diff options
Diffstat (limited to 'drivers/lguest/interrupts_and_traps.c')
| -rw-r--r-- | drivers/lguest/interrupts_and_traps.c | 706 |
1 files changed, 0 insertions, 706 deletions
diff --git a/drivers/lguest/interrupts_and_traps.c b/drivers/lguest/interrupts_and_traps.c deleted file mode 100644 index 67392b6ab845..000000000000 --- a/drivers/lguest/interrupts_and_traps.c +++ /dev/null @@ -1,706 +0,0 @@ -/*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 = IA32_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 push_guest_interrupt_stack() routine saves Guest state on the stack for - * an 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. - * - * 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 push_guest_interrupt_stack(struct lg_cpu *cpu, 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); - - /* Adjust the stack pointer and stack segment. */ - cpu->regs->ss = ss; - cpu->regs->esp = virtstack + (gstack - origstack); -} - -/* - * This actually makes the Guest start executing the given interrupt/trap - * handler. - * - * "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. - */ -static void guest_run_interrupt(struct lg_cpu *cpu, u32 lo, u32 hi) -{ - /* If we're already in the kernel, we don't change stacks. */ - if ((cpu->regs->ss&0x3) != GUEST_PL) - cpu->regs->ss = cpu->esp1; - - /* - * Set the code segment and the address to execute. - */ - cpu->regs->cs = (__KERNEL_CS|GUEST_PL); - cpu->regs->eip = idt_address(lo, hi); - - /* - * Trapping always clears these flags: - * TF: Trap flag - * VM: Virtual 8086 mode - * RF: Resume - * NT: Nested task. - */ - cpu->regs->eflags &= - ~(X86_EFLAGS_TF|X86_EFLAGS_VM|X86_EFLAGS_RF|X86_EFLAGS_NT); - - /* - * 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"); -} - -/* This restores the eflags word which was pushed on the stack by a trap */ -static void restore_eflags(struct lg_cpu *cpu) -{ - /* This is the physical address of the stack. */ - unsigned long stack_pa = guest_pa(cpu, cpu->regs->esp); - - /* - * Stack looks like this: - * Address Contents - * esp EIP - * esp + 4 CS - * esp + 8 EFLAGS - */ - cpu->regs->eflags = lgread(cpu, stack_pa + 8, u32); - cpu->regs->eflags &= - ~(X86_EFLAGS_TF|X86_EFLAGS_VM|X86_EFLAGS_RF|X86_EFLAGS_NT); -} - -/*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); - - /* 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); - - /* - * They may be about to iret, where they asked us never to - * deliver interrupts. In this case, we can emulate that iret - * then immediately deliver the interrupt. This is basically - * a noop: the iret would pop the interrupt frame and restore - * eflags, and then we'd set it up again. So just restore the - * eflags word and jump straight to the handler in this case. - * - * Denys Vlasenko points out that this isn't quite right: if - * the iret was returning to userspace, then that interrupt - * would reset the stack pointer (which the Guest told us - * about via LHCALL_SET_STACK). But unless the Guest is being - * *really* weird, that will be the same as the current stack - * anyway. - */ - if (cpu->regs->eip == cpu->lg->noirq_iret) { - restore_eflags(cpu); - } else { - /* - * set_guest_interrupt() takes a flag to say whether - * this interrupt pushes an error code onto the stack - * as well: virtual interrupts never do. - */ - push_guest_interrupt_stack(cpu, false); - } - /* Actually make Guest cpu jump to handler. */ - guest_run_interrupt(cpu, idt->a, idt->b); - } - - /* - * 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. - */ -bool could_be_syscall(unsigned int num) -{ - /* Normal Linux IA32_SYSCALL_VECTOR or reserved vector? */ - return num == IA32_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 != IA32_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\n", - syscall_vector); - return -EBUSY; - } - set_bit(syscall_vector, used_vectors); - } - - return 0; -} - -void free_interrupts(void) -{ - if (syscall_vector != IA32_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; - push_guest_interrupt_stack(cpu, has_err(num)); - guest_run_interrupt(cpu, cpu->arch.idt[num].a, - cpu->arch.idt[num].b); - 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. - * - * Unfortunately, Linux 4.6 started using an interrupt gate instead of a - * trap gate for syscalls, so this trick is ineffective. See Mastery for - * how we could do this anyway... - */ -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. The Host could provide a mechanism to register more - * "no-interrupt" regions, and the Guest could point the trap gate at - * instructions within that region, 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; -} |