Re: uvm_unmap() vs. uvm_deallocate()

[tzsz <writing.segfaults%gmail.com@localhost>]

Hello Stephan,

uvm_deallocate is a wrapper for uvm_unmap. It calls unmap after checking 
3 things:

- size is not 0
- address starts at a page. If not, it is rounded
- address + size is at the end of a page, otherwise, size is also rounded

A thing to look out for here is that unmap takes a pointer to the end 
while deallocate uses the size instead and it is not possible to set the 
flags using deallocate.

From what I understand in regard to sys_shmdt (sysv_shm.c), the address 
in this case cannot be influenced by the user/userland. This would make 
the checks introduced by deallocate not necessary.

Kind regards


Am 13.01.25 um 14:06 schrieb Stephan:
> Hello,
>
> what is the difference between uvm_unmap() and uvm_deallocate()?
>
> It does not become clear to me from what is written in uvm_map(9):
>
>
> uvm_unmap() removes a valid mapping, from start to end, in map map, which
>       must be unlocked.
>
> uvm_deallocate() deallocates kernel memory in map map from address start
>       to start + size.
>
>
> uvm_deallocate() is used e.g. in sysv_shm.c, in which case I would
> have expected uvm_unmap().
>
>
> Thanks,
>
> Stephan