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f938d2c8 RR |
1 | /*P:800 Interrupts (traps) are complicated enough to earn their own file. |
2 | * There are three classes of interrupts: | |
3 | * | |
4 | * 1) Real hardware interrupts which occur while we're running the Guest, | |
5 | * 2) Interrupts for virtual devices attached to the Guest, and | |
6 | * 3) Traps and faults from the Guest. | |
7 | * | |
8 | * Real hardware interrupts must be delivered to the Host, not the Guest. | |
9 | * Virtual interrupts must be delivered to the Guest, but we make them look | |
10 | * just like real hardware would deliver them. Traps from the Guest can be set | |
11 | * up to go directly back into the Guest, but sometimes the Host wants to see | |
12 | * them first, so we also have a way of "reflecting" them into the Guest as if | |
13 | * they had been delivered to it directly. :*/ | |
d7e28ffe RR |
14 | #include <linux/uaccess.h> |
15 | #include "lg.h" | |
16 | ||
bff672e6 | 17 | /* The address of the interrupt handler is split into two bits: */ |
d7e28ffe RR |
18 | static unsigned long idt_address(u32 lo, u32 hi) |
19 | { | |
20 | return (lo & 0x0000FFFF) | (hi & 0xFFFF0000); | |
21 | } | |
22 | ||
bff672e6 RR |
23 | /* The "type" of the interrupt handler is a 4 bit field: we only support a |
24 | * couple of types. */ | |
d7e28ffe RR |
25 | static int idt_type(u32 lo, u32 hi) |
26 | { | |
27 | return (hi >> 8) & 0xF; | |
28 | } | |
29 | ||
bff672e6 | 30 | /* An IDT entry can't be used unless the "present" bit is set. */ |
d7e28ffe RR |
31 | static int idt_present(u32 lo, u32 hi) |
32 | { | |
33 | return (hi & 0x8000); | |
34 | } | |
35 | ||
bff672e6 RR |
36 | /* We need a helper to "push" a value onto the Guest's stack, since that's a |
37 | * big part of what delivering an interrupt does. */ | |
d7e28ffe RR |
38 | static void push_guest_stack(struct lguest *lg, unsigned long *gstack, u32 val) |
39 | { | |
bff672e6 | 40 | /* Stack grows upwards: move stack then write value. */ |
d7e28ffe RR |
41 | *gstack -= 4; |
42 | lgwrite_u32(lg, *gstack, val); | |
43 | } | |
44 | ||
bff672e6 RR |
45 | /*H:210 The set_guest_interrupt() routine actually delivers the interrupt or |
46 | * trap. The mechanics of delivering traps and interrupts to the Guest are the | |
47 | * same, except some traps have an "error code" which gets pushed onto the | |
48 | * stack as well: the caller tells us if this is one. | |
49 | * | |
50 | * "lo" and "hi" are the two parts of the Interrupt Descriptor Table for this | |
51 | * interrupt or trap. It's split into two parts for traditional reasons: gcc | |
52 | * on i386 used to be frightened by 64 bit numbers. | |
53 | * | |
54 | * We set up the stack just like the CPU does for a real interrupt, so it's | |
55 | * identical for the Guest (and the standard "iret" instruction will undo | |
56 | * it). */ | |
d7e28ffe RR |
57 | static void set_guest_interrupt(struct lguest *lg, u32 lo, u32 hi, int has_err) |
58 | { | |
59 | unsigned long gstack; | |
60 | u32 eflags, ss, irq_enable; | |
61 | ||
bff672e6 RR |
62 | /* There are two cases for interrupts: one where the Guest is already |
63 | * in the kernel, and a more complex one where the Guest is in | |
64 | * userspace. We check the privilege level to find out. */ | |
d7e28ffe | 65 | if ((lg->regs->ss&0x3) != GUEST_PL) { |
bff672e6 RR |
66 | /* The Guest told us their kernel stack with the SET_STACK |
67 | * hypercall: both the virtual address and the segment */ | |
d7e28ffe RR |
68 | gstack = guest_pa(lg, lg->esp1); |
69 | ss = lg->ss1; | |
bff672e6 RR |
70 | /* We push the old stack segment and pointer onto the new |
71 | * stack: when the Guest does an "iret" back from the interrupt | |
72 | * handler the CPU will notice they're dropping privilege | |
73 | * levels and expect these here. */ | |
d7e28ffe RR |
74 | push_guest_stack(lg, &gstack, lg->regs->ss); |
75 | push_guest_stack(lg, &gstack, lg->regs->esp); | |
76 | } else { | |
bff672e6 | 77 | /* We're staying on the same Guest (kernel) stack. */ |
d7e28ffe RR |
78 | gstack = guest_pa(lg, lg->regs->esp); |
79 | ss = lg->regs->ss; | |
80 | } | |
81 | ||
bff672e6 RR |
82 | /* Remember that we never let the Guest actually disable interrupts, so |
83 | * the "Interrupt Flag" bit is always set. We copy that bit from the | |
84 | * Guest's "irq_enabled" field into the eflags word: the Guest copies | |
85 | * it back in "lguest_iret". */ | |
d7e28ffe | 86 | eflags = lg->regs->eflags; |
e5faff45 RR |
87 | if (get_user(irq_enable, &lg->lguest_data->irq_enabled) == 0 |
88 | && !(irq_enable & X86_EFLAGS_IF)) | |
89 | eflags &= ~X86_EFLAGS_IF; | |
d7e28ffe | 90 | |
bff672e6 RR |
91 | /* An interrupt is expected to push three things on the stack: the old |
92 | * "eflags" word, the old code segment, and the old instruction | |
93 | * pointer. */ | |
d7e28ffe RR |
94 | push_guest_stack(lg, &gstack, eflags); |
95 | push_guest_stack(lg, &gstack, lg->regs->cs); | |
96 | push_guest_stack(lg, &gstack, lg->regs->eip); | |
97 | ||
bff672e6 | 98 | /* For the six traps which supply an error code, we push that, too. */ |
d7e28ffe RR |
99 | if (has_err) |
100 | push_guest_stack(lg, &gstack, lg->regs->errcode); | |
101 | ||
bff672e6 RR |
102 | /* Now we've pushed all the old state, we change the stack, the code |
103 | * segment and the address to execute. */ | |
d7e28ffe RR |
104 | lg->regs->ss = ss; |
105 | lg->regs->esp = gstack + lg->page_offset; | |
106 | lg->regs->cs = (__KERNEL_CS|GUEST_PL); | |
107 | lg->regs->eip = idt_address(lo, hi); | |
108 | ||
bff672e6 RR |
109 | /* There are two kinds of interrupt handlers: 0xE is an "interrupt |
110 | * gate" which expects interrupts to be disabled on entry. */ | |
d7e28ffe RR |
111 | if (idt_type(lo, hi) == 0xE) |
112 | if (put_user(0, &lg->lguest_data->irq_enabled)) | |
113 | kill_guest(lg, "Disabling interrupts"); | |
114 | } | |
115 | ||
bff672e6 RR |
116 | /*H:200 |
117 | * Virtual Interrupts. | |
118 | * | |
119 | * maybe_do_interrupt() gets called before every entry to the Guest, to see if | |
120 | * we should divert the Guest to running an interrupt handler. */ | |
d7e28ffe RR |
121 | void maybe_do_interrupt(struct lguest *lg) |
122 | { | |
123 | unsigned int irq; | |
124 | DECLARE_BITMAP(blk, LGUEST_IRQS); | |
125 | struct desc_struct *idt; | |
126 | ||
bff672e6 | 127 | /* If the Guest hasn't even initialized yet, we can do nothing. */ |
d7e28ffe RR |
128 | if (!lg->lguest_data) |
129 | return; | |
130 | ||
bff672e6 RR |
131 | /* Take our "irqs_pending" array and remove any interrupts the Guest |
132 | * wants blocked: the result ends up in "blk". */ | |
d7e28ffe RR |
133 | if (copy_from_user(&blk, lg->lguest_data->blocked_interrupts, |
134 | sizeof(blk))) | |
135 | return; | |
136 | ||
137 | bitmap_andnot(blk, lg->irqs_pending, blk, LGUEST_IRQS); | |
138 | ||
bff672e6 | 139 | /* Find the first interrupt. */ |
d7e28ffe | 140 | irq = find_first_bit(blk, LGUEST_IRQS); |
bff672e6 | 141 | /* None? Nothing to do */ |
d7e28ffe RR |
142 | if (irq >= LGUEST_IRQS) |
143 | return; | |
144 | ||
bff672e6 RR |
145 | /* They may be in the middle of an iret, where they asked us never to |
146 | * deliver interrupts. */ | |
d7e28ffe RR |
147 | if (lg->regs->eip >= lg->noirq_start && lg->regs->eip < lg->noirq_end) |
148 | return; | |
149 | ||
bff672e6 | 150 | /* If they're halted, interrupts restart them. */ |
d7e28ffe RR |
151 | if (lg->halted) { |
152 | /* Re-enable interrupts. */ | |
153 | if (put_user(X86_EFLAGS_IF, &lg->lguest_data->irq_enabled)) | |
154 | kill_guest(lg, "Re-enabling interrupts"); | |
155 | lg->halted = 0; | |
156 | } else { | |
bff672e6 | 157 | /* Otherwise we check if they have interrupts disabled. */ |
d7e28ffe RR |
158 | u32 irq_enabled; |
159 | if (get_user(irq_enabled, &lg->lguest_data->irq_enabled)) | |
160 | irq_enabled = 0; | |
161 | if (!irq_enabled) | |
162 | return; | |
163 | } | |
164 | ||
bff672e6 RR |
165 | /* Look at the IDT entry the Guest gave us for this interrupt. The |
166 | * first 32 (FIRST_EXTERNAL_VECTOR) entries are for traps, so we skip | |
167 | * over them. */ | |
d7e28ffe | 168 | idt = &lg->idt[FIRST_EXTERNAL_VECTOR+irq]; |
bff672e6 | 169 | /* If they don't have a handler (yet?), we just ignore it */ |
d7e28ffe | 170 | if (idt_present(idt->a, idt->b)) { |
bff672e6 | 171 | /* OK, mark it no longer pending and deliver it. */ |
d7e28ffe | 172 | clear_bit(irq, lg->irqs_pending); |
bff672e6 RR |
173 | /* set_guest_interrupt() takes the interrupt descriptor and a |
174 | * flag to say whether this interrupt pushes an error code onto | |
175 | * the stack as well: virtual interrupts never do. */ | |
d7e28ffe RR |
176 | set_guest_interrupt(lg, idt->a, idt->b, 0); |
177 | } | |
178 | } | |
179 | ||
bff672e6 RR |
180 | /*H:220 Now we've got the routines to deliver interrupts, delivering traps |
181 | * like page fault is easy. The only trick is that Intel decided that some | |
182 | * traps should have error codes: */ | |
d7e28ffe RR |
183 | static int has_err(unsigned int trap) |
184 | { | |
185 | return (trap == 8 || (trap >= 10 && trap <= 14) || trap == 17); | |
186 | } | |
187 | ||
bff672e6 | 188 | /* deliver_trap() returns true if it could deliver the trap. */ |
d7e28ffe RR |
189 | int deliver_trap(struct lguest *lg, unsigned int num) |
190 | { | |
191 | u32 lo = lg->idt[num].a, hi = lg->idt[num].b; | |
192 | ||
bff672e6 RR |
193 | /* Early on the Guest hasn't set the IDT entries (or maybe it put a |
194 | * bogus one in): if we fail here, the Guest will be killed. */ | |
d7e28ffe RR |
195 | if (!idt_present(lo, hi)) |
196 | return 0; | |
197 | set_guest_interrupt(lg, lo, hi, has_err(num)); | |
198 | return 1; | |
199 | } | |
200 | ||
bff672e6 RR |
201 | /*H:250 Here's the hard part: returning to the Host every time a trap happens |
202 | * and then calling deliver_trap() and re-entering the Guest is slow. | |
203 | * Particularly because Guest userspace system calls are traps (trap 128). | |
204 | * | |
205 | * So we'd like to set up the IDT to tell the CPU to deliver traps directly | |
206 | * into the Guest. This is possible, but the complexities cause the size of | |
207 | * this file to double! However, 150 lines of code is worth writing for taking | |
208 | * system calls down from 1750ns to 270ns. Plus, if lguest didn't do it, all | |
209 | * the other hypervisors would tease it. | |
210 | * | |
211 | * This routine determines if a trap can be delivered directly. */ | |
d7e28ffe RR |
212 | static int direct_trap(const struct lguest *lg, |
213 | const struct desc_struct *trap, | |
214 | unsigned int num) | |
215 | { | |
bff672e6 RR |
216 | /* Hardware interrupts don't go to the Guest at all (except system |
217 | * call). */ | |
d7e28ffe RR |
218 | if (num >= FIRST_EXTERNAL_VECTOR && num != SYSCALL_VECTOR) |
219 | return 0; | |
220 | ||
bff672e6 RR |
221 | /* The Host needs to see page faults (for shadow paging and to save the |
222 | * fault address), general protection faults (in/out emulation) and | |
223 | * device not available (TS handling), and of course, the hypercall | |
224 | * trap. */ | |
d7e28ffe RR |
225 | if (num == 14 || num == 13 || num == 7 || num == LGUEST_TRAP_ENTRY) |
226 | return 0; | |
227 | ||
bff672e6 RR |
228 | /* Only trap gates (type 15) can go direct to the Guest. Interrupt |
229 | * gates (type 14) disable interrupts as they are entered, which we | |
230 | * never let the Guest do. Not present entries (type 0x0) also can't | |
231 | * go direct, of course 8) */ | |
d7e28ffe RR |
232 | return idt_type(trap->a, trap->b) == 0xF; |
233 | } | |
f56a384e RR |
234 | /*:*/ |
235 | ||
236 | /*M:005 The Guest has the ability to turn its interrupt gates into trap gates, | |
237 | * if it is careful. The Host will let trap gates can go directly to the | |
238 | * Guest, but the Guest needs the interrupts atomically disabled for an | |
239 | * interrupt gate. It can do this by pointing the trap gate at instructions | |
240 | * within noirq_start and noirq_end, where it can safely disable interrupts. */ | |
241 | ||
242 | /*M:006 The Guests do not use the sysenter (fast system call) instruction, | |
243 | * because it's hardcoded to enter privilege level 0 and so can't go direct. | |
244 | * It's about twice as fast as the older "int 0x80" system call, so it might | |
245 | * still be worthwhile to handle it in the Switcher and lcall down to the | |
246 | * Guest. The sysenter semantics are hairy tho: search for that keyword in | |
247 | * entry.S :*/ | |
d7e28ffe | 248 | |
bff672e6 RR |
249 | /*H:260 When we make traps go directly into the Guest, we need to make sure |
250 | * the kernel stack is valid (ie. mapped in the page tables). Otherwise, the | |
251 | * CPU trying to deliver the trap will fault while trying to push the interrupt | |
252 | * words on the stack: this is called a double fault, and it forces us to kill | |
253 | * the Guest. | |
254 | * | |
255 | * Which is deeply unfair, because (literally!) it wasn't the Guests' fault. */ | |
d7e28ffe RR |
256 | void pin_stack_pages(struct lguest *lg) |
257 | { | |
258 | unsigned int i; | |
259 | ||
bff672e6 RR |
260 | /* Depending on the CONFIG_4KSTACKS option, the Guest can have one or |
261 | * two pages of stack space. */ | |
d7e28ffe | 262 | for (i = 0; i < lg->stack_pages; i++) |
bff672e6 | 263 | /* The stack grows *upwards*, hence the subtraction */ |
d7e28ffe RR |
264 | pin_page(lg, lg->esp1 - i * PAGE_SIZE); |
265 | } | |
266 | ||
bff672e6 RR |
267 | /* Direct traps also mean that we need to know whenever the Guest wants to use |
268 | * a different kernel stack, so we can change the IDT entries to use that | |
269 | * stack. The IDT entries expect a virtual address, so unlike most addresses | |
270 | * the Guest gives us, the "esp" (stack pointer) value here is virtual, not | |
271 | * physical. | |
272 | * | |
273 | * In Linux each process has its own kernel stack, so this happens a lot: we | |
274 | * change stacks on each context switch. */ | |
d7e28ffe RR |
275 | void guest_set_stack(struct lguest *lg, u32 seg, u32 esp, unsigned int pages) |
276 | { | |
bff672e6 RR |
277 | /* You are not allowd have a stack segment with privilege level 0: bad |
278 | * Guest! */ | |
d7e28ffe RR |
279 | if ((seg & 0x3) != GUEST_PL) |
280 | kill_guest(lg, "bad stack segment %i", seg); | |
bff672e6 | 281 | /* We only expect one or two stack pages. */ |
d7e28ffe RR |
282 | if (pages > 2) |
283 | kill_guest(lg, "bad stack pages %u", pages); | |
bff672e6 | 284 | /* Save where the stack is, and how many pages */ |
d7e28ffe RR |
285 | lg->ss1 = seg; |
286 | lg->esp1 = esp; | |
287 | lg->stack_pages = pages; | |
bff672e6 | 288 | /* Make sure the new stack pages are mapped */ |
d7e28ffe RR |
289 | pin_stack_pages(lg); |
290 | } | |
291 | ||
bff672e6 RR |
292 | /* All this reference to mapping stacks leads us neatly into the other complex |
293 | * part of the Host: page table handling. */ | |
294 | ||
295 | /*H:235 This is the routine which actually checks the Guest's IDT entry and | |
296 | * transfers it into our entry in "struct lguest": */ | |
d7e28ffe RR |
297 | static void set_trap(struct lguest *lg, struct desc_struct *trap, |
298 | unsigned int num, u32 lo, u32 hi) | |
299 | { | |
300 | u8 type = idt_type(lo, hi); | |
301 | ||
bff672e6 | 302 | /* We zero-out a not-present entry */ |
d7e28ffe RR |
303 | if (!idt_present(lo, hi)) { |
304 | trap->a = trap->b = 0; | |
305 | return; | |
306 | } | |
307 | ||
bff672e6 | 308 | /* We only support interrupt and trap gates. */ |
d7e28ffe RR |
309 | if (type != 0xE && type != 0xF) |
310 | kill_guest(lg, "bad IDT type %i", type); | |
311 | ||
bff672e6 RR |
312 | /* We only copy the handler address, present bit, privilege level and |
313 | * type. The privilege level controls where the trap can be triggered | |
314 | * manually with an "int" instruction. This is usually GUEST_PL, | |
315 | * except for system calls which userspace can use. */ | |
d7e28ffe RR |
316 | trap->a = ((__KERNEL_CS|GUEST_PL)<<16) | (lo&0x0000FFFF); |
317 | trap->b = (hi&0xFFFFEF00); | |
318 | } | |
319 | ||
bff672e6 RR |
320 | /*H:230 While we're here, dealing with delivering traps and interrupts to the |
321 | * Guest, we might as well complete the picture: how the Guest tells us where | |
322 | * it wants them to go. This would be simple, except making traps fast | |
323 | * requires some tricks. | |
324 | * | |
325 | * We saw the Guest setting Interrupt Descriptor Table (IDT) entries with the | |
326 | * LHCALL_LOAD_IDT_ENTRY hypercall before: that comes here. */ | |
d7e28ffe RR |
327 | void load_guest_idt_entry(struct lguest *lg, unsigned int num, u32 lo, u32 hi) |
328 | { | |
bff672e6 RR |
329 | /* Guest never handles: NMI, doublefault, spurious interrupt or |
330 | * hypercall. We ignore when it tries to set them. */ | |
d7e28ffe RR |
331 | if (num == 2 || num == 8 || num == 15 || num == LGUEST_TRAP_ENTRY) |
332 | return; | |
333 | ||
bff672e6 RR |
334 | /* Mark the IDT as changed: next time the Guest runs we'll know we have |
335 | * to copy this again. */ | |
d7e28ffe | 336 | lg->changed |= CHANGED_IDT; |
bff672e6 RR |
337 | |
338 | /* The IDT which we keep in "struct lguest" only contains 32 entries | |
339 | * for the traps and LGUEST_IRQS (32) entries for interrupts. We | |
340 | * ignore attempts to set handlers for higher interrupt numbers, except | |
341 | * for the system call "interrupt" at 128: we have a special IDT entry | |
342 | * for that. */ | |
d7e28ffe RR |
343 | if (num < ARRAY_SIZE(lg->idt)) |
344 | set_trap(lg, &lg->idt[num], num, lo, hi); | |
345 | else if (num == SYSCALL_VECTOR) | |
346 | set_trap(lg, &lg->syscall_idt, num, lo, hi); | |
347 | } | |
348 | ||
bff672e6 RR |
349 | /* The default entry for each interrupt points into the Switcher routines which |
350 | * simply return to the Host. The run_guest() loop will then call | |
351 | * deliver_trap() to bounce it back into the Guest. */ | |
d7e28ffe RR |
352 | static void default_idt_entry(struct desc_struct *idt, |
353 | int trap, | |
354 | const unsigned long handler) | |
355 | { | |
bff672e6 | 356 | /* A present interrupt gate. */ |
d7e28ffe RR |
357 | u32 flags = 0x8e00; |
358 | ||
bff672e6 RR |
359 | /* Set the privilege level on the entry for the hypercall: this allows |
360 | * the Guest to use the "int" instruction to trigger it. */ | |
d7e28ffe RR |
361 | if (trap == LGUEST_TRAP_ENTRY) |
362 | flags |= (GUEST_PL << 13); | |
363 | ||
bff672e6 | 364 | /* Now pack it into the IDT entry in its weird format. */ |
d7e28ffe RR |
365 | idt->a = (LGUEST_CS<<16) | (handler&0x0000FFFF); |
366 | idt->b = (handler&0xFFFF0000) | flags; | |
367 | } | |
368 | ||
bff672e6 | 369 | /* When the Guest first starts, we put default entries into the IDT. */ |
d7e28ffe RR |
370 | void setup_default_idt_entries(struct lguest_ro_state *state, |
371 | const unsigned long *def) | |
372 | { | |
373 | unsigned int i; | |
374 | ||
375 | for (i = 0; i < ARRAY_SIZE(state->guest_idt); i++) | |
376 | default_idt_entry(&state->guest_idt[i], i, def[i]); | |
377 | } | |
378 | ||
bff672e6 RR |
379 | /*H:240 We don't use the IDT entries in the "struct lguest" directly, instead |
380 | * we copy them into the IDT which we've set up for Guests on this CPU, just | |
381 | * before we run the Guest. This routine does that copy. */ | |
d7e28ffe RR |
382 | void copy_traps(const struct lguest *lg, struct desc_struct *idt, |
383 | const unsigned long *def) | |
384 | { | |
385 | unsigned int i; | |
386 | ||
bff672e6 RR |
387 | /* We can simply copy the direct traps, otherwise we use the default |
388 | * ones in the Switcher: they will return to the Host. */ | |
d7e28ffe RR |
389 | for (i = 0; i < FIRST_EXTERNAL_VECTOR; i++) { |
390 | if (direct_trap(lg, &lg->idt[i], i)) | |
391 | idt[i] = lg->idt[i]; | |
392 | else | |
393 | default_idt_entry(&idt[i], i, def[i]); | |
394 | } | |
bff672e6 RR |
395 | |
396 | /* Don't forget the system call trap! The IDT entries for other | |
397 | * interupts never change, so no need to copy them. */ | |
d7e28ffe RR |
398 | i = SYSCALL_VECTOR; |
399 | if (direct_trap(lg, &lg->syscall_idt, i)) | |
400 | idt[i] = lg->syscall_idt; | |
401 | else | |
402 | default_idt_entry(&idt[i], i, def[i]); | |
403 | } | |
404 | ||
405 | void guest_set_clockevent(struct lguest *lg, unsigned long delta) | |
406 | { | |
407 | ktime_t expires; | |
408 | ||
409 | if (unlikely(delta == 0)) { | |
410 | /* Clock event device is shutting down. */ | |
411 | hrtimer_cancel(&lg->hrt); | |
412 | return; | |
413 | } | |
414 | ||
415 | expires = ktime_add_ns(ktime_get_real(), delta); | |
416 | hrtimer_start(&lg->hrt, expires, HRTIMER_MODE_ABS); | |
417 | } | |
418 | ||
419 | static enum hrtimer_restart clockdev_fn(struct hrtimer *timer) | |
420 | { | |
421 | struct lguest *lg = container_of(timer, struct lguest, hrt); | |
422 | ||
423 | set_bit(0, lg->irqs_pending); | |
424 | if (lg->halted) | |
425 | wake_up_process(lg->tsk); | |
426 | return HRTIMER_NORESTART; | |
427 | } | |
428 | ||
429 | void init_clockdev(struct lguest *lg) | |
430 | { | |
431 | hrtimer_init(&lg->hrt, CLOCK_REALTIME, HRTIMER_MODE_ABS); | |
432 | lg->hrt.function = clockdev_fn; | |
433 | } |