Re: linux page table

[Cong Wang]

On 09/03/2012 02:26 AM, Jiri Kosina wrote:
> On Sun, 2 Sep 2012, Xin Tong wrote:
>
> > > > 3. can two different processes have their CR3 being the same value
> > > > even though they have different first level page tables ?
> > >
> > > Yes, if they are created by clone(CLONE_VM). In such case they share the
> > > same mm_struct, and therefore mm_struct->pgd (which is exactly what is
> > > loaded into cr3 in switch_mm()) is the same.
> >
> > Is this the COW mechanism in linux. what if the cloned process need to
> > have set of its own pages later. do the CR3s for the 2 processes
> > become different at that point ?
>
> That is a different story. COW is applied on fork() (i.e. spawning new
> process), not on clone(CLONE_VM) (i.e. spawning new thread).

Yeah, and unshare(2) does not implement the flag that reverses the 
effects of CLONE_VM.

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