1 /*P:400 This contains run_guest() which actually calls into the Host<->Guest
2 * Switcher and analyzes the return, such as determining if the Guest wants the
3 * Host to do something. This file also contains useful helper routines. :*/
4 #include <linux/module.h>
5 #include <linux/stringify.h>
6 #include <linux/stddef.h>
7 #include <linux/io.h>
8 #include <linux/mm.h>
9 #include <linux/vmalloc.h>
10 #include <linux/cpu.h>
11 #include <linux/freezer.h>
12 #include <linux/highmem.h>
13 #include <asm/paravirt.h>
14 #include <asm/pgtable.h>
15 #include <asm/uaccess.h>
16 #include <asm/poll.h>
17 #include <asm/asm-offsets.h>
18 #include "lg.h"
19
20
21 static struct vm_struct *switcher_vma;
22 static struct page **switcher_page;
23
24 /* This One Big lock protects all inter-guest data structures. */
25 DEFINE_MUTEX(lguest_lock);
26
27 /*H:010 We need to set up the Switcher at a high virtual address. Remember the
28 * Switcher is a few hundred bytes of assembler code which actually changes the
29 * CPU to run the Guest, and then changes back to the Host when a trap or
30 * interrupt happens.
31 *
32 * The Switcher code must be at the same virtual address in the Guest as the
33 * Host since it will be running as the switchover occurs.
34 *
35 * Trying to map memory at a particular address is an unusual thing to do, so
36 * it's not a simple one-liner. */
37 static __init int map_switcher(void)
38 {
39 int i, err;
40 struct page **pagep;
41
42 /*
43 * Map the Switcher in to high memory.
44 *
45 * It turns out that if we choose the address 0xFFC00000 (4MB under the
46 * top virtual address), it makes setting up the page tables really
47 * easy.
48 */
49
50 /* We allocate an array of struct page pointers. map_vm_area() wants
51 * this, rather than just an array of pages. */
52 switcher_page = kmalloc(sizeof(switcher_page[0])*TOTAL_SWITCHER_PAGES,
53 GFP_KERNEL);
54 if (!switcher_page) {
55 err = -ENOMEM;
56 goto out;
57 }
58
59 /* Now we actually allocate the pages. The Guest will see these pages,
60 * so we make sure they're zeroed. */
61 for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) {
62 unsigned long addr = get_zeroed_page(GFP_KERNEL);
63 if (!addr) {
64 err = -ENOMEM;
65 goto free_some_pages;
66 }
67 switcher_page[i] = virt_to_page(addr);
68 }
69
70 /* First we check that the Switcher won't overlap the fixmap area at
71 * the top of memory. It's currently nowhere near, but it could have
72 * very strange effects if it ever happened. */
73 if (SWITCHER_ADDR + (TOTAL_SWITCHER_PAGES+1)*PAGE_SIZE > FIXADDR_START){
74 err = -ENOMEM;
75 printk("lguest: mapping switcher would thwack fixmap\n");
76 goto free_pages;
77 }
78
79 /* Now we reserve the "virtual memory area" we want: 0xFFC00000
80 * (SWITCHER_ADDR). We might not get it in theory, but in practice
81 * it's worked so far. The end address needs +1 because __get_vm_area
82 * allocates an extra guard page, so we need space for that. */
83 switcher_vma = __get_vm_area(TOTAL_SWITCHER_PAGES * PAGE_SIZE,
84 VM_ALLOC, SWITCHER_ADDR, SWITCHER_ADDR
85 + (TOTAL_SWITCHER_PAGES+1) * PAGE_SIZE);
86 if (!switcher_vma) {
87 err = -ENOMEM;
88 printk("lguest: could not map switcher pages high\n");
89 goto free_pages;
90 }
91
92 /* This code actually sets up the pages we've allocated to appear at
93 * SWITCHER_ADDR. map_vm_area() takes the vma we allocated above, the
94 * kind of pages we're mapping (kernel pages), and a pointer to our
95 * array of struct pages. It increments that pointer, but we don't
96 * care. */
97 pagep = switcher_page;
98 err = map_vm_area(switcher_vma, PAGE_KERNEL, &pagep);
99 if (err) {
100 printk("lguest: map_vm_area failed: %i\n", err);
101 goto free_vma;
102 }
103
104 /* Now the Switcher is mapped at the right address, we can't fail!
105 * Copy in the compiled-in Switcher code (from <arch>_switcher.S). */
106 memcpy(switcher_vma->addr, start_switcher_text,
107 end_switcher_text - start_switcher_text);
108
109 printk(KERN_INFO "lguest: mapped switcher at %p\n",
110 switcher_vma->addr);
111 /* And we succeeded... */
112 return 0;
113
114 free_vma:
115 vunmap(switcher_vma->addr);
116 free_pages:
117 i = TOTAL_SWITCHER_PAGES;
118 free_some_pages:
119 for (--i; i >= 0; i--)
120 __free_pages(switcher_page[i], 0);
121 kfree(switcher_page);
122 out:
123 return err;
124 }
125 /*:*/
126
127 /* Cleaning up the mapping when the module is unloaded is almost...
128 * too easy. */
129 static void unmap_switcher(void)
130 {
131 unsigned int i;
132
133 /* vunmap() undoes *both* map_vm_area() and __get_vm_area(). */
134 vunmap(switcher_vma->addr);
135 /* Now we just need to free the pages we copied the switcher into */
136 for (i = 0; i < TOTAL_SWITCHER_PAGES; i++)
137 __free_pages(switcher_page[i], 0);
138 }
139
140 /*H:032
141 * Dealing With Guest Memory.
142 *
143 * Before we go too much further into the Host, we need to grok the routines
144 * we use to deal with Guest memory.
145 *
146 * When the Guest gives us (what it thinks is) a physical address, we can use
147 * the normal copy_from_user() & copy_to_user() on the corresponding place in
148 * the memory region allocated by the Launcher.
149 *
150 * But we can't trust the Guest: it might be trying to access the Launcher
151 * code. We have to check that the range is below the pfn_limit the Launcher
152 * gave us. We have to make sure that addr + len doesn't give us a false
153 * positive by overflowing, too. */
154 int lguest_address_ok(const struct lguest *lg,
155 unsigned long addr, unsigned long len)
156 {
157 return (addr+len) / PAGE_SIZE < lg->pfn_limit && (addr+len >= addr);
158 }
159
160 /* This routine copies memory from the Guest. Here we can see how useful the
161 * kill_lguest() routine we met in the Launcher can be: we return a random
162 * value (all zeroes) instead of needing to return an error. */
163 void __lgread(struct lg_cpu *cpu, void *b, unsigned long addr, unsigned bytes)
164 {
165 if (!lguest_address_ok(cpu->lg, addr, bytes)
166 || copy_from_user(b, cpu->lg->mem_base + addr, bytes) != 0) {
167 /* copy_from_user should do this, but as we rely on it... */
168 memset(b, 0, bytes);
169 kill_guest(cpu, "bad read address %#lx len %u", addr, bytes);
170 }
171 }
172
173 /* This is the write (copy into Guest) version. */
174 void __lgwrite(struct lg_cpu *cpu, unsigned long addr, const void *b,
175 unsigned bytes)
176 {
177 if (!lguest_address_ok(cpu->lg, addr, bytes)
178 || copy_to_user(cpu->lg->mem_base + addr, b, bytes) != 0)
179 kill_guest(cpu, "bad write address %#lx len %u", addr, bytes);
180 }
181 /*:*/
182
183 /*H:030 Let's jump straight to the the main loop which runs the Guest.
184 * Remember, this is called by the Launcher reading /dev/lguest, and we keep
185 * going around and around until something interesting happens. */
186 int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
187 {
188 /* We stop running once the Guest is dead. */
189 while (!cpu->lg->dead) {
190 /* First we run any hypercalls the Guest wants done. */
191 if (cpu->hcall)
192 do_hypercalls(cpu);
193
194 /* It's possible the Guest did a NOTIFY hypercall to the
195 * Launcher, in which case we return from the read() now. */
196 if (cpu->pending_notify) {
197 if (put_user(cpu->pending_notify, user))
198 return -EFAULT;
199 return sizeof(cpu->pending_notify);
200 }
201
202 /* Check for signals */
203 if (signal_pending(current))
204 return -ERESTARTSYS;
205
206 /* If Waker set break_out, return to Launcher. */
207 if (cpu->break_out)
208 return -EAGAIN;
209
210 /* Check if there are any interrupts which can be delivered now:
211 * if so, this sets up the hander to be executed when we next
212 * run the Guest. */
213 maybe_do_interrupt(cpu);
214
215 /* All long-lived kernel loops need to check with this horrible
216 * thing called the freezer. If the Host is trying to suspend,
217 * it stops us. */
218 try_to_freeze();
219
220 /* Just make absolutely sure the Guest is still alive. One of
221 * those hypercalls could have been fatal, for example. */
222 if (cpu->lg->dead)
223 break;
224
225 /* If the Guest asked to be stopped, we sleep. The Guest's
226 * clock timer or LHCALL_BREAK from the Waker will wake us. */
227 if (cpu->halted) {
228 set_current_state(TASK_INTERRUPTIBLE);
229 schedule();
230 continue;
231 }
232
233 /* OK, now we're ready to jump into the Guest. First we put up
234 * the "Do Not Disturb" sign: */
235 local_irq_disable();
236
237 /* Actually run the Guest until something happens. */
238 lguest_arch_run_guest(cpu);
239
240 /* Now we're ready to be interrupted or moved to other CPUs */
241 local_irq_enable();
242
243 /* Now we deal with whatever happened to the Guest. */
244 lguest_arch_handle_trap(cpu);
245 }
246
247 /* Special case: Guest is 'dead' but wants a reboot. */
248 if (cpu->lg->dead == ERR_PTR(-ERESTART))
249 return -ERESTART;
250
251 /* The Guest is dead => "No such file or directory" */
252 return -ENOENT;
253 }
254
255 /*H:000
256 * Welcome to the Host!
257 *
258 * By this point your brain has been tickled by the Guest code and numbed by
259 * the Launcher code; prepare for it to be stretched by the Host code. This is
260 * the heart. Let's begin at the initialization routine for the Host's lg
261 * module.
262 */
263 static int __init init(void)
264 {
265 int err;
266
267 /* Lguest can't run under Xen, VMI or itself. It does Tricky Stuff. */
268 if (paravirt_enabled()) {
269 printk("lguest is afraid of being a guest\n");
270 return -EPERM;
271 }
272
273 /* First we put the Switcher up in very high virtual memory. */
274 err = map_switcher();
275 if (err)
276 goto out;
277
278 /* Now we set up the pagetable implementation for the Guests. */
279 err = init_pagetables(switcher_page, SHARED_SWITCHER_PAGES);
280 if (err)
281 goto unmap;
282
283 /* We might need to reserve an interrupt vector. */
284 err = init_interrupts();
285 if (err)
286 goto free_pgtables;
287
288 /* /dev/lguest needs to be registered. */
289 err = lguest_device_init();
290 if (err)
291 goto free_interrupts;
292
293 /* Finally we do some architecture-specific setup. */
294 lguest_arch_host_init();
295
296 /* All good! */
297 return 0;
298
299 free_interrupts:
300 free_interrupts();
301 free_pgtables:
302 free_pagetables();
303 unmap:
304 unmap_switcher();
305 out:
306 return err;
307 }
308
309 /* Cleaning up is just the same code, backwards. With a little French. */
310 static void __exit fini(void)
311 {
312 lguest_device_remove();
313 free_interrupts();
314 free_pagetables();
315 unmap_switcher();
316
317 lguest_arch_host_fini();
318 }
319 /*:*/
320
321 /* The Host side of lguest can be a module. This is a nice way for people to
322 * play with it. */
323 module_init(init);
324 module_exit(fini);
325 MODULE_LICENSE("GPL");
326 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
327
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