Re: mm->mmap_sem

[James Simmons <jsimmons@edgeglobal.com>]

On Sat, 25 Sep 1999, Andrea Arcangeli wrote:

> On Fri, 24 Sep 1999, James Simmons wrote:
> 
> >Just out of curoisty how would one revoke all read-write to that page?
> 
> man mprotect (have a look to PROT_NONE)
> 
> >I know this would be expensive to do.
> 
> If you don't know how to do that how do you know it's expensive? ;)

Well I kind of figured I would have to do what mprotects does. I just
needed someone to say yes mprotect is the way to not allow processes
physical access to a memory region. I just wanted to make sure I was
right. Also I don't want the process to be sent a SIGSEGV. I just want to
put it to sleep for a period of time if it access such a region.

> But indeed you are right: it's a bit expensive as if the pages are just
> allocated you'll have to change all their ptes.

Like mprotect does. How does this compare to unmmaping a large memory
region and putting a process to sleep in a no_page_fault routine.

Is their any way to do cooperative locking kernel side between two memory
regions? If one is being access you can't physically access the other. I
just want to process to sleep not kill it if it attempts this.

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