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a32a8813d0
lguest never checked for pending interrupts when enabling interrupts, and things still worked. However, it makes a significant difference to TCP performance, so it's time we fixed it by introducing a pending_irq flag and checking it on irq_restore and irq_enable. These two routines are now too big to patch into the 8/10 bytes patch space, so we drop that code. Note: The high latency on interrupt delivery had a very curious effect: once everything else was optimized, networking without GSO was faster than networking with GSO, since more interrupts were sent and hence a greater chance of one getting through to the Guest! Note2: (Almost) Closing the same loophole for iret doesn't have any measurable effect, so I'm leaving that patch for the moment. Before: 1GB tcpblast Guest->Host: 30.7 seconds 1GB tcpblast Guest->Host (no GSO): 76.0 seconds After: 1GB tcpblast Guest->Host: 6.8 seconds 1GB tcpblast Guest->Host (no GSO): 27.8 seconds Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
544 lines
20 KiB
C
544 lines
20 KiB
C
/*P:800 Interrupts (traps) are complicated enough to earn their own file.
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* There are three classes of interrupts:
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*
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* 1) Real hardware interrupts which occur while we're running the Guest,
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* 2) Interrupts for virtual devices attached to the Guest, and
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* 3) Traps and faults from the Guest.
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*
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* Real hardware interrupts must be delivered to the Host, not the Guest.
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* Virtual interrupts must be delivered to the Guest, but we make them look
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* just like real hardware would deliver them. Traps from the Guest can be set
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* up to go directly back into the Guest, but sometimes the Host wants to see
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* them first, so we also have a way of "reflecting" them into the Guest as if
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* they had been delivered to it directly. :*/
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#include <linux/uaccess.h>
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#include <linux/interrupt.h>
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#include <linux/module.h>
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#include "lg.h"
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/* Allow Guests to use a non-128 (ie. non-Linux) syscall trap. */
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static unsigned int syscall_vector = SYSCALL_VECTOR;
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module_param(syscall_vector, uint, 0444);
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/* The address of the interrupt handler is split into two bits: */
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static unsigned long idt_address(u32 lo, u32 hi)
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{
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return (lo & 0x0000FFFF) | (hi & 0xFFFF0000);
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}
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/* The "type" of the interrupt handler is a 4 bit field: we only support a
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* couple of types. */
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static int idt_type(u32 lo, u32 hi)
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{
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return (hi >> 8) & 0xF;
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}
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/* An IDT entry can't be used unless the "present" bit is set. */
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static bool idt_present(u32 lo, u32 hi)
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{
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return (hi & 0x8000);
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}
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/* We need a helper to "push" a value onto the Guest's stack, since that's a
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* big part of what delivering an interrupt does. */
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static void push_guest_stack(struct lg_cpu *cpu, unsigned long *gstack, u32 val)
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{
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/* Stack grows upwards: move stack then write value. */
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*gstack -= 4;
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lgwrite(cpu, *gstack, u32, val);
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}
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/*H:210 The set_guest_interrupt() routine actually delivers the interrupt or
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* trap. The mechanics of delivering traps and interrupts to the Guest are the
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* same, except some traps have an "error code" which gets pushed onto the
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* stack as well: the caller tells us if this is one.
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*
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* "lo" and "hi" are the two parts of the Interrupt Descriptor Table for this
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* interrupt or trap. It's split into two parts for traditional reasons: gcc
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* on i386 used to be frightened by 64 bit numbers.
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*
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* We set up the stack just like the CPU does for a real interrupt, so it's
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* identical for the Guest (and the standard "iret" instruction will undo
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* it). */
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static void set_guest_interrupt(struct lg_cpu *cpu, u32 lo, u32 hi,
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bool has_err)
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{
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unsigned long gstack, origstack;
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u32 eflags, ss, irq_enable;
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unsigned long virtstack;
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/* There are two cases for interrupts: one where the Guest is already
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* in the kernel, and a more complex one where the Guest is in
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* userspace. We check the privilege level to find out. */
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if ((cpu->regs->ss&0x3) != GUEST_PL) {
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/* The Guest told us their kernel stack with the SET_STACK
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* hypercall: both the virtual address and the segment */
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virtstack = cpu->esp1;
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ss = cpu->ss1;
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origstack = gstack = guest_pa(cpu, virtstack);
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/* We push the old stack segment and pointer onto the new
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* stack: when the Guest does an "iret" back from the interrupt
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* handler the CPU will notice they're dropping privilege
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* levels and expect these here. */
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push_guest_stack(cpu, &gstack, cpu->regs->ss);
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push_guest_stack(cpu, &gstack, cpu->regs->esp);
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} else {
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/* We're staying on the same Guest (kernel) stack. */
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virtstack = cpu->regs->esp;
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ss = cpu->regs->ss;
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origstack = gstack = guest_pa(cpu, virtstack);
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}
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/* Remember that we never let the Guest actually disable interrupts, so
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* the "Interrupt Flag" bit is always set. We copy that bit from the
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* Guest's "irq_enabled" field into the eflags word: we saw the Guest
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* copy it back in "lguest_iret". */
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eflags = cpu->regs->eflags;
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if (get_user(irq_enable, &cpu->lg->lguest_data->irq_enabled) == 0
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&& !(irq_enable & X86_EFLAGS_IF))
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eflags &= ~X86_EFLAGS_IF;
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/* An interrupt is expected to push three things on the stack: the old
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* "eflags" word, the old code segment, and the old instruction
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* pointer. */
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push_guest_stack(cpu, &gstack, eflags);
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push_guest_stack(cpu, &gstack, cpu->regs->cs);
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push_guest_stack(cpu, &gstack, cpu->regs->eip);
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/* For the six traps which supply an error code, we push that, too. */
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if (has_err)
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push_guest_stack(cpu, &gstack, cpu->regs->errcode);
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/* Now we've pushed all the old state, we change the stack, the code
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* segment and the address to execute. */
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cpu->regs->ss = ss;
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cpu->regs->esp = virtstack + (gstack - origstack);
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cpu->regs->cs = (__KERNEL_CS|GUEST_PL);
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cpu->regs->eip = idt_address(lo, hi);
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/* There are two kinds of interrupt handlers: 0xE is an "interrupt
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* gate" which expects interrupts to be disabled on entry. */
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if (idt_type(lo, hi) == 0xE)
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if (put_user(0, &cpu->lg->lguest_data->irq_enabled))
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kill_guest(cpu, "Disabling interrupts");
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}
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/*H:205
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* Virtual Interrupts.
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*
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* interrupt_pending() returns the first pending interrupt which isn't blocked
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* by the Guest. It is called before every entry to the Guest, and just before
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* we go to sleep when the Guest has halted itself. */
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unsigned int interrupt_pending(struct lg_cpu *cpu, bool *more)
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{
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unsigned int irq;
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DECLARE_BITMAP(blk, LGUEST_IRQS);
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/* If the Guest hasn't even initialized yet, we can do nothing. */
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if (!cpu->lg->lguest_data)
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return LGUEST_IRQS;
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/* Take our "irqs_pending" array and remove any interrupts the Guest
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* wants blocked: the result ends up in "blk". */
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if (copy_from_user(&blk, cpu->lg->lguest_data->blocked_interrupts,
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sizeof(blk)))
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return LGUEST_IRQS;
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bitmap_andnot(blk, cpu->irqs_pending, blk, LGUEST_IRQS);
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/* Find the first interrupt. */
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irq = find_first_bit(blk, LGUEST_IRQS);
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*more = find_next_bit(blk, LGUEST_IRQS, irq+1);
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return irq;
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}
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/* This actually diverts the Guest to running an interrupt handler, once an
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* interrupt has been identified by interrupt_pending(). */
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void try_deliver_interrupt(struct lg_cpu *cpu, unsigned int irq, bool more)
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{
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struct desc_struct *idt;
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BUG_ON(irq >= LGUEST_IRQS);
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/* They may be in the middle of an iret, where they asked us never to
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* deliver interrupts. */
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if (cpu->regs->eip >= cpu->lg->noirq_start &&
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(cpu->regs->eip < cpu->lg->noirq_end))
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return;
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/* If they're halted, interrupts restart them. */
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if (cpu->halted) {
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/* Re-enable interrupts. */
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if (put_user(X86_EFLAGS_IF, &cpu->lg->lguest_data->irq_enabled))
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kill_guest(cpu, "Re-enabling interrupts");
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cpu->halted = 0;
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} else {
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/* Otherwise we check if they have interrupts disabled. */
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u32 irq_enabled;
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if (get_user(irq_enabled, &cpu->lg->lguest_data->irq_enabled))
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irq_enabled = 0;
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if (!irq_enabled) {
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/* Make sure they know an IRQ is pending. */
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put_user(X86_EFLAGS_IF,
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&cpu->lg->lguest_data->irq_pending);
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return;
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}
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}
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/* Look at the IDT entry the Guest gave us for this interrupt. The
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* first 32 (FIRST_EXTERNAL_VECTOR) entries are for traps, so we skip
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* over them. */
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idt = &cpu->arch.idt[FIRST_EXTERNAL_VECTOR+irq];
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/* If they don't have a handler (yet?), we just ignore it */
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if (idt_present(idt->a, idt->b)) {
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/* OK, mark it no longer pending and deliver it. */
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clear_bit(irq, cpu->irqs_pending);
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/* set_guest_interrupt() takes the interrupt descriptor and a
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* flag to say whether this interrupt pushes an error code onto
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* the stack as well: virtual interrupts never do. */
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set_guest_interrupt(cpu, idt->a, idt->b, false);
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}
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/* Every time we deliver an interrupt, we update the timestamp in the
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* Guest's lguest_data struct. It would be better for the Guest if we
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* did this more often, but it can actually be quite slow: doing it
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* here is a compromise which means at least it gets updated every
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* timer interrupt. */
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write_timestamp(cpu);
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/* If there are no other interrupts we want to deliver, clear
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* the pending flag. */
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if (!more)
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put_user(0, &cpu->lg->lguest_data->irq_pending);
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}
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/*:*/
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/* Linux uses trap 128 for system calls. Plan9 uses 64, and Ron Minnich sent
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* me a patch, so we support that too. It'd be a big step for lguest if half
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* the Plan 9 user base were to start using it.
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*
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* Actually now I think of it, it's possible that Ron *is* half the Plan 9
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* userbase. Oh well. */
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static bool could_be_syscall(unsigned int num)
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{
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/* Normal Linux SYSCALL_VECTOR or reserved vector? */
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return num == SYSCALL_VECTOR || num == syscall_vector;
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}
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/* The syscall vector it wants must be unused by Host. */
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bool check_syscall_vector(struct lguest *lg)
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{
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u32 vector;
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if (get_user(vector, &lg->lguest_data->syscall_vec))
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return false;
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return could_be_syscall(vector);
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}
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int init_interrupts(void)
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{
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/* If they want some strange system call vector, reserve it now */
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if (syscall_vector != SYSCALL_VECTOR) {
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if (test_bit(syscall_vector, used_vectors) ||
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vector_used_by_percpu_irq(syscall_vector)) {
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printk(KERN_ERR "lg: couldn't reserve syscall %u\n",
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syscall_vector);
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return -EBUSY;
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}
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set_bit(syscall_vector, used_vectors);
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}
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return 0;
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}
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void free_interrupts(void)
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{
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if (syscall_vector != SYSCALL_VECTOR)
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clear_bit(syscall_vector, used_vectors);
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}
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/*H:220 Now we've got the routines to deliver interrupts, delivering traps like
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* page fault is easy. The only trick is that Intel decided that some traps
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* should have error codes: */
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static bool has_err(unsigned int trap)
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{
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return (trap == 8 || (trap >= 10 && trap <= 14) || trap == 17);
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}
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/* deliver_trap() returns true if it could deliver the trap. */
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bool deliver_trap(struct lg_cpu *cpu, unsigned int num)
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{
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/* Trap numbers are always 8 bit, but we set an impossible trap number
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* for traps inside the Switcher, so check that here. */
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if (num >= ARRAY_SIZE(cpu->arch.idt))
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return false;
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/* Early on the Guest hasn't set the IDT entries (or maybe it put a
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* bogus one in): if we fail here, the Guest will be killed. */
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if (!idt_present(cpu->arch.idt[num].a, cpu->arch.idt[num].b))
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return false;
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set_guest_interrupt(cpu, cpu->arch.idt[num].a,
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cpu->arch.idt[num].b, has_err(num));
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return true;
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}
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/*H:250 Here's the hard part: returning to the Host every time a trap happens
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* and then calling deliver_trap() and re-entering the Guest is slow.
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* Particularly because Guest userspace system calls are traps (usually trap
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* 128).
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*
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* So we'd like to set up the IDT to tell the CPU to deliver traps directly
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* into the Guest. This is possible, but the complexities cause the size of
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* this file to double! However, 150 lines of code is worth writing for taking
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* system calls down from 1750ns to 270ns. Plus, if lguest didn't do it, all
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* the other hypervisors would beat it up at lunchtime.
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*
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* This routine indicates if a particular trap number could be delivered
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* directly. */
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static bool direct_trap(unsigned int num)
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{
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/* Hardware interrupts don't go to the Guest at all (except system
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* call). */
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if (num >= FIRST_EXTERNAL_VECTOR && !could_be_syscall(num))
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return false;
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/* The Host needs to see page faults (for shadow paging and to save the
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* fault address), general protection faults (in/out emulation) and
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* device not available (TS handling), invalid opcode fault (kvm hcall),
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* and of course, the hypercall trap. */
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return num != 14 && num != 13 && num != 7 &&
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num != 6 && num != LGUEST_TRAP_ENTRY;
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}
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/*:*/
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/*M:005 The Guest has the ability to turn its interrupt gates into trap gates,
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* if it is careful. The Host will let trap gates can go directly to the
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* Guest, but the Guest needs the interrupts atomically disabled for an
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* interrupt gate. It can do this by pointing the trap gate at instructions
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* within noirq_start and noirq_end, where it can safely disable interrupts. */
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/*M:006 The Guests do not use the sysenter (fast system call) instruction,
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* because it's hardcoded to enter privilege level 0 and so can't go direct.
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* It's about twice as fast as the older "int 0x80" system call, so it might
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* still be worthwhile to handle it in the Switcher and lcall down to the
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* Guest. The sysenter semantics are hairy tho: search for that keyword in
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* entry.S :*/
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/*H:260 When we make traps go directly into the Guest, we need to make sure
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* the kernel stack is valid (ie. mapped in the page tables). Otherwise, the
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* CPU trying to deliver the trap will fault while trying to push the interrupt
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* words on the stack: this is called a double fault, and it forces us to kill
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* the Guest.
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*
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* Which is deeply unfair, because (literally!) it wasn't the Guests' fault. */
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void pin_stack_pages(struct lg_cpu *cpu)
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{
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unsigned int i;
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/* Depending on the CONFIG_4KSTACKS option, the Guest can have one or
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* two pages of stack space. */
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for (i = 0; i < cpu->lg->stack_pages; i++)
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/* The stack grows *upwards*, so the address we're given is the
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* start of the page after the kernel stack. Subtract one to
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* get back onto the first stack page, and keep subtracting to
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* get to the rest of the stack pages. */
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pin_page(cpu, cpu->esp1 - 1 - i * PAGE_SIZE);
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}
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/* Direct traps also mean that we need to know whenever the Guest wants to use
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* a different kernel stack, so we can change the IDT entries to use that
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* stack. The IDT entries expect a virtual address, so unlike most addresses
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* the Guest gives us, the "esp" (stack pointer) value here is virtual, not
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* physical.
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*
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* In Linux each process has its own kernel stack, so this happens a lot: we
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* change stacks on each context switch. */
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void guest_set_stack(struct lg_cpu *cpu, u32 seg, u32 esp, unsigned int pages)
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{
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/* You are not allowed have a stack segment with privilege level 0: bad
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* Guest! */
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if ((seg & 0x3) != GUEST_PL)
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kill_guest(cpu, "bad stack segment %i", seg);
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/* We only expect one or two stack pages. */
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if (pages > 2)
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kill_guest(cpu, "bad stack pages %u", pages);
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/* Save where the stack is, and how many pages */
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cpu->ss1 = seg;
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cpu->esp1 = esp;
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cpu->lg->stack_pages = pages;
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/* Make sure the new stack pages are mapped */
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pin_stack_pages(cpu);
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}
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/* All this reference to mapping stacks leads us neatly into the other complex
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* part of the Host: page table handling. */
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/*H:235 This is the routine which actually checks the Guest's IDT entry and
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* transfers it into the entry in "struct lguest": */
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static void set_trap(struct lg_cpu *cpu, struct desc_struct *trap,
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unsigned int num, u32 lo, u32 hi)
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{
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u8 type = idt_type(lo, hi);
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/* We zero-out a not-present entry */
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if (!idt_present(lo, hi)) {
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trap->a = trap->b = 0;
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return;
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}
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/* We only support interrupt and trap gates. */
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if (type != 0xE && type != 0xF)
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kill_guest(cpu, "bad IDT type %i", type);
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/* We only copy the handler address, present bit, privilege level and
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* type. The privilege level controls where the trap can be triggered
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* manually with an "int" instruction. This is usually GUEST_PL,
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* except for system calls which userspace can use. */
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trap->a = ((__KERNEL_CS|GUEST_PL)<<16) | (lo&0x0000FFFF);
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trap->b = (hi&0xFFFFEF00);
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}
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/*H:230 While we're here, dealing with delivering traps and interrupts to the
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* Guest, we might as well complete the picture: how the Guest tells us where
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* it wants them to go. This would be simple, except making traps fast
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* requires some tricks.
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*
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* We saw the Guest setting Interrupt Descriptor Table (IDT) entries with the
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* LHCALL_LOAD_IDT_ENTRY hypercall before: that comes here. */
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void load_guest_idt_entry(struct lg_cpu *cpu, unsigned int num, u32 lo, u32 hi)
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{
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/* Guest never handles: NMI, doublefault, spurious interrupt or
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* hypercall. We ignore when it tries to set them. */
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if (num == 2 || num == 8 || num == 15 || num == LGUEST_TRAP_ENTRY)
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return;
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/* Mark the IDT as changed: next time the Guest runs we'll know we have
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* to copy this again. */
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cpu->changed |= CHANGED_IDT;
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/* Check that the Guest doesn't try to step outside the bounds. */
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if (num >= ARRAY_SIZE(cpu->arch.idt))
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kill_guest(cpu, "Setting idt entry %u", num);
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else
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set_trap(cpu, &cpu->arch.idt[num], num, lo, hi);
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}
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/* The default entry for each interrupt points into the Switcher routines which
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* simply return to the Host. The run_guest() loop will then call
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* deliver_trap() to bounce it back into the Guest. */
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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 priv. 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_bit(0, cpu->irqs_pending);
|
|
/* Guest may be stopped or running on another CPU. */
|
|
if (!wake_up_process(cpu->tsk))
|
|
kick_process(cpu->tsk);
|
|
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;
|
|
}
|