Re: perl hypervisor interface

[Avery Pennarun <apenwarr@nit.ca>]

On Fri, Jul 09, 2004 at 05:02:27PM +0100, Keir Fraser wrote:

> > One bit I left out from the libxc do_dom0_op() procedure, was calling mlock()
> > on the dom0_op struct before passing it into the ioctl().
> > When does the mlock() come into play?
> 
> Xen doesn't do paging, so any memory buffers you pass to the dom0_op
> hypercall (including the dom0_op_t structure itself) must be resident
> when Xen is entered. If the buffer is allocated in-kernel then this
> isn't a problem, as Linux doesn't page itself. In user space we must
> use mlock() to force the buffer to be resident.

Wouldn't it be better to have the ioctl() auto-mlock() the memory area,
rather than trusting userspace apps to know what they're doing?  In general,
calls from userspace shouldn't be able to *accidentally* crash the kernel...
at least not without asking the kernel for permission first :) 

Have fun,

Avery


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