On Mon, Aug 15, 2022 at 03:37:16PM +0200, Peter Zijlstra wrote:
> On Mon, Aug 15, 2022 at 07:17:58AM +0300, Kirill A. Shutemov wrote:
>
> > +static void enable_lam_func(void *mm)
> > +{
> > + struct mm_struct *loaded_mm = this_cpu_read(cpu_tlbstate.loaded_mm);
> > + unsigned long lam_mask;
> > + unsigned long cr3;
> > +
> > + if (loaded_mm != mm)
> > + return;
> > +
> > + lam_mask = READ_ONCE(loaded_mm->context.lam_cr3_mask);
> > +
> > + /* Update CR3 to get LAM active on the CPU */
> > + cr3 = __read_cr3();
> > + cr3 &= ~(X86_CR3_LAM_U48 | X86_CR3_LAM_U57);
> > + cr3 |= lam_mask;
> > + write_cr3(cr3);
> > + set_tlbstate_cr3_lam_mask(lam_mask);
> > +}
> > +
> > +static int prctl_enable_tagged_addr(struct mm_struct *mm, unsigned long nr_bits)
> > +{
> > + int ret = 0;
> > +
> > + if (!cpu_feature_enabled(X86_FEATURE_LAM))
> > + return -ENODEV;
> > +
> > + mutex_lock(&mm->context.lock);
> > +
> > + /* Already enabled? */
> > + if (mm->context.lam_cr3_mask) {
> > + ret = -EBUSY;
> > + goto out;
> > + }
> > +
> > + if (!nr_bits) {
> > + ret = -EINVAL;
> > + goto out;
> > + } else if (nr_bits <= 6) {
> > + mm->context.lam_cr3_mask = X86_CR3_LAM_U57;
> > + mm->context.untag_mask = ~GENMASK(62, 57);
> > + } else {
> > + ret = -EINVAL;
> > + goto out;
> > + }
> > +
> > + /* Make lam_cr3_mask and untag_mask visible on other CPUs */
> > + smp_mb();
>
> smp_mb() doesn't make visible -- it is about ordering, what does it
> order against that the below on_each_cpu_mask() doesn't already take
> care of?
You are right it is redundant. I will drop it.
--
Kiryl Shutsemau / Kirill A. Shutemov
