Re: locking user space memory in kernel

[Manfred Spraul]

Roland Dreier wrote:

>    Manfred> I think just get_user_pages() should be sufficient: the
>    Manfred> pages won't be swapped out. You don't need to set
>    Manfred> VM_LOCKED in vma->vm_flags to prevent the swap out. In
>    Manfred> the worst case, the pte is cleared a that will cause a
>    Manfred> soft page fault, but the physical address won't
>    Manfred> change. Multiple get_user_pages() calls on overlapping
>    Manfred> regions are ok, the page count is an atomic_t, at least
>    Manfred> 24-bit large.
>
> There is one case that we ran into where the physical address can
> change: if a process does a fork() and then triggers COW.
You are right.
What should happen if there are registered transfers during fork()? Copy 
the pages during the fork() syscall?

--
   Manfred

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