use_temporary

/*
 * Using a temporary mm allows to set temporary mappings that are not accessible
 * by other CPUs. Such mappings are needed to perform sensitive memory writes
 * that override the kernel memory protections (e.g., W^X), without exposing the
 * temporary page-table mappings that are required for these write operations to
 * other CPUs. Using a temporary mm also allows to avoid TLB shootdowns when the
 * mapping is torn down.
 *
 * Context: The temporary mm needs to be used exclusively by a single core. To
 *          harden security IRQs must be disabled while the temporary mm is
 *          loaded, thereby preventing interrupt handler bugs from overriding
 *          the kernel memory protection.
 */
static inline temp_mm_state_t use_temporary_mm(struct mm_struct *mm)
{
    temp_mm_state_t temp_state;
 
    lockdep_assert_irqs_disabled();
    temp_state.mm = this_cpu_read(cpu_tlbstate.loaded_mm);
    switch_mm_irqs_off(NULL, mm, current);
 
    /*
     * If breakpoints are enabled, disable them while the temporary mm is
     * used. Userspace might set up watchpoints on addresses that are used
     * in the temporary mm, which would lead to wrong signals being sent or
     * crashes.
     *
     * Note that breakpoints are not disabled selectively, which also causes
     * kernel breakpoints (e.g., perf's) to be disabled. This might be
     * undesirable, but still seems reasonable as the code that runs in the
     * temporary mm should be short.
     */
    if (hw_breakpoint_active())
        hw_breakpoint_disable();
 
    return temp_state;
}
函数源码
