Re: [PATCHv3 6/8] x86/mm: Provide ARCH_GET_UNTAG_MASK and ARCH_ENABLE_TAGGED_ADDR

["Edgecombe, Rick P" <rick.p.edgecombe@intel.com>]

On Fri, 2022-06-10 at 21:06 +0300, Kirill A. Shutemov wrote:
> On Fri, Jun 10, 2022 at 04:16:01PM +0000, Edgecombe, Rick P wrote:
> > On Fri, 2022-06-10 at 17:35 +0300, Kirill A. Shutemov wrote:
> > > +static int prctl_enable_tagged_addr(unsigned long nr_bits)
> > > +{
> > > +       struct mm_struct *mm = current->mm;
> > > +
> > > +       /* Already enabled? */
> > > +       if (mm->context.lam_cr3_mask)
> > > +               return -EBUSY;
> > > +
> > > +       /* LAM has to be enabled before spawning threads */
> > > +       if (get_nr_threads(current) > 1)
> > > +               return -EBUSY;
> > 
> > Does this work for vfork()? I guess the idea is that locking is not
> > needed below because there is only one thread with the MM, but with
> > vfork() another task could operate on the MM, call fork(), etc. I'm
> > not
> > sure...
> 
> I'm not sure I follow. vfork() blocks parent process until child exit
> or
> execve(). I don't see how it is a problem.

Oh yea, you're right.