On Fri, Jan 05, 2018 at 06:12:19PM -0800, Tim Chen wrote: > +static void spec_ctrl_flush_all_cpus(u32 msr_nr, u64 val) > +{ > + int cpu; > + > + get_online_cpus(); > + for_each_online_cpu(cpu) > + wrmsrl_on_cpu(cpu, msr_nr, val); > + put_online_cpus(); > +} > + > +static ssize_t ibrs_enabled_write(struct file *file, > + const char __user *user_buf, > + size_t count, loff_t *ppos) > +{ > + char buf[32]; > + ssize_t len; > + unsigned int enable; > + > + len = min(count, sizeof(buf) - 1); > + if (copy_from_user(buf, user_buf, len)) > + return -EFAULT; > + > + buf[len] = '\0'; > + if (kstrtouint(buf, 0, &enable)) > + return -EINVAL; > + > + if (enable > IBRS_MAX) > + return -EINVAL; > + > + if (!boot_cpu_has(X86_FEATURE_SPEC_CTRL)) { > + ibrs_enabled = IBRS_DISABLED; > + return -EINVAL; > + } > + > + mutex_lock(&spec_ctrl_mutex); > + > + if (enable == IBRS_DISABLED) { > + /* disable IBRS usage */ > + ibrs_admin_disabled = true; > + dynamic_ibrs = 0; > + spec_ctrl_flush_all_cpus(MSR_IA32_SPEC_CTRL, > + SPEC_CTRL_FEATURE_DISABLE_IBRS); > + > + } else if (enable == IBRS_ENABLED) { > + /* enable IBRS usage in kernel */ > + ibrs_admin_disabled = false; > + dynamic_ibrs = 1; > + > + } else if (enable == IBRS_ENABLED_USER) { > + /* enable IBRS all the time in both userspace and kernel */ > + ibrs_admin_disabled = false; > + dynamic_ibrs = 0; > + spec_ctrl_flush_all_cpus(MSR_IA32_SPEC_CTRL, > + SPEC_CTRL_FEATURE_ENABLE_IBRS);
So what about the CPUs that were offline when you did this? > + } > + > + ibrs_enabled = enable; > + > + mutex_unlock(&spec_ctrl_mutex); > + return count; > +}