Re: some other memory considerations.

[Marcus Brinkmann]

At Tue, 26 Oct 2004 14:08:03 +0200,
Bas Wijnen <address@hidden> wrote:
> L4 allows it, indeed.  However, our current ideas of the Hurd don't.  In 
> fact, they don't allow it even if you are a pager.

Let's say that our design should not rely on this being possible.
 
> Mapping memory to an other task costs kernel memory.  Therefore, it can 
> be used for a denial of service attack against the system.  Because of 
> that, it must be a restricted operation, which can only be performed by 
> trusted tasks (and will in practice only be performed by physmem, I 
> think.)  Note also that pagers are not trusted tasks.  So for a pager to 
> map memory to a task, it has to ask physmem to do it.  Granting memory 
> is not a problem, and will be allowed.  I'm not sure if it would be used 
> much, though.

Granting memory across address spaces is probably OK, but I am not
sure.  In any case, the only thing we need (and can allow) is granting
memory within your own address space (ie, change the vaddr of a mapping).

Marcus