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?
> +
> + on_each_cpu_mask(mm_cpumask(mm), enable_lam_func, mm, true);
> +out:
> + mutex_unlock(&mm->context.lock);
> + return ret;
> +}
