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lguest: fix comment style

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I don't really notice it (except to begrudge the extra vertical
space), but Ingo does.  And he pointed out that one excuse of lguest
is as a teaching tool, it should set a good example.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Ingo Molnar <mingo@redhat.com>
This commit is contained in:
Rusty Russell
2009-07-30 16:03:45 -06:00
parent e969fed542
commit 2e04ef7691
17 changed files with 1906 additions and 1015 deletions
Download Patch File Download Diff File Expand all files Collapse all files

288
drivers/lguest/interrupts_and_traps.c
View File

@@ -1,4 +1,5 @@
/*P:800 Interrupts (traps) are complicated enough to earn their own file.
/*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,
@@ -10,7 +11,8 @@
* 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. :*/
* they had been delivered to it directly.
:*/
#include <linux/uaccess.h>
#include <linux/interrupt.h>
#include <linux/module.h>
@@ -26,8 +28,10 @@ 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. */
/*
* 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;
@@ -39,8 +43,10 @@ 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. */
/*
* 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. */
@@ -48,7 +54,8 @@ static void push_guest_stack(struct lg_cpu *cpu, unsigned long *gstack, u32 val)
lgwrite(cpu, *gstack, u32, val);
}
/*H:210 The set_guest_interrupt() routine actually delivers the interrupt or
/*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.
@@ -59,7 +66,8 @@ static void push_guest_stack(struct lg_cpu *cpu, unsigned long *gstack, u32 val)
*
* 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). */
* it).
*/
static void set_guest_interrupt(struct lg_cpu *cpu, u32 lo, u32 hi,
bool has_err)
{
@@ -67,20 +75,26 @@ static void set_guest_interrupt(struct lg_cpu *cpu, u32 lo, u32 hi,
u32 eflags, ss, irq_enable;
unsigned long virtstack;
/* There are two cases for interrupts: one where the Guest is already
/*
* 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. */
* 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 */
/*
* 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
/*
* 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. */
* levels and expect these here.
*/
push_guest_stack(cpu, &gstack, cpu->regs->ss);
push_guest_stack(cpu, &gstack, cpu->regs->esp);
} else {
@@ -91,18 +105,22 @@ static void set_guest_interrupt(struct lg_cpu *cpu, u32 lo, u32 hi,
origstack = gstack = guest_pa(cpu, virtstack);
}
/* Remember that we never let the Guest actually disable interrupts, so
/*
* 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". */
* 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
/*
* An interrupt is expected to push three things on the stack: the old
* "eflags" word, the old code segment, and the old instruction
* pointer. */
* pointer.
*/
push_guest_stack(cpu, &gstack, eflags);
push_guest_stack(cpu, &gstack, cpu->regs->cs);
push_guest_stack(cpu, &gstack, cpu->regs->eip);
@@ -111,15 +129,19 @@ static void set_guest_interrupt(struct lg_cpu *cpu, u32 lo, u32 hi,
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. */
/*
* 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. */
/*
* 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");
@@ -130,7 +152,8 @@ static void set_guest_interrupt(struct lg_cpu *cpu, u32 lo, u32 hi,
*
* 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. */
* we go to sleep when the Guest has halted itself.
*/
unsigned int interrupt_pending(struct lg_cpu *cpu, bool *more)
{
unsigned int irq;
@@ -140,8 +163,10 @@ unsigned int interrupt_pending(struct lg_cpu *cpu, bool *more)
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". */
/*
* 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;
@@ -154,16 +179,20 @@ unsigned int interrupt_pending(struct lg_cpu *cpu, bool *more)
return irq;
}
/* This actually diverts the Guest to running an interrupt handler, once an
* interrupt has been identified by interrupt_pending(). */
/*
* 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. */
/*
* 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;
@@ -187,29 +216,37 @@ void try_deliver_interrupt(struct lg_cpu *cpu, unsigned int irq, bool more)
}
}
/* Look at the IDT entry the Guest gave us for this interrupt. The
/*
* 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. */
* 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
/*
* 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. */
* 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
/*
* 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. */
* timer interrupt.
*/
write_timestamp(cpu);
/* If there are no other interrupts we want to deliver, clear
* the pending flag. */
/*
* 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);
}
@@ -217,24 +254,29 @@ void try_deliver_interrupt(struct lg_cpu *cpu, unsigned int irq, bool more)
/* 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. */
/*
* 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. */
/*
* 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
/*
* 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. */
* userbase. Oh well.
*/
static bool could_be_syscall(unsigned int num)
{
/* Normal Linux SYSCALL_VECTOR or reserved vector? */
@@ -274,9 +316,11 @@ void free_interrupts(void)
clear_bit(syscall_vector, used_vectors);
}
/*H:220 Now we've got the routines to deliver interrupts, delivering traps like
/*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: */
* should have error codes:
*/
static bool has_err(unsigned int trap)
{
return (trap == 8 || (trap >= 10 && trap <= 14) || trap == 17);
@@ -285,13 +329,17 @@ static bool has_err(unsigned int trap)
/* 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. */
/*
* 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. */
/*
* 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,
@@ -299,7 +347,8 @@ bool deliver_trap(struct lg_cpu *cpu, unsigned int num)
return true;
}
/*H:250 Here's the hard part: returning to the Host every time a trap happens
/*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).
@@ -311,69 +360,87 @@ bool deliver_trap(struct lg_cpu *cpu, unsigned int num)
* the other hypervisors would beat it up at lunchtime.
*
* This routine indicates if a particular trap number could be delivered
* directly. */
* directly.
*/
static bool direct_trap(unsigned int num)
{
/* Hardware interrupts don't go to the Guest at all (except system
* call). */
/*
* 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
/*
* 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), invalid opcode fault (kvm hcall),
* and of course, the hypercall trap. */
* and of course, the hypercall trap.
*/
return num != 14 && num != 13 && num != 7 &&
num != 6 && num != LGUEST_TRAP_ENTRY;
}
/*:*/
/*M:005 The Guest has the ability to turn its interrupt gates into trap gates,
/*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. */
* 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,
/*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 :*/
* entry.S
:*/
/*H:260 When we make traps go directly into the Guest, we need to make sure
/*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. */
* 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. */
/*
* 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
/*
* 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. */
* 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
/*
* 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. */
* change stacks on each context switch.
*/
void guest_set_stack(struct lg_cpu *cpu, u32 seg, u32 esp, unsigned int pages)
{
/* You are not allowed have a stack segment with privilege level 0: bad
* Guest! */
/*
* 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. */
@@ -387,11 +454,15 @@ void guest_set_stack(struct lg_cpu *cpu, u32 seg, u32 esp, unsigned int pages)
pin_stack_pages(cpu);
}
/* All this reference to mapping stacks leads us neatly into the other complex
* part of the Host: page table handling. */
/*
* 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": */
/*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)
{
@@ -407,30 +478,38 @@ static void set_trap(struct lg_cpu *cpu, struct desc_struct *trap,
if (type != 0xE && type != 0xF)
kill_guest(cpu, "bad IDT type %i", type);
/* We only copy the handler address, present bit, privilege level and
/*
* 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. */
* 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
/*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. */
* 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. */
/*
* 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. */
/*
* 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. */
@@ -440,9 +519,11 @@ void load_guest_idt_entry(struct lg_cpu *cpu, unsigned int num, u32 lo, u32 hi)
set_trap(cpu, &cpu->arch.idt[num], num, lo, hi);
}
/* The default entry for each interrupt points into the Switcher routines which
/*
* 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. */
* deliver_trap() to bounce it back into the Guest.
*/
static void default_idt_entry(struct desc_struct *idt,
int trap,
const unsigned long handler,
@@ -451,13 +532,17 @@ static void default_idt_entry(struct desc_struct *idt,
/* 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. */
/*
* 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. */
/*
* 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. */
@@ -475,16 +560,20 @@ void setup_default_idt_entries(struct lguest_ro_state *state,
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
/*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. */
* 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. */
/*
* 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];
@@ -492,14 +581,16 @@ void copy_traps(const struct lg_cpu *cpu, struct desc_struct *idt,
if (!direct_trap(i))
continue;
/* Only trap gates (type 15) can go direct to the Guest.
/*
* 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. */
* interrupt.
*/
if (idt_type(gidt->a, gidt->b) == 0xF)
idt[i] = *gidt;
else
@@ -518,7 +609,8 @@ void copy_traps(const struct lg_cpu *cpu, struct desc_struct *idt,
* 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". */
* 0 means "turn off the clock".
*/
void guest_set_clockevent(struct lg_cpu *cpu, unsigned long delta)
{
ktime_t expires;
@@ -529,9 +621,11 @@ void guest_set_clockevent(struct lg_cpu *cpu, unsigned long delta)
return;
}
/* We use wallclock time here, so the Guest might not be running for
/*
* 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. */
* is almost always the right thing to do.
*/
expires = ktime_add_ns(ktime_get_real(), delta);
hrtimer_start(&cpu->hrt, expires, HRTIMER_MODE_ABS);
}