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

[Koripella Srinivas <talkwithsrinivas@xxxxxxxxxxx>]

I was looking at the user space grant tables but i did not find any code calling the function
"remap_pfn_range" to map the kmalloc ed allocated memory into user space.
What could be the reason?? Or am i missing something

Thanks Mark.

----- Original Message ----
From: Mark Williamson <mark.williamson@xxxxxxxxxxxx>
To: Koripella Srinivas <talkwithsrinivas@xxxxxxxxxxx>
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
Sent: Friday, 6 July, 2007 9:55:48 AM
Subject: Re: [Xen-devel] Grant Tables & mm.c

> " 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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