+/*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 "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 int 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 lguest *lg, unsigned long *gstack, u32 val)
{
+ /* Stack grows upwards: move stack then write value. */
*gstack -= 4;
- lgwrite_u32(lg, *gstack, val);
+ lgwrite(lg, *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 lguest *lg, u32 lo, u32 hi, int has_err)
{
- unsigned long gstack;
+ unsigned long gstack, origstack;
u32 eflags, ss, irq_enable;
+ unsigned long virtstack;
- /* If they want a ring change, we use new stack and push old ss/esp */
+ /* 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 ((lg->regs->ss&0x3) != GUEST_PL) {
- gstack = guest_pa(lg, lg->esp1);
+ /* The Guest told us their kernel stack with the SET_STACK
+ * hypercall: both the virtual address and the segment */
+ virtstack = lg->esp1;
ss = lg->ss1;
+
+ origstack = gstack = guest_pa(lg, 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(lg, &gstack, lg->regs->ss);
push_guest_stack(lg, &gstack, lg->regs->esp);
} else {
- gstack = guest_pa(lg, lg->regs->esp);
+ /* We're staying on the same Guest (kernel) stack. */
+ virtstack = lg->regs->esp;
ss = lg->regs->ss;
+
+ origstack = gstack = guest_pa(lg, virtstack);
}
- /* We use IF bit in eflags to indicate whether irqs were enabled
- (it's always 1, since irqs are enabled when guest is running). */
+ /* 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 = lg->regs->eflags;
if (get_user(irq_enable, &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(lg, &gstack, eflags);
push_guest_stack(lg, &gstack, lg->regs->cs);
push_guest_stack(lg, &gstack, lg->regs->eip);
+ /* For the six traps which supply an error code, we push that, too. */
if (has_err)
push_guest_stack(lg, &gstack, lg->regs->errcode);
- /* Change the real stack so switcher returns to trap handler */
+ /* Now we've pushed all the old state, we change the stack, the code
+ * segment and the address to execute. */
lg->regs->ss = ss;
- lg->regs->esp = gstack + lg->page_offset;
+ lg->regs->esp = virtstack + (gstack - origstack);
lg->regs->cs = (__KERNEL_CS|GUEST_PL);
lg->regs->eip = idt_address(lo, hi);
- /* Disable interrupts for an interrupt gate. */
+ /* 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, &lg->lguest_data->irq_enabled))
kill_guest(lg, "Disabling interrupts");
}
+/*H:205
+ * Virtual Interrupts.
+ *
+ * maybe_do_interrupt() gets called before every entry to the Guest, to see if
+ * we should divert the Guest to running an interrupt handler. */
void maybe_do_interrupt(struct lguest *lg)
{
unsigned int irq;
DECLARE_BITMAP(blk, LGUEST_IRQS);
struct desc_struct *idt;
+ /* If the Guest hasn't even initialized yet, we can do nothing. */
if (!lg->lguest_data)
return;
- /* Mask out any interrupts they have blocked. */
+ /* Take our "irqs_pending" array and remove any interrupts the Guest
+ * wants blocked: the result ends up in "blk". */
if (copy_from_user(&blk, lg->lguest_data->blocked_interrupts,
sizeof(blk)))
return;
bitmap_andnot(blk, lg->irqs_pending, blk, LGUEST_IRQS);
+ /* Find the first interrupt. */
irq = find_first_bit(blk, LGUEST_IRQS);
+ /* None? Nothing to do */
if (irq >= LGUEST_IRQS)
return;
+ /* They may be in the middle of an iret, where they asked us never to
+ * deliver interrupts. */
if (lg->regs->eip >= lg->noirq_start && lg->regs->eip < lg->noirq_end)
return;
- /* If they're halted, we re-enable interrupts. */
+ /* If they're halted, interrupts restart them. */
if (lg->halted) {
/* Re-enable interrupts. */
if (put_user(X86_EFLAGS_IF, &lg->lguest_data->irq_enabled))
kill_guest(lg, "Re-enabling interrupts");
lg->halted = 0;
} else {
- /* Maybe they have interrupts disabled? */
+ /* Otherwise we check if they have interrupts disabled. */
u32 irq_enabled;
if (get_user(irq_enabled, &lg->lguest_data->irq_enabled))
irq_enabled = 0;
return;
}
- idt = &lg->idt[FIRST_EXTERNAL_VECTOR+irq];
+ /* 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 = &lg->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, lg->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(lg, idt->a, idt->b, 0);
}
+
+ /* 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(lg);
+}
+/*:*/
+
+/* 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
+ && test_and_set_bit(syscall_vector, used_vectors)) {
+ printk("lg: couldn't reserve syscall %u\n", syscall_vector);
+ return -EBUSY;
+ }
+ 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 int has_err(unsigned int trap)
{
return (trap == 8 || (trap >= 10 && trap <= 14) || trap == 17);
}
+/* deliver_trap() returns true if it could deliver the trap. */
int deliver_trap(struct lguest *lg, unsigned int num)
{
- u32 lo = lg->idt[num].a, hi = lg->idt[num].b;
+ /* 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(lg->arch.idt))
+ return 0;
- if (!idt_present(lo, hi))
+ /* 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(lg->arch.idt[num].a, lg->arch.idt[num].b))
return 0;
- set_guest_interrupt(lg, lo, hi, has_err(num));
+ set_guest_interrupt(lg, lg->arch.idt[num].a, lg->arch.idt[num].b,
+ has_err(num));
return 1;
}
-static int direct_trap(const struct lguest *lg,
- const struct desc_struct *trap,
- unsigned int num)
+/*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 int direct_trap(unsigned int num)
{
- /* Hardware interrupts don't go to guest (except syscall). */
- if (num >= FIRST_EXTERNAL_VECTOR && num != SYSCALL_VECTOR)
+ /* Hardware interrupts don't go to the Guest at all (except system
+ * call). */
+ if (num >= FIRST_EXTERNAL_VECTOR && !could_be_syscall(num))
return 0;
- /* We intercept page fault (demand shadow paging & cr2 saving)
- protection fault (in/out emulation) and device not
- available (TS handling), and hypercall */
- if (num == 14 || num == 13 || num == 7 || num == LGUEST_TRAP_ENTRY)
- return 0;
-
- /* Interrupt gates (0xE) or not present (0x0) can't go direct. */
- return idt_type(trap->a, trap->b) == 0xF;
+ /* 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 lguest *lg)
{
unsigned int i;
+ /* Depending on the CONFIG_4KSTACKS option, the Guest can have one or
+ * two pages of stack space. */
for (i = 0; i < lg->stack_pages; i++)
- pin_page(lg, lg->esp1 - i * PAGE_SIZE);
+ /* 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(lg, lg->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 IDT entries to use that
+ * stack. The IDT 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 lguest *lg, u32 seg, u32 esp, unsigned int pages)
{
- /* You cannot have a stack segment with priv level 0. */
+ /* You are not allowed have a stack segment with privilege level 0: bad
+ * Guest! */
if ((seg & 0x3) != GUEST_PL)
kill_guest(lg, "bad stack segment %i", seg);
+ /* We only expect one or two stack pages. */
if (pages > 2)
kill_guest(lg, "bad stack pages %u", pages);
+ /* Save where the stack is, and how many pages */
lg->ss1 = seg;
lg->esp1 = esp;
lg->stack_pages = pages;
+ /* Make sure the new stack pages are mapped */
pin_stack_pages(lg);
}
-/* Set up trap in IDT. */
+/* 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 lguest *lg, 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(lg, "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 lguest *lg, unsigned int num, u32 lo, u32 hi)
{
- /* Guest never handles: NMI, doublefault, hypercall, spurious irq. */
+ /* 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. */
lg->changed |= CHANGED_IDT;
- if (num < ARRAY_SIZE(lg->idt))
- set_trap(lg, &lg->idt[num], num, lo, hi);
- else if (num == SYSCALL_VECTOR)
- set_trap(lg, &lg->syscall_idt, num, lo, hi);
+
+ /* Check that the Guest doesn't try to step outside the bounds. */
+ if (num >= ARRAY_SIZE(lg->arch.idt))
+ kill_guest(lg, "Setting idt entry %u", num);
+ else
+ set_trap(lg, &lg->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)
{
+ /* A present interrupt gate. */
u32 flags = 0x8e00;
- /* They can't "int" into any of them except hypercall. */
+ /* 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);
+ /* 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)
{
default_idt_entry(&state->guest_idt[i], i, def[i]);
}
+/*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 lguest *lg, struct desc_struct *idt,
const unsigned long *def)
{
unsigned int i;
- /* All hardware interrupts are same whatever the guest: only the
- * traps might be different. */
- for (i = 0; i < FIRST_EXTERNAL_VECTOR; i++) {
- if (direct_trap(lg, &lg->idt[i], i))
- idt[i] = lg->idt[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(lg->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 (idt_type(lg->arch.idt[i].a, lg->arch.idt[i].b) == 0xF)
+ idt[i] = lg->arch.idt[i];
else
+ /* Reset it to the default. */
default_idt_entry(&idt[i], i, def[i]);
}
- i = SYSCALL_VECTOR;
- if (direct_trap(lg, &lg->syscall_idt, i))
- idt[i] = lg->syscall_idt;
- else
- default_idt_entry(&idt[i], i, def[i]);
}
+/*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 lguest *lg, unsigned long delta)
{
ktime_t expires;
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(&lg->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 lguest *lg = container_of(timer, struct lguest, hrt);
+ /* Remember the first interrupt is the timer interrupt. */
set_bit(0, lg->irqs_pending);
+ /* If the Guest is actually stopped, we need to wake it up. */
if (lg->halted)
wake_up_process(lg->tsk);
return HRTIMER_NORESTART;
}
+/* This sets up the timer for this Guest. */
void init_clockdev(struct lguest *lg)
{
hrtimer_init(&lg->hrt, CLOCK_REALTIME, HRTIMER_MODE_ABS);
projects / linux-2.6-omap-h63xx.git / blobdiff