2 * Copyright (C) 2006, Rusty Russell <rusty@rustcorp.com.au> IBM Corporation.
3 * Copyright (C) 2007, Jes Sorensen <jes@sgi.com> SGI.
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation; either version 2 of the License, or
8 * (at your option) any later version.
10 * This program is distributed in the hope that it will be useful, but
11 * WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
13 * NON INFRINGEMENT. See the GNU General Public License for more
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, write to the Free Software
18 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
20 #include <linux/kernel.h>
21 #include <linux/start_kernel.h>
22 #include <linux/string.h>
23 #include <linux/console.h>
24 #include <linux/screen_info.h>
25 #include <linux/irq.h>
26 #include <linux/interrupt.h>
27 #include <linux/clocksource.h>
28 #include <linux/clockchips.h>
29 #include <linux/cpu.h>
30 #include <linux/lguest.h>
31 #include <linux/lguest_launcher.h>
32 #include <asm/paravirt.h>
33 #include <asm/param.h>
35 #include <asm/pgtable.h>
37 #include <asm/setup.h>
38 #include <asm/lguest.h>
39 #include <asm/uaccess.h>
43 static int cpu_had_pge
;
47 unsigned short segment
;
50 /* Offset from where switcher.S was compiled to where we've copied it */
51 static unsigned long switcher_offset(void)
53 return SWITCHER_ADDR
- (unsigned long)start_switcher_text
;
56 /* This cpu's struct lguest_pages. */
57 static struct lguest_pages
*lguest_pages(unsigned int cpu
)
59 return &(((struct lguest_pages
*)
60 (SWITCHER_ADDR
+ SHARED_SWITCHER_PAGES
*PAGE_SIZE
))[cpu
]);
63 static DEFINE_PER_CPU(struct lg_cpu
*, last_cpu
);
66 * We approach the Switcher.
68 * Remember that each CPU has two pages which are visible to the Guest when it
69 * runs on that CPU. This has to contain the state for that Guest: we copy the
70 * state in just before we run the Guest.
72 * Each Guest has "changed" flags which indicate what has changed in the Guest
73 * since it last ran. We saw this set in interrupts_and_traps.c and
76 static void copy_in_guest_info(struct lg_cpu
*cpu
, struct lguest_pages
*pages
)
78 struct lguest
*lg
= cpu
->lg
;
79 /* Copying all this data can be quite expensive. We usually run the
80 * same Guest we ran last time (and that Guest hasn't run anywhere else
81 * meanwhile). If that's not the case, we pretend everything in the
82 * Guest has changed. */
83 if (__get_cpu_var(last_cpu
) != cpu
|| lg
->last_pages
!= pages
) {
84 __get_cpu_var(last_cpu
) = cpu
;
85 lg
->last_pages
= pages
;
86 lg
->changed
= CHANGED_ALL
;
89 /* These copies are pretty cheap, so we do them unconditionally: */
90 /* Save the current Host top-level page directory. */
91 pages
->state
.host_cr3
= __pa(current
->mm
->pgd
);
92 /* Set up the Guest's page tables to see this CPU's pages (and no
93 * other CPU's pages). */
94 map_switcher_in_guest(cpu
, pages
);
95 /* Set up the two "TSS" members which tell the CPU what stack to use
96 * for traps which do directly into the Guest (ie. traps at privilege
98 pages
->state
.guest_tss
.esp1
= cpu
->esp1
;
99 pages
->state
.guest_tss
.ss1
= cpu
->ss1
;
101 /* Copy direct-to-Guest trap entries. */
102 if (lg
->changed
& CHANGED_IDT
)
103 copy_traps(cpu
, pages
->state
.guest_idt
, default_idt_entries
);
105 /* Copy all GDT entries which the Guest can change. */
106 if (lg
->changed
& CHANGED_GDT
)
107 copy_gdt(cpu
, pages
->state
.guest_gdt
);
108 /* If only the TLS entries have changed, copy them. */
109 else if (lg
->changed
& CHANGED_GDT_TLS
)
110 copy_gdt_tls(cpu
, pages
->state
.guest_gdt
);
112 /* Mark the Guest as unchanged for next time. */
116 /* Finally: the code to actually call into the Switcher to run the Guest. */
117 static void run_guest_once(struct lg_cpu
*cpu
, struct lguest_pages
*pages
)
119 /* This is a dummy value we need for GCC's sake. */
120 unsigned int clobber
;
121 struct lguest
*lg
= cpu
->lg
;
123 /* Copy the guest-specific information into this CPU's "struct
125 copy_in_guest_info(cpu
, pages
);
127 /* Set the trap number to 256 (impossible value). If we fault while
128 * switching to the Guest (bad segment registers or bug), this will
129 * cause us to abort the Guest. */
130 cpu
->regs
->trapnum
= 256;
132 /* Now: we push the "eflags" register on the stack, then do an "lcall".
133 * This is how we change from using the kernel code segment to using
134 * the dedicated lguest code segment, as well as jumping into the
137 * The lcall also pushes the old code segment (KERNEL_CS) onto the
138 * stack, then the address of this call. This stack layout happens to
139 * exactly match the stack layout created by an interrupt... */
140 asm volatile("pushf; lcall *lguest_entry"
141 /* This is how we tell GCC that %eax ("a") and %ebx ("b")
142 * are changed by this routine. The "=" means output. */
143 : "=a"(clobber
), "=b"(clobber
)
144 /* %eax contains the pages pointer. ("0" refers to the
145 * 0-th argument above, ie "a"). %ebx contains the
146 * physical address of the Guest's top-level page
148 : "0"(pages
), "1"(__pa(lg
->pgdirs
[cpu
->cpu_pgd
].pgdir
))
149 /* We tell gcc that all these registers could change,
150 * which means we don't have to save and restore them in
152 : "memory", "%edx", "%ecx", "%edi", "%esi");
156 /*M:002 There are hooks in the scheduler which we can register to tell when we
157 * get kicked off the CPU (preempt_notifier_register()). This would allow us
158 * to lazily disable SYSENTER which would regain some performance, and should
159 * also simplify copy_in_guest_info(). Note that we'd still need to restore
160 * things when we exit to Launcher userspace, but that's fairly easy.
162 * The hooks were designed for KVM, but we can also put them to good use. :*/
164 /*H:040 This is the i386-specific code to setup and run the Guest. Interrupts
165 * are disabled: we own the CPU. */
166 void lguest_arch_run_guest(struct lg_cpu
*cpu
)
168 /* Remember the awfully-named TS bit? If the Guest has asked to set it
169 * we set it now, so we can trap and pass that trap to the Guest if it
174 /* SYSENTER is an optimized way of doing system calls. We can't allow
175 * it because it always jumps to privilege level 0. A normal Guest
176 * won't try it because we don't advertise it in CPUID, but a malicious
177 * Guest (or malicious Guest userspace program) could, so we tell the
178 * CPU to disable it before running the Guest. */
179 if (boot_cpu_has(X86_FEATURE_SEP
))
180 wrmsr(MSR_IA32_SYSENTER_CS
, 0, 0);
182 /* Now we actually run the Guest. It will return when something
183 * interesting happens, and we can examine its registers to see what it
185 run_guest_once(cpu
, lguest_pages(raw_smp_processor_id()));
187 /* Note that the "regs" pointer contains two extra entries which are
188 * not really registers: a trap number which says what interrupt or
189 * trap made the switcher code come back, and an error code which some
192 /* If the Guest page faulted, then the cr2 register will tell us the
193 * bad virtual address. We have to grab this now, because once we
194 * re-enable interrupts an interrupt could fault and thus overwrite
195 * cr2, or we could even move off to a different CPU. */
196 if (cpu
->regs
->trapnum
== 14)
197 cpu
->arch
.last_pagefault
= read_cr2();
198 /* Similarly, if we took a trap because the Guest used the FPU,
199 * we have to restore the FPU it expects to see. */
200 else if (cpu
->regs
->trapnum
== 7)
201 math_state_restore();
203 /* Restore SYSENTER if it's supposed to be on. */
204 if (boot_cpu_has(X86_FEATURE_SEP
))
205 wrmsr(MSR_IA32_SYSENTER_CS
, __KERNEL_CS
, 0);
208 /*H:130 Now we've examined the hypercall code; our Guest can make requests.
209 * Our Guest is usually so well behaved; it never tries to do things it isn't
210 * allowed to, and uses hypercalls instead. Unfortunately, Linux's paravirtual
211 * infrastructure isn't quite complete, because it doesn't contain replacements
212 * for the Intel I/O instructions. As a result, the Guest sometimes fumbles
213 * across one during the boot process as it probes for various things which are
214 * usually attached to a PC.
216 * When the Guest uses one of these instructions, we get a trap (General
217 * Protection Fault) and come here. We see if it's one of those troublesome
218 * instructions and skip over it. We return true if we did. */
219 static int emulate_insn(struct lg_cpu
*cpu
)
221 struct lguest
*lg
= cpu
->lg
;
223 unsigned int insnlen
= 0, in
= 0, shift
= 0;
224 /* The eip contains the *virtual* address of the Guest's instruction:
225 * guest_pa just subtracts the Guest's page_offset. */
226 unsigned long physaddr
= guest_pa(cpu
, cpu
->regs
->eip
);
228 /* This must be the Guest kernel trying to do something, not userspace!
229 * The bottom two bits of the CS segment register are the privilege
231 if ((cpu
->regs
->cs
& 3) != GUEST_PL
)
234 /* Decoding x86 instructions is icky. */
235 insn
= lgread(lg
, physaddr
, u8
);
237 /* 0x66 is an "operand prefix". It means it's using the upper 16 bits
238 of the eax register. */
241 /* The instruction is 1 byte so far, read the next byte. */
243 insn
= lgread(lg
, physaddr
+ insnlen
, u8
);
246 /* We can ignore the lower bit for the moment and decode the 4 opcodes
247 * we need to emulate. */
248 switch (insn
& 0xFE) {
249 case 0xE4: /* in <next byte>,%al */
253 case 0xEC: /* in (%dx),%al */
257 case 0xE6: /* out %al,<next byte> */
260 case 0xEE: /* out %al,(%dx) */
264 /* OK, we don't know what this is, can't emulate. */
268 /* If it was an "IN" instruction, they expect the result to be read
269 * into %eax, so we change %eax. We always return all-ones, which
270 * traditionally means "there's nothing there". */
272 /* Lower bit tells is whether it's a 16 or 32 bit access */
274 cpu
->regs
->eax
= 0xFFFFFFFF;
276 cpu
->regs
->eax
|= (0xFFFF << shift
);
278 /* Finally, we've "done" the instruction, so move past it. */
279 cpu
->regs
->eip
+= insnlen
;
284 /*H:050 Once we've re-enabled interrupts, we look at why the Guest exited. */
285 void lguest_arch_handle_trap(struct lg_cpu
*cpu
)
287 struct lguest
*lg
= cpu
->lg
;
288 switch (cpu
->regs
->trapnum
) {
289 case 13: /* We've intercepted a General Protection Fault. */
290 /* Check if this was one of those annoying IN or OUT
291 * instructions which we need to emulate. If so, we just go
292 * back into the Guest after we've done it. */
293 if (cpu
->regs
->errcode
== 0) {
294 if (emulate_insn(cpu
))
298 case 14: /* We've intercepted a Page Fault. */
299 /* The Guest accessed a virtual address that wasn't mapped.
300 * This happens a lot: we don't actually set up most of the
301 * page tables for the Guest at all when we start: as it runs
302 * it asks for more and more, and we set them up as
303 * required. In this case, we don't even tell the Guest that
304 * the fault happened.
306 * The errcode tells whether this was a read or a write, and
307 * whether kernel or userspace code. */
308 if (demand_page(cpu
, cpu
->arch
.last_pagefault
,
312 /* OK, it's really not there (or not OK): the Guest needs to
313 * know. We write out the cr2 value so it knows where the
316 * Note that if the Guest were really messed up, this could
317 * happen before it's done the LHCALL_LGUEST_INIT hypercall, so
318 * lg->lguest_data could be NULL */
319 if (lg
->lguest_data
&&
320 put_user(cpu
->arch
.last_pagefault
, &lg
->lguest_data
->cr2
))
321 kill_guest(lg
, "Writing cr2");
323 case 7: /* We've intercepted a Device Not Available fault. */
324 /* If the Guest doesn't want to know, we already restored the
325 * Floating Point Unit, so we just continue without telling
331 /* These values mean a real interrupt occurred, in which case
332 * the Host handler has already been run. We just do a
333 * friendly check if another process should now be run, then
334 * return to run the Guest again */
337 case LGUEST_TRAP_ENTRY
:
338 /* Our 'struct hcall_args' maps directly over our regs: we set
339 * up the pointer now to indicate a hypercall is pending. */
340 cpu
->hcall
= (struct hcall_args
*)cpu
->regs
;
344 /* We didn't handle the trap, so it needs to go to the Guest. */
345 if (!deliver_trap(cpu
, cpu
->regs
->trapnum
))
346 /* If the Guest doesn't have a handler (either it hasn't
347 * registered any yet, or it's one of the faults we don't let
348 * it handle), it dies with a cryptic error message. */
349 kill_guest(lg
, "unhandled trap %li at %#lx (%#lx)",
350 cpu
->regs
->trapnum
, cpu
->regs
->eip
,
351 cpu
->regs
->trapnum
== 14 ? cpu
->arch
.last_pagefault
352 : cpu
->regs
->errcode
);
355 /* Now we can look at each of the routines this calls, in increasing order of
356 * complexity: do_hypercalls(), emulate_insn(), maybe_do_interrupt(),
357 * deliver_trap() and demand_page(). After all those, we'll be ready to
358 * examine the Switcher, and our philosophical understanding of the Host/Guest
359 * duality will be complete. :*/
360 static void adjust_pge(void *on
)
363 write_cr4(read_cr4() | X86_CR4_PGE
);
365 write_cr4(read_cr4() & ~X86_CR4_PGE
);
368 /*H:020 Now the Switcher is mapped and every thing else is ready, we need to do
369 * some more i386-specific initialization. */
370 void __init
lguest_arch_host_init(void)
374 /* Most of the i386/switcher.S doesn't care that it's been moved; on
375 * Intel, jumps are relative, and it doesn't access any references to
376 * external code or data.
378 * The only exception is the interrupt handlers in switcher.S: their
379 * addresses are placed in a table (default_idt_entries), so we need to
380 * update the table with the new addresses. switcher_offset() is a
381 * convenience function which returns the distance between the builtin
382 * switcher code and the high-mapped copy we just made. */
383 for (i
= 0; i
< IDT_ENTRIES
; i
++)
384 default_idt_entries
[i
] += switcher_offset();
387 * Set up the Switcher's per-cpu areas.
389 * Each CPU gets two pages of its own within the high-mapped region
390 * (aka. "struct lguest_pages"). Much of this can be initialized now,
391 * but some depends on what Guest we are running (which is set up in
392 * copy_in_guest_info()).
394 for_each_possible_cpu(i
) {
395 /* lguest_pages() returns this CPU's two pages. */
396 struct lguest_pages
*pages
= lguest_pages(i
);
397 /* This is a convenience pointer to make the code fit one
398 * statement to a line. */
399 struct lguest_ro_state
*state
= &pages
->state
;
401 /* The Global Descriptor Table: the Host has a different one
402 * for each CPU. We keep a descriptor for the GDT which says
403 * where it is and how big it is (the size is actually the last
404 * byte, not the size, hence the "-1"). */
405 state
->host_gdt_desc
.size
= GDT_SIZE
-1;
406 state
->host_gdt_desc
.address
= (long)get_cpu_gdt_table(i
);
408 /* All CPUs on the Host use the same Interrupt Descriptor
409 * Table, so we just use store_idt(), which gets this CPU's IDT
411 store_idt(&state
->host_idt_desc
);
413 /* The descriptors for the Guest's GDT and IDT can be filled
414 * out now, too. We copy the GDT & IDT into ->guest_gdt and
415 * ->guest_idt before actually running the Guest. */
416 state
->guest_idt_desc
.size
= sizeof(state
->guest_idt
)-1;
417 state
->guest_idt_desc
.address
= (long)&state
->guest_idt
;
418 state
->guest_gdt_desc
.size
= sizeof(state
->guest_gdt
)-1;
419 state
->guest_gdt_desc
.address
= (long)&state
->guest_gdt
;
421 /* We know where we want the stack to be when the Guest enters
422 * the switcher: in pages->regs. The stack grows upwards, so
423 * we start it at the end of that structure. */
424 state
->guest_tss
.esp0
= (long)(&pages
->regs
+ 1);
425 /* And this is the GDT entry to use for the stack: we keep a
426 * couple of special LGUEST entries. */
427 state
->guest_tss
.ss0
= LGUEST_DS
;
429 /* x86 can have a finegrained bitmap which indicates what I/O
430 * ports the process can use. We set it to the end of our
431 * structure, meaning "none". */
432 state
->guest_tss
.io_bitmap_base
= sizeof(state
->guest_tss
);
434 /* Some GDT entries are the same across all Guests, so we can
435 * set them up now. */
436 setup_default_gdt_entries(state
);
437 /* Most IDT entries are the same for all Guests, too.*/
438 setup_default_idt_entries(state
, default_idt_entries
);
440 /* The Host needs to be able to use the LGUEST segments on this
441 * CPU, too, so put them in the Host GDT. */
442 get_cpu_gdt_table(i
)[GDT_ENTRY_LGUEST_CS
] = FULL_EXEC_SEGMENT
;
443 get_cpu_gdt_table(i
)[GDT_ENTRY_LGUEST_DS
] = FULL_SEGMENT
;
446 /* In the Switcher, we want the %cs segment register to use the
447 * LGUEST_CS GDT entry: we've put that in the Host and Guest GDTs, so
448 * it will be undisturbed when we switch. To change %cs and jump we
449 * need this structure to feed to Intel's "lcall" instruction. */
450 lguest_entry
.offset
= (long)switch_to_guest
+ switcher_offset();
451 lguest_entry
.segment
= LGUEST_CS
;
453 /* Finally, we need to turn off "Page Global Enable". PGE is an
454 * optimization where page table entries are specially marked to show
455 * they never change. The Host kernel marks all the kernel pages this
456 * way because it's always present, even when userspace is running.
458 * Lguest breaks this: unbeknownst to the rest of the Host kernel, we
459 * switch to the Guest kernel. If you don't disable this on all CPUs,
460 * you'll get really weird bugs that you'll chase for two days.
462 * I used to turn PGE off every time we switched to the Guest and back
463 * on when we return, but that slowed the Switcher down noticibly. */
465 /* We don't need the complexity of CPUs coming and going while we're
468 if (cpu_has_pge
) { /* We have a broader idea of "global". */
469 /* Remember that this was originally set (for cleanup). */
471 /* adjust_pge is a helper function which sets or unsets the PGE
472 * bit on its CPU, depending on the argument (0 == unset). */
473 on_each_cpu(adjust_pge
, (void *)0, 0, 1);
474 /* Turn off the feature in the global feature set. */
475 clear_bit(X86_FEATURE_PGE
, boot_cpu_data
.x86_capability
);
481 void __exit
lguest_arch_host_fini(void)
483 /* If we had PGE before we started, turn it back on now. */
486 set_bit(X86_FEATURE_PGE
, boot_cpu_data
.x86_capability
);
487 /* adjust_pge's argument "1" means set PGE. */
488 on_each_cpu(adjust_pge
, (void *)1, 0, 1);
494 /*H:122 The i386-specific hypercalls simply farm out to the right functions. */
495 int lguest_arch_do_hcall(struct lg_cpu
*cpu
, struct hcall_args
*args
)
497 switch (args
->arg0
) {
498 case LHCALL_LOAD_GDT
:
499 load_guest_gdt(cpu
, args
->arg1
, args
->arg2
);
501 case LHCALL_LOAD_IDT_ENTRY
:
502 load_guest_idt_entry(cpu
, args
->arg1
, args
->arg2
, args
->arg3
);
504 case LHCALL_LOAD_TLS
:
505 guest_load_tls(cpu
, args
->arg1
);
508 /* Bad Guest. Bad! */
514 /*H:126 i386-specific hypercall initialization: */
515 int lguest_arch_init_hypercalls(struct lg_cpu
*cpu
)
518 struct lguest
*lg
= cpu
->lg
;
520 /* The pointer to the Guest's "struct lguest_data" is the only
521 * argument. We check that address now. */
522 if (!lguest_address_ok(lg
, cpu
->hcall
->arg1
, sizeof(*lg
->lguest_data
)))
525 /* Having checked it, we simply set lg->lguest_data to point straight
526 * into the Launcher's memory at the right place and then use
527 * copy_to_user/from_user from now on, instead of lgread/write. I put
528 * this in to show that I'm not immune to writing stupid
530 lg
->lguest_data
= lg
->mem_base
+ cpu
->hcall
->arg1
;
532 /* We insist that the Time Stamp Counter exist and doesn't change with
533 * cpu frequency. Some devious chip manufacturers decided that TSC
534 * changes could be handled in software. I decided that time going
535 * backwards might be good for benchmarks, but it's bad for users.
537 * We also insist that the TSC be stable: the kernel detects unreliable
538 * TSCs for its own purposes, and we use that here. */
539 if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC
) && !check_tsc_unstable())
543 if (put_user(tsc_speed
, &lg
->lguest_data
->tsc_khz
))
546 /* The interrupt code might not like the system call vector. */
547 if (!check_syscall_vector(lg
))
548 kill_guest(lg
, "bad syscall vector");
553 /*L:030 lguest_arch_setup_regs()
555 * Most of the Guest's registers are left alone: we used get_zeroed_page() to
556 * allocate the structure, so they will be 0. */
557 void lguest_arch_setup_regs(struct lg_cpu
*cpu
, unsigned long start
)
559 struct lguest_regs
*regs
= cpu
->regs
;
561 /* There are four "segment" registers which the Guest needs to boot:
562 * The "code segment" register (cs) refers to the kernel code segment
563 * __KERNEL_CS, and the "data", "extra" and "stack" segment registers
564 * refer to the kernel data segment __KERNEL_DS.
566 * The privilege level is packed into the lower bits. The Guest runs
567 * at privilege level 1 (GUEST_PL).*/
568 regs
->ds
= regs
->es
= regs
->ss
= __KERNEL_DS
|GUEST_PL
;
569 regs
->cs
= __KERNEL_CS
|GUEST_PL
;
571 /* The "eflags" register contains miscellaneous flags. Bit 1 (0x002)
572 * is supposed to always be "1". Bit 9 (0x200) controls whether
573 * interrupts are enabled. We always leave interrupts enabled while
574 * running the Guest. */
575 regs
->eflags
= X86_EFLAGS_IF
| 0x2;
577 /* The "Extended Instruction Pointer" register says where the Guest is
581 /* %esi points to our boot information, at physical address 0, so don't
584 /* There are a couple of GDT entries the Guest expects when first
586 setup_guest_gdt(cpu
);
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