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

Kirill A. Shutemov
2022-06-10T18:06:44Z

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.

--
Kirill A. Shutemov