Re: [Xen-devel] Grant Tables & mm.c

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> " Linux tends to zap userspace page mappings quite cheerfully
> unless you do something to stop it, could this be your problem?"
>
> What does this mean exactly??

Linux "zaps" mappings when it removes them from pagetables.  Really this 
corresponds to zeroing a pte corresponding to that mapping.

Unless you do something to stop the Linux mm system from treating the grant 
table mappins like "normal" RAM, it will eventually want to simply zero them.  
This will break for grant mappings, since it is not a permitted means of 
unmapping granted memory.

> Any way i can prevent it from happening?

It depends on what you're trying to do...

Have you looked at the userspace grantables driver in our Linux tree?  This 
provides a device for mapping granted memory safely into userspace, handling 
cleanup correctly.  Even if that's not directly useful, maybe you can find 
some code in there that'll help you.

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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