/*P:800
   * Interrupts (traps) are complicated enough to earn their own file.

   * There are three classes of interrupts:
   *
   * 1) Real hardware interrupts which occur while we're running the Guest,
   * 2) Interrupts for virtual devices attached to the Guest, and
   * 3) Traps and faults from the Guest.
   *
   * Real hardware interrupts must be delivered to the Host, not the Guest.
   * Virtual interrupts must be delivered to the Guest, but we make them look
   * just like real hardware would deliver them.  Traps from the Guest can be set
   * up to go directly back into the Guest, but sometimes the Host wants to see
   * them first, so we also have a way of "reflecting" them into the Guest as if

   * they had been delivered to it directly.
  :*/

  #include <linux/uaccess.h>

  #include <linux/interrupt.h>
  #include <linux/module.h>

  #include <linux/sched.h>

  #include "lg.h"

  /* Allow Guests to use a non-128 (ie. non-Linux) syscall trap. */
  static unsigned int syscall_vector = SYSCALL_VECTOR;
  module_param(syscall_vector, uint, 0444);

  /* The address of the interrupt handler is split into two bits: */

  static unsigned long idt_address(u32 lo, u32 hi)
  {
  	return (lo & 0x0000FFFF) | (hi & 0xFFFF0000);
  }

  /*
   * The "type" of the interrupt handler is a 4 bit field: we only support a
   * couple of types.
   */

  static int idt_type(u32 lo, u32 hi)
  {
  	return (hi >> 8) & 0xF;
  }

  /* An IDT entry can't be used unless the "present" bit is set. */

  static bool idt_present(u32 lo, u32 hi)

  {
  	return (hi & 0x8000);
  }

  /*
   * We need a helper to "push" a value onto the Guest's stack, since that's a
   * big part of what delivering an interrupt does.
   */

  static void push_guest_stack(struct lg_cpu *cpu, unsigned long *gstack, u32 val)

  {

  	/* Stack grows upwards: move stack then write value. */

  	*gstack -= 4;

  	lgwrite(cpu, *gstack, u32, val);

  }

  /*H:210
   * The set_guest_interrupt() routine actually delivers the interrupt or

   * trap.  The mechanics of delivering traps and interrupts to the Guest are the
   * same, except some traps have an "error code" which gets pushed onto the
   * stack as well: the caller tells us if this is one.
   *
   * "lo" and "hi" are the two parts of the Interrupt Descriptor Table for this
   * interrupt or trap.  It's split into two parts for traditional reasons: gcc
   * on i386 used to be frightened by 64 bit numbers.
   *
   * We set up the stack just like the CPU does for a real interrupt, so it's
   * identical for the Guest (and the standard "iret" instruction will undo

   * it).
   */

  static void set_guest_interrupt(struct lg_cpu *cpu, u32 lo, u32 hi,
  				bool has_err)

  {

  	unsigned long gstack, origstack;

  	u32 eflags, ss, irq_enable;

  	unsigned long virtstack;

  	/*
  	 * There are two cases for interrupts: one where the Guest is already

  	 * in the kernel, and a more complex one where the Guest is in

  	 * userspace.  We check the privilege level to find out.
  	 */

  	if ((cpu->regs->ss&0x3) != GUEST_PL) {

  		/*
  		 * The Guest told us their kernel stack with the SET_STACK
  		 * hypercall: both the virtual address and the segment.
  		 */

  		virtstack = cpu->esp1;
  		ss = cpu->ss1;

  		origstack = gstack = guest_pa(cpu, virtstack);

  		/*
  		 * We push the old stack segment and pointer onto the new

  		 * stack: when the Guest does an "iret" back from the interrupt
  		 * handler the CPU will notice they're dropping privilege

  		 * levels and expect these here.
  		 */

  		push_guest_stack(cpu, &gstack, cpu->regs->ss);
  		push_guest_stack(cpu, &gstack, cpu->regs->esp);

  	} else {

  		/* We're staying on the same Guest (kernel) stack. */

  		virtstack = cpu->regs->esp;
  		ss = cpu->regs->ss;

  		origstack = gstack = guest_pa(cpu, virtstack);

  	}

  	/*
  	 * Remember that we never let the Guest actually disable interrupts, so

  	 * the "Interrupt Flag" bit is always set.  We copy that bit from the

  	 * Guest's "irq_enabled" field into the eflags word: we saw the Guest

  	 * copy it back in "lguest_iret".
  	 */

  	eflags = cpu->regs->eflags;

  	if (get_user(irq_enable, &cpu->lg->lguest_data->irq_enabled) == 0

  	    && !(irq_enable & X86_EFLAGS_IF))
  		eflags &= ~X86_EFLAGS_IF;

  	/*
  	 * An interrupt is expected to push three things on the stack: the old

  	 * "eflags" word, the old code segment, and the old instruction

  	 * pointer.
  	 */

  	push_guest_stack(cpu, &gstack, eflags);
  	push_guest_stack(cpu, &gstack, cpu->regs->cs);
  	push_guest_stack(cpu, &gstack, cpu->regs->eip);

  	/* For the six traps which supply an error code, we push that, too. */

  	if (has_err)

  		push_guest_stack(cpu, &gstack, cpu->regs->errcode);

  	/*
  	 * Now we've pushed all the old state, we change the stack, the code
  	 * segment and the address to execute.
  	 */

  	cpu->regs->ss = ss;
  	cpu->regs->esp = virtstack + (gstack - origstack);
  	cpu->regs->cs = (__KERNEL_CS|GUEST_PL);
  	cpu->regs->eip = idt_address(lo, hi);

  	/*
  	 * There are two kinds of interrupt handlers: 0xE is an "interrupt
  	 * gate" which expects interrupts to be disabled on entry.
  	 */

  	if (idt_type(lo, hi) == 0xE)

  		if (put_user(0, &cpu->lg->lguest_data->irq_enabled))
  			kill_guest(cpu, "Disabling interrupts");

  }

  /*H:205

   * Virtual Interrupts.
   *

   * interrupt_pending() returns the first pending interrupt which isn't blocked
   * by the Guest.  It is called before every entry to the Guest, and just before

   * we go to sleep when the Guest has halted itself.
   */

  unsigned int interrupt_pending(struct lg_cpu *cpu, bool *more)

  {
  	unsigned int irq;
  	DECLARE_BITMAP(blk, LGUEST_IRQS);

  	/* If the Guest hasn't even initialized yet, we can do nothing. */

  	if (!cpu->lg->lguest_data)

  		return LGUEST_IRQS;

  	/*
  	 * Take our "irqs_pending" array and remove any interrupts the Guest
  	 * wants blocked: the result ends up in "blk".
  	 */

  	if (copy_from_user(&blk, cpu->lg->lguest_data->blocked_interrupts,

  			   sizeof(blk)))

  		return LGUEST_IRQS;

  	bitmap_andnot(blk, cpu->irqs_pending, blk, LGUEST_IRQS);

  	/* Find the first interrupt. */

  	irq = find_first_bit(blk, LGUEST_IRQS);

  	*more = find_next_bit(blk, LGUEST_IRQS, irq+1);

  
  	return irq;
  }

  /*
   * This actually diverts the Guest to running an interrupt handler, once an
   * interrupt has been identified by interrupt_pending().
   */

  void try_deliver_interrupt(struct lg_cpu *cpu, unsigned int irq, bool more)

  {
  	struct desc_struct *idt;
  
  	BUG_ON(irq >= LGUEST_IRQS);

  	/*
  	 * They may be in the middle of an iret, where they asked us never to
  	 * deliver interrupts.
  	 */

  	if (cpu->regs->eip >= cpu->lg->noirq_start &&
  	   (cpu->regs->eip < cpu->lg->noirq_end))

  		return;

  	/* If they're halted, interrupts restart them. */

  	if (cpu->halted) {

  		/* Re-enable interrupts. */

  		if (put_user(X86_EFLAGS_IF, &cpu->lg->lguest_data->irq_enabled))
  			kill_guest(cpu, "Re-enabling interrupts");

  		cpu->halted = 0;

  	} else {

  		/* Otherwise we check if they have interrupts disabled. */

  		u32 irq_enabled;

  		if (get_user(irq_enabled, &cpu->lg->lguest_data->irq_enabled))

  			irq_enabled = 0;

  		if (!irq_enabled) {
  			/* Make sure they know an IRQ is pending. */
  			put_user(X86_EFLAGS_IF,
  				 &cpu->lg->lguest_data->irq_pending);

  			return;

  		}

  	}

  	/*
  	 * Look at the IDT entry the Guest gave us for this interrupt.  The

  	 * first 32 (FIRST_EXTERNAL_VECTOR) entries are for traps, so we skip

  	 * over them.
  	 */

  	idt = &cpu->arch.idt[FIRST_EXTERNAL_VECTOR+irq];

  	/* If they don't have a handler (yet?), we just ignore it */

  	if (idt_present(idt->a, idt->b)) {

  		/* OK, mark it no longer pending and deliver it. */

  		clear_bit(irq, cpu->irqs_pending);

  		/*
  		 * set_guest_interrupt() takes the interrupt descriptor and a

  		 * flag to say whether this interrupt pushes an error code onto

  		 * the stack as well: virtual interrupts never do.
  		 */

  		set_guest_interrupt(cpu, idt->a, idt->b, false);

  	}

  	/*
  	 * Every time we deliver an interrupt, we update the timestamp in the

  	 * Guest's lguest_data struct.  It would be better for the Guest if we
  	 * did this more often, but it can actually be quite slow: doing it
  	 * here is a compromise which means at least it gets updated every

  	 * timer interrupt.
  	 */

  	write_timestamp(cpu);

  	/*
  	 * If there are no other interrupts we want to deliver, clear
  	 * the pending flag.
  	 */

  	if (!more)
  		put_user(0, &cpu->lg->lguest_data->irq_pending);

  }

  
  /* And this is the routine when we want to set an interrupt for the Guest. */
  void set_interrupt(struct lg_cpu *cpu, unsigned int irq)
  {

  	/*
  	 * Next time the Guest runs, the core code will see if it can deliver
  	 * this interrupt.
  	 */

  	set_bit(irq, cpu->irqs_pending);

  	/*
  	 * Make sure it sees it; it might be asleep (eg. halted), or running
  	 * the Guest right now, in which case kick_process() will knock it out.
  	 */

  	if (!wake_up_process(cpu->tsk))
  		kick_process(cpu->tsk);
  }

  /*:*/

  /*
   * Linux uses trap 128 for system calls.  Plan9 uses 64, and Ron Minnich sent

   * me a patch, so we support that too.  It'd be a big step for lguest if half
   * the Plan 9 user base were to start using it.
   *
   * Actually now I think of it, it's possible that Ron *is* half the Plan 9

   * userbase.  Oh well.
   */

  static bool could_be_syscall(unsigned int num)
  {
  	/* Normal Linux SYSCALL_VECTOR or reserved vector? */
  	return num == SYSCALL_VECTOR || num == syscall_vector;
  }
  
  /* The syscall vector it wants must be unused by Host. */
  bool check_syscall_vector(struct lguest *lg)
  {
  	u32 vector;
  
  	if (get_user(vector, &lg->lguest_data->syscall_vec))
  		return false;
  
  	return could_be_syscall(vector);
  }
  
  int init_interrupts(void)
  {
  	/* If they want some strange system call vector, reserve it now */

  	if (syscall_vector != SYSCALL_VECTOR) {
  		if (test_bit(syscall_vector, used_vectors) ||
  		    vector_used_by_percpu_irq(syscall_vector)) {
  			printk(KERN_ERR "lg: couldn't reserve syscall %u
  ",
  				 syscall_vector);
  			return -EBUSY;
  		}
  		set_bit(syscall_vector, used_vectors);

  	}

  	return 0;
  }
  
  void free_interrupts(void)
  {
  	if (syscall_vector != SYSCALL_VECTOR)
  		clear_bit(syscall_vector, used_vectors);
  }

  /*H:220
   * Now we've got the routines to deliver interrupts, delivering traps like

   * page fault is easy.  The only trick is that Intel decided that some traps

   * should have error codes:
   */

  static bool has_err(unsigned int trap)

  {
  	return (trap == 8 || (trap >= 10 && trap <= 14) || trap == 17);
  }

  /* deliver_trap() returns true if it could deliver the trap. */

  bool deliver_trap(struct lg_cpu *cpu, unsigned int num)

  {

  	/*
  	 * Trap numbers are always 8 bit, but we set an impossible trap number
  	 * for traps inside the Switcher, so check that here.
  	 */

  	if (num >= ARRAY_SIZE(cpu->arch.idt))

  		return false;

  	/*
  	 * Early on the Guest hasn't set the IDT entries (or maybe it put a
  	 * bogus one in): if we fail here, the Guest will be killed.
  	 */

  	if (!idt_present(cpu->arch.idt[num].a, cpu->arch.idt[num].b))

  		return false;

  	set_guest_interrupt(cpu, cpu->arch.idt[num].a,
  			    cpu->arch.idt[num].b, has_err(num));

  	return true;

  }

  /*H:250
   * Here's the hard part: returning to the Host every time a trap happens

   * and then calling deliver_trap() and re-entering the Guest is slow.

   * Particularly because Guest userspace system calls are traps (usually trap
   * 128).

   *
   * So we'd like to set up the IDT to tell the CPU to deliver traps directly
   * into the Guest.  This is possible, but the complexities cause the size of
   * this file to double!  However, 150 lines of code is worth writing for taking
   * system calls down from 1750ns to 270ns.  Plus, if lguest didn't do it, all

   * the other hypervisors would beat it up at lunchtime.

   *

   * This routine indicates if a particular trap number could be delivered

   * directly.
   */

  static bool direct_trap(unsigned int num)

  {

  	/*
  	 * Hardware interrupts don't go to the Guest at all (except system
  	 * call).
  	 */

  	if (num >= FIRST_EXTERNAL_VECTOR && !could_be_syscall(num))

  		return false;

  	/*
  	 * The Host needs to see page faults (for shadow paging and to save the

  	 * fault address), general protection faults (in/out emulation) and

  	 * device not available (TS handling) and of course, the hypercall trap.

  	 */

  	return num != 14 && num != 13 && num != 7 && num != LGUEST_TRAP_ENTRY;

  }

  /*:*/

  /*M:005
   * The Guest has the ability to turn its interrupt gates into trap gates,

   * if it is careful.  The Host will let trap gates can go directly to the
   * Guest, but the Guest needs the interrupts atomically disabled for an
   * interrupt gate.  It can do this by pointing the trap gate at instructions

   * within noirq_start and noirq_end, where it can safely disable interrupts.
   */

  /*M:006
   * The Guests do not use the sysenter (fast system call) instruction,

   * because it's hardcoded to enter privilege level 0 and so can't go direct.
   * It's about twice as fast as the older "int 0x80" system call, so it might
   * still be worthwhile to handle it in the Switcher and lcall down to the
   * Guest.  The sysenter semantics are hairy tho: search for that keyword in

   * entry.S
  :*/

  /*H:260
   * When we make traps go directly into the Guest, we need to make sure

   * the kernel stack is valid (ie. mapped in the page tables).  Otherwise, the
   * CPU trying to deliver the trap will fault while trying to push the interrupt
   * words on the stack: this is called a double fault, and it forces us to kill
   * the Guest.
   *

   * Which is deeply unfair, because (literally!) it wasn't the Guests' fault.
   */

  void pin_stack_pages(struct lg_cpu *cpu)

  {
  	unsigned int i;

  	/*
  	 * Depending on the CONFIG_4KSTACKS option, the Guest can have one or
  	 * two pages of stack space.
  	 */

  	for (i = 0; i < cpu->lg->stack_pages; i++)

  		/*
  		 * The stack grows *upwards*, so the address we're given is the

  		 * start of the page after the kernel stack.  Subtract one to
  		 * get back onto the first stack page, and keep subtracting to

  		 * get to the rest of the stack pages.
  		 */

  		pin_page(cpu, cpu->esp1 - 1 - i * PAGE_SIZE);

  }

  /*
   * Direct traps also mean that we need to know whenever the Guest wants to use

   * a different kernel stack, so we can change the guest TSS to use that
   * stack.  The TSS entries expect a virtual address, so unlike most addresses

   * the Guest gives us, the "esp" (stack pointer) value here is virtual, not
   * physical.
   *
   * In Linux each process has its own kernel stack, so this happens a lot: we

   * change stacks on each context switch.
   */

  void guest_set_stack(struct lg_cpu *cpu, u32 seg, u32 esp, unsigned int pages)

  {

  	/*
  	 * You're not allowed a stack segment with privilege level 0: bad Guest!
  	 */

  	if ((seg & 0x3) != GUEST_PL)

  		kill_guest(cpu, "bad stack segment %i", seg);

  	/* We only expect one or two stack pages. */

  	if (pages > 2)

  		kill_guest(cpu, "bad stack pages %u", pages);

  	/* Save where the stack is, and how many pages */

  	cpu->ss1 = seg;
  	cpu->esp1 = esp;
  	cpu->lg->stack_pages = pages;

  	/* Make sure the new stack pages are mapped */

  	pin_stack_pages(cpu);

  }

  /*
   * All this reference to mapping stacks leads us neatly into the other complex
   * part of the Host: page table handling.
   */

  /*H:235
   * This is the routine which actually checks the Guest's IDT entry and
   * transfers it into the entry in "struct lguest":
   */

  static void set_trap(struct lg_cpu *cpu, struct desc_struct *trap,

  		     unsigned int num, u32 lo, u32 hi)
  {
  	u8 type = idt_type(lo, hi);

  	/* We zero-out a not-present entry */

  	if (!idt_present(lo, hi)) {
  		trap->a = trap->b = 0;
  		return;
  	}

  	/* We only support interrupt and trap gates. */

  	if (type != 0xE && type != 0xF)

  		kill_guest(cpu, "bad IDT type %i", type);

  	/*
  	 * We only copy the handler address, present bit, privilege level and

  	 * type.  The privilege level controls where the trap can be triggered
  	 * manually with an "int" instruction.  This is usually GUEST_PL,

  	 * except for system calls which userspace can use.
  	 */

  	trap->a = ((__KERNEL_CS|GUEST_PL)<<16) | (lo&0x0000FFFF);
  	trap->b = (hi&0xFFFFEF00);
  }

  /*H:230
   * While we're here, dealing with delivering traps and interrupts to the

   * Guest, we might as well complete the picture: how the Guest tells us where
   * it wants them to go.  This would be simple, except making traps fast
   * requires some tricks.
   *
   * We saw the Guest setting Interrupt Descriptor Table (IDT) entries with the

   * LHCALL_LOAD_IDT_ENTRY hypercall before: that comes here.
   */

  void load_guest_idt_entry(struct lg_cpu *cpu, unsigned int num, u32 lo, u32 hi)

  {

  	/*
  	 * Guest never handles: NMI, doublefault, spurious interrupt or
  	 * hypercall.  We ignore when it tries to set them.
  	 */

  	if (num == 2 || num == 8 || num == 15 || num == LGUEST_TRAP_ENTRY)
  		return;

  	/*
  	 * Mark the IDT as changed: next time the Guest runs we'll know we have
  	 * to copy this again.
  	 */

  	cpu->changed |= CHANGED_IDT;

  	/* Check that the Guest doesn't try to step outside the bounds. */

  	if (num >= ARRAY_SIZE(cpu->arch.idt))

  		kill_guest(cpu, "Setting idt entry %u", num);

  	else

  		set_trap(cpu, &cpu->arch.idt[num], num, lo, hi);

  }

  /*
   * The default entry for each interrupt points into the Switcher routines which

   * simply return to the Host.  The run_guest() loop will then call

   * deliver_trap() to bounce it back into the Guest.
   */

  static void default_idt_entry(struct desc_struct *idt,
  			      int trap,

  			      const unsigned long handler,
  			      const struct desc_struct *base)

  {

  	/* A present interrupt gate. */

  	u32 flags = 0x8e00;

  	/*
  	 * Set the privilege level on the entry for the hypercall: this allows
  	 * the Guest to use the "int" instruction to trigger it.
  	 */

  	if (trap == LGUEST_TRAP_ENTRY)
  		flags |= (GUEST_PL << 13);

  	else if (base)

  		/*
  		 * Copy privilege level from what Guest asked for.  This allows
  		 * debug (int 3) traps from Guest userspace, for example.
  		 */

  		flags |= (base->b & 0x6000);

  	/* Now pack it into the IDT entry in its weird format. */

  	idt->a = (LGUEST_CS<<16) | (handler&0x0000FFFF);
  	idt->b = (handler&0xFFFF0000) | flags;
  }

  /* When the Guest first starts, we put default entries into the IDT. */

  void setup_default_idt_entries(struct lguest_ro_state *state,
  			       const unsigned long *def)
  {
  	unsigned int i;
  
  	for (i = 0; i < ARRAY_SIZE(state->guest_idt); i++)

  		default_idt_entry(&state->guest_idt[i], i, def[i], NULL);

  }

  /*H:240
   * We don't use the IDT entries in the "struct lguest" directly, instead

   * we copy them into the IDT which we've set up for Guests on this CPU, just

   * before we run the Guest.  This routine does that copy.
   */

  void copy_traps(const struct lg_cpu *cpu, struct desc_struct *idt,

  		const unsigned long *def)
  {
  	unsigned int i;

  	/*
  	 * We can simply copy the direct traps, otherwise we use the default
  	 * ones in the Switcher: they will return to the Host.
  	 */

  	for (i = 0; i < ARRAY_SIZE(cpu->arch.idt); i++) {

  		const struct desc_struct *gidt = &cpu->arch.idt[i];

  		/* If no Guest can ever override this trap, leave it alone. */
  		if (!direct_trap(i))
  			continue;

  		/*
  		 * Only trap gates (type 15) can go direct to the Guest.

  		 * Interrupt gates (type 14) disable interrupts as they are
  		 * entered, which we never let the Guest do.  Not present

  		 * entries (type 0x0) also can't go direct, of course.
  		 *
  		 * If it can't go direct, we still need to copy the priv. level:
  		 * they might want to give userspace access to a software

  		 * interrupt.
  		 */

  		if (idt_type(gidt->a, gidt->b) == 0xF)
  			idt[i] = *gidt;

  		else

  			default_idt_entry(&idt[i], i, def[i], gidt);

  	}

  }

  /*H:200
   * The Guest Clock.
   *
   * There are two sources of virtual interrupts.  We saw one in lguest_user.c:
   * the Launcher sending interrupts for virtual devices.  The other is the Guest
   * timer interrupt.
   *
   * The Guest uses the LHCALL_SET_CLOCKEVENT hypercall to tell us how long to
   * the next timer interrupt (in nanoseconds).  We use the high-resolution timer
   * infrastructure to set a callback at that time.
   *

   * 0 means "turn off the clock".
   */

  void guest_set_clockevent(struct lg_cpu *cpu, unsigned long delta)

  {
  	ktime_t expires;
  
  	if (unlikely(delta == 0)) {
  		/* Clock event device is shutting down. */

  		hrtimer_cancel(&cpu->hrt);

  		return;
  	}

  	/*
  	 * We use wallclock time here, so the Guest might not be running for

  	 * all the time between now and the timer interrupt it asked for.  This

  	 * is almost always the right thing to do.
  	 */

  	expires = ktime_add_ns(ktime_get_real(), delta);

  	hrtimer_start(&cpu->hrt, expires, HRTIMER_MODE_ABS);

  }

  /* This is the function called when the Guest's timer expires. */

  static enum hrtimer_restart clockdev_fn(struct hrtimer *timer)
  {

  	struct lg_cpu *cpu = container_of(timer, struct lg_cpu, hrt);

  	/* Remember the first interrupt is the timer interrupt. */

  	set_interrupt(cpu, 0);

  	return HRTIMER_NORESTART;
  }

  /* This sets up the timer for this Guest. */

  void init_clockdev(struct lg_cpu *cpu)

  {

  	hrtimer_init(&cpu->hrt, CLOCK_REALTIME, HRTIMER_MODE_ABS);
  	cpu->hrt.function = clockdev_fn;

  }