUMA node
>>> to another)
>>> - in conjunction with a de-duplicating file system, page sharing
>>> among guests 
>>> - inter-guest shared memory (mmap() one file in two or more guests)
>>> - easier use of huge pages
>>> - more?
>>>
>>>     
>>>       
>> This doesn't conflict with my suggestion though the p2m table then
>> need to be dynamically modifed in case swapping happens.
>>   
>>     
>
> The nice thing about using the host page tables is that it's 
> automatically updated to reflect changes in mapping.  Translating a page 
> (gfn_to_page) becomes a call to get_user_pages().
>
>
>   



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