Re: help with understanding GPA/GVA issues

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Gregory Haskins wrote:
>>>   
>>>       
>> Yes, you can pass through any gva.  There are couple of things to be 
>> aware of though.  When passing a gva, you have to be sure that the gva 
>> is actually mapped in memory as KVM cannot cause Linux to fault in a 
>> page.
>>     
>
> Cool!  Ya, I totally understand and agree that it has to be "DMA" class
> memory that is mapped and pinned in guest context.  IIUC you basically
> need to follow the same rules as you would for a DMA based device in a
> bare-metal scenario.
>
>   

Note that passing a virtual address is highly discouraged as its meaning 
can change from vcpu to vcpu, it might not be mapped, translation is 
slow, etc.  Just let the guest do the translation.

> On this topic:  I know there has been talk going on of giving each VM
> its own linux va context.  IIUC, when that happens we wouldn't need the
> gva_to_hpa type functions, right?  We could use things like
> copy_to_user(), etc?  Out of curiosity, what's the status of that
> project?
>   

We have something running at qumranet, will be sent out soon.  I am 
somewhat discouraged in trying to get the thing to page -- Shaohua's 
approach is much simpler.



-------------------------------------------------------------------------
This SF.net email is sponsored by: Splunk Inc.
Still grepping through log files to find problems?  Stop.
Now Search log events and configuration files using AJAX and a browser.
Download your FREE copy of Splunk now >>  http://get.splunk.com/