/*
 *  Copyright (C) 1995  Linus Torvalds
 *
 *  Pentium III FXSR, SSE support
 *      Gareth Hughes <gareth@valinux.com>, May 2000
 */

/*
 * This file handles the architecture-dependent parts of process handling..
 */

#include <linux/stackprotector.h>
#include <linux/cpu.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/elfcore.h>
#include <linux/smp.h>
#include <linux/stddef.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/user.h>
#include <linux/interrupt.h>
#include <linux/delay.h>
#include <linux/reboot.h>
#include <linux/init.h>
#include <linux/mc146818rtc.h>
#include <linux/module.h>
#include <linux/kallsyms.h>
#include <linux/ptrace.h>
#include <linux/personality.h>
#include <linux/tick.h>
#include <linux/percpu.h>
#include <linux/prctl.h>
#include <linux/ftrace.h>
#include <linux/uaccess.h>
#include <linux/io.h>
#include <linux/kdebug.h>
#include <linux/cpuidle.h>

#include <asm/pgtable.h>
#include <asm/system.h>
#include <asm/ldt.h>
#include <asm/processor.h>
#include <asm/i387.h>
#include <asm/desc.h>
#ifdef CONFIG_MATH_EMULATION
#include <asm/math_emu.h>
#endif

#include <linux/err.h>

#include <asm/tlbflush.h>
#include <asm/cpu.h>
#include <asm/idle.h>
#include <asm/syscalls.h>
#include <asm/debugreg.h>
#include <asm/nmi.h>

asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");

/*
 * Return saved PC of a blocked thread.
 */
unsigned long thread_saved_pc(struct task_struct *tsk)
{
        return ((unsigned long *)tsk->thread.sp)[3];
}

#ifndef CONFIG_SMP
static inline void play_dead(void)
{
        BUG();
}
#endif

/*
 * The idle thread. There's no useful work to be
 * done, so just try to conserve power and have a
 * low exit latency (ie sit in a loop waiting for
 * somebody to say that they'd like to reschedule)
 */
void cpu_idle(void)
{
        int cpu = smp_processor_id();

        /*
         * If we're the non-boot CPU, nothing set the stack canary up
         * for us.  CPU0 already has it initialized but no harm in
         * doing it again.  This is a good place for updating it, as
         * we wont ever return from this function (so the invalid
         * canaries already on the stack wont ever trigger).
         */
        boot_init_stack_canary();

        current_thread_info()->status |= TS_POLLING;

        /* endless idle loop with no priority at all */
        while (1) {
                tick_nohz_stop_sched_tick(1);
                while (!need_resched()) {

                        check_pgt_cache();
                        rmb();

                        if (cpu_is_offline(cpu))
                                play_dead();

                        local_touch_nmi();
                        local_irq_disable();
                        /* Don't trace irqs off for idle */
                        stop_critical_timings();
                        if (cpuidle_idle_call())
                                pm_idle();
                        start_critical_timings();
                }
                tick_nohz_restart_sched_tick();
                preempt_enable_no_resched();
                schedule();
                preempt_disable();
        }
}

void __show_regs(struct pt_regs *regs, int all)
{
        unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L;
        unsigned long d0, d1, d2, d3, d6, d7;
        unsigned long sp;
        unsigned short ss, gs;

        if (user_mode_vm(regs)) {
                sp = regs->sp;
                ss = regs->ss & 0xffff;
                gs = get_user_gs(regs);
        } else {
                sp = kernel_stack_pointer(regs);
                savesegment(ss, ss);
                savesegment(gs, gs);
        }

        show_regs_common();

        printk(KERN_DEFAULT "EIP: %04x:[<%08lx>] EFLAGS: %08lx CPU: %d\n",
                        (u16)regs->cs, regs->ip, regs->flags,
                        smp_processor_id());
        print_symbol("EIP is at %s\n", regs->ip);

        printk(KERN_DEFAULT "EAX: %08lx EBX: %08lx ECX: %08lx EDX: %08lx\n",
                regs->ax, regs->bx, regs->cx, regs->dx);
        printk(KERN_DEFAULT "ESI: %08lx EDI: %08lx EBP: %08lx ESP: %08lx\n",
                regs->si, regs->di, regs->bp, sp);
        printk(KERN_DEFAULT " DS: %04x ES: %04x FS: %04x GS: %04x SS: %04x\n",
               (u16)regs->ds, (u16)regs->es, (u16)regs->fs, gs, ss);

        if (!all)
                return;

        cr0 = read_cr0();
        cr2 = read_cr2();
        cr3 = read_cr3();
        cr4 = read_cr4_safe();
        printk(KERN_DEFAULT "CR0: %08lx CR2: %08lx CR3: %08lx CR4: %08lx\n",
                        cr0, cr2, cr3, cr4);

        get_debugreg(d0, 0);
        get_debugreg(d1, 1);
        get_debugreg(d2, 2);
        get_debugreg(d3, 3);
        printk(KERN_DEFAULT "DR0: %08lx DR1: %08lx DR2: %08lx DR3: %08lx\n",
                        d0, d1, d2, d3);

        get_debugreg(d6, 6);
        get_debugreg(d7, 7);
        printk(KERN_DEFAULT "DR6: %08lx DR7: %08lx\n",
                        d6, d7);
}

void release_thread(struct task_struct *dead_task)
{
        BUG_ON(dead_task->mm);
        release_vm86_irqs(dead_task);
}

/*
 * This gets called before we allocate a new thread and copy
 * the current task into it.
 */
void prepare_to_copy(struct task_struct *tsk)
{
        unlazy_fpu(tsk);
}

int copy_thread(unsigned long clone_flags, unsigned long sp,
        unsigned long unused,
        struct task_struct *p, struct pt_regs *regs)
{
        struct pt_regs *childregs;
        struct task_struct *tsk;
        int err;

        childregs = task_pt_regs(p);
        *childregs = *regs;
        childregs->ax = 0;
        childregs->sp = sp;

        p->thread.sp = (unsigned long) childregs;
        p->thread.sp0 = (unsigned long) (childregs+1);

        p->thread.ip = (unsigned long) ret_from_fork;

        task_user_gs(p) = get_user_gs(regs);

        p->thread.io_bitmap_ptr = NULL;
        tsk = current;
        err = -ENOMEM;

        memset(p->thread.ptrace_bps, 0, sizeof(p->thread.ptrace_bps));

        if (unlikely(test_tsk_thread_flag(tsk, TIF_IO_BITMAP))) {
                p->thread.io_bitmap_ptr = kmemdup(tsk->thread.io_bitmap_ptr,
                                                IO_BITMAP_BYTES, GFP_KERNEL);
                if (!p->thread.io_bitmap_ptr) {
                        p->thread.io_bitmap_max = 0;
                        return -ENOMEM;
                }
                set_tsk_thread_flag(p, TIF_IO_BITMAP);
        }

        err = 0;

        /*
         * Set a new TLS for the child thread?
         */
        if (clone_flags & CLONE_SETTLS)
                err = do_set_thread_area(p, -1,
                        (struct user_desc __user *)childregs->si, 0);

        if (err && p->thread.io_bitmap_ptr) {
                kfree(p->thread.io_bitmap_ptr);
                p->thread.io_bitmap_max = 0;
        }
        return err;
}

void
start_thread(struct pt_regs *regs, unsigned long new_ip, unsigned long new_sp)
{
        set_user_gs(regs, 0);
        regs->fs                = 0;
        regs->ds                = __USER_DS;
        regs->es                = __USER_DS;
        regs->ss                = __USER_DS;
        regs->cs                = __USER_CS;
        regs->ip                = new_ip;
        regs->sp                = new_sp;
        /*
         * Free the old FP and other extended state
         */
        free_thread_xstate(current);
}
EXPORT_SYMBOL_GPL(start_thread);


/*
 *      switch_to(x,y) should switch tasks from x to y.
 *
 * We fsave/fwait so that an exception goes off at the right time
 * (as a call from the fsave or fwait in effect) rather than to
 * the wrong process. Lazy FP saving no longer makes any sense
 * with modern CPU's, and this simplifies a lot of things (SMP
 * and UP become the same).
 *
 * NOTE! We used to use the x86 hardware context switching. The
 * reason for not using it any more becomes apparent when you
 * try to recover gracefully from saved state that is no longer
 * valid (stale segment register values in particular). With the
 * hardware task-switch, there is no way to fix up bad state in
 * a reasonable manner.
 *
 * The fact that Intel documents the hardware task-switching to
 * be slow is a fairly red herring - this code is not noticeably
 * faster. However, there _is_ some room for improvement here,
 * so the performance issues may eventually be a valid point.
 * More important, however, is the fact that this allows us much
 * more flexibility.
 *
 * The return value (in %ax) will be the "prev" task after
 * the task-switch, and shows up in ret_from_fork in entry.S,
 * for example.
 */
__notrace_funcgraph struct task_struct *
__switch_to(struct task_struct *prev_p, struct task_struct *next_p)
{
        struct thread_struct *prev = &prev_p->thread,
                                 *next = &next_p->thread;
        int cpu = smp_processor_id();
        struct tss_struct *tss = &per_cpu(init_tss, cpu);
        bool preload_fpu;

        /* never put a printk in __switch_to... printk() calls wake_up*() indirectly */

        /*
         * If the task has used fpu the last 5 timeslices, just do a full
         * restore of the math state immediately to avoid the trap; the
         * chances of needing FPU soon are obviously high now
         */
        preload_fpu = tsk_used_math(next_p) && next_p->fpu_counter > 5;

        __unlazy_fpu(prev_p);

        /* we're going to use this soon, after a few expensive things */
        if (preload_fpu)
                prefetch(next->fpu.state);

        /*
         * Reload esp0.
         */
        load_sp0(tss, next);

        /*
         * Save away %gs. No need to save %fs, as it was saved on the
         * stack on entry.  No need to save %es and %ds, as those are
         * always kernel segments while inside the kernel.  Doing this
         * before setting the new TLS descriptors avoids the situation
         * where we temporarily have non-reloadable segments in %fs
         * and %gs.  This could be an issue if the NMI handler ever
         * used %fs or %gs (it does not today), or if the kernel is
         * running inside of a hypervisor layer.
         */
        lazy_save_gs(prev->gs);

        /*
         * Load the per-thread Thread-Local Storage descriptor.
         */
        load_TLS(next, cpu);

        /*
         * Restore IOPL if needed.  In normal use, the flags restore
         * in the switch assembly will handle this.  But if the kernel
         * is running virtualized at a non-zero CPL, the popf will
         * not restore flags, so it must be done in a separate step.
         */
        if (get_kernel_rpl() && unlikely(prev->iopl != next->iopl))
                set_iopl_mask(next->iopl);

        /*
         * Now maybe handle debug registers and/or IO bitmaps
         */
        if (unlikely(task_thread_info(prev_p)->flags & _TIF_WORK_CTXSW_PREV ||
                     task_thread_info(next_p)->flags & _TIF_WORK_CTXSW_NEXT))
                __switch_to_xtra(prev_p, next_p, tss);

        /* If we're going to preload the fpu context, make sure clts
           is run while we're batching the cpu state updates. */
        if (preload_fpu)
                clts();

        /*
         * Leave lazy mode, flushing any hypercalls made here.
         * This must be done before restoring TLS segments so
         * the GDT and LDT are properly updated, and must be
         * done before math_state_restore, so the TS bit is up
         * to date.
         */
        arch_end_context_switch(next_p);

        if (preload_fpu)
                __math_state_restore();

        /*
         * Restore %gs if needed (which is common)
         */
        if (prev->gs | next->gs)
                lazy_load_gs(next->gs);

        percpu_write(current_task, next_p);

        return prev_p;
}

#define top_esp                (THREAD_SIZE - sizeof(unsigned long))
#define top_ebp                (THREAD_SIZE - 2*sizeof(unsigned long))

unsigned long get_wchan(struct task_struct *p)
{
        unsigned long bp, sp, ip;
        unsigned long stack_page;
        int count = 0;
        if (!p || p == current || p->state == TASK_RUNNING)
                return 0;
        stack_page = (unsigned long)task_stack_page(p);
        sp = p->thread.sp;
        if (!stack_page || sp < stack_page || sp > top_esp+stack_page)
                return 0;
        /* include/asm-i386/system.h:switch_to() pushes bp last. */
        bp = *(unsigned long *) sp;
        do {
                if (bp < stack_page || bp > top_ebp+stack_page)
                        return 0;
                ip = *(unsigned long *) (bp+4);
                if (!in_sched_functions(ip))
                        return ip;
                bp = *(unsigned long *) bp;
        } while (count++ < 16);
        return 0;
}