lguest: update comments
[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / drivers / lguest / core.c
blob2535933c49f83cb9fa8b7488caddf6a20dd8db09
1 /*P:400
2 * This contains run_guest() which actually calls into the Host<->Guest
3 * Switcher and analyzes the return, such as determining if the Guest wants the
4 * Host to do something. This file also contains useful helper routines.
5 :*/
6 #include <linux/module.h>
7 #include <linux/stringify.h>
8 #include <linux/stddef.h>
9 #include <linux/io.h>
10 #include <linux/mm.h>
11 #include <linux/vmalloc.h>
12 #include <linux/cpu.h>
13 #include <linux/freezer.h>
14 #include <linux/highmem.h>
15 #include <linux/slab.h>
16 #include <asm/paravirt.h>
17 #include <asm/pgtable.h>
18 #include <asm/uaccess.h>
19 #include <asm/poll.h>
20 #include <asm/asm-offsets.h>
21 #include "lg.h"
24 static struct vm_struct *switcher_vma;
25 static struct page **switcher_page;
27 /* This One Big lock protects all inter-guest data structures. */
28 DEFINE_MUTEX(lguest_lock);
30 /*H:010
31 * We need to set up the Switcher at a high virtual address. Remember the
32 * Switcher is a few hundred bytes of assembler code which actually changes the
33 * CPU to run the Guest, and then changes back to the Host when a trap or
34 * interrupt happens.
36 * The Switcher code must be at the same virtual address in the Guest as the
37 * Host since it will be running as the switchover occurs.
39 * Trying to map memory at a particular address is an unusual thing to do, so
40 * it's not a simple one-liner.
42 static __init int map_switcher(void)
44 int i, err;
45 struct page **pagep;
48 * Map the Switcher in to high memory.
50 * It turns out that if we choose the address 0xFFC00000 (4MB under the
51 * top virtual address), it makes setting up the page tables really
52 * easy.
56 * We allocate an array of struct page pointers. map_vm_area() wants
57 * this, rather than just an array of pages.
59 switcher_page = kmalloc(sizeof(switcher_page[0])*TOTAL_SWITCHER_PAGES,
60 GFP_KERNEL);
61 if (!switcher_page) {
62 err = -ENOMEM;
63 goto out;
67 * Now we actually allocate the pages. The Guest will see these pages,
68 * so we make sure they're zeroed.
70 for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) {
71 switcher_page[i] = alloc_page(GFP_KERNEL|__GFP_ZERO);
72 if (!switcher_page[i]) {
73 err = -ENOMEM;
74 goto free_some_pages;
79 * First we check that the Switcher won't overlap the fixmap area at
80 * the top of memory. It's currently nowhere near, but it could have
81 * very strange effects if it ever happened.
83 if (SWITCHER_ADDR + (TOTAL_SWITCHER_PAGES+1)*PAGE_SIZE > FIXADDR_START){
84 err = -ENOMEM;
85 printk("lguest: mapping switcher would thwack fixmap\n");
86 goto free_pages;
90 * Now we reserve the "virtual memory area" we want: 0xFFC00000
91 * (SWITCHER_ADDR). We might not get it in theory, but in practice
92 * it's worked so far. The end address needs +1 because __get_vm_area
93 * allocates an extra guard page, so we need space for that.
95 switcher_vma = __get_vm_area(TOTAL_SWITCHER_PAGES * PAGE_SIZE,
96 VM_ALLOC, SWITCHER_ADDR, SWITCHER_ADDR
97 + (TOTAL_SWITCHER_PAGES+1) * PAGE_SIZE);
98 if (!switcher_vma) {
99 err = -ENOMEM;
100 printk("lguest: could not map switcher pages high\n");
101 goto free_pages;
105 * This code actually sets up the pages we've allocated to appear at
106 * SWITCHER_ADDR. map_vm_area() takes the vma we allocated above, the
107 * kind of pages we're mapping (kernel pages), and a pointer to our
108 * array of struct pages. It increments that pointer, but we don't
109 * care.
111 pagep = switcher_page;
112 err = map_vm_area(switcher_vma, PAGE_KERNEL_EXEC, &pagep);
113 if (err) {
114 printk("lguest: map_vm_area failed: %i\n", err);
115 goto free_vma;
119 * Now the Switcher is mapped at the right address, we can't fail!
120 * Copy in the compiled-in Switcher code (from x86/switcher_32.S).
122 memcpy(switcher_vma->addr, start_switcher_text,
123 end_switcher_text - start_switcher_text);
125 printk(KERN_INFO "lguest: mapped switcher at %p\n",
126 switcher_vma->addr);
127 /* And we succeeded... */
128 return 0;
130 free_vma:
131 vunmap(switcher_vma->addr);
132 free_pages:
133 i = TOTAL_SWITCHER_PAGES;
134 free_some_pages:
135 for (--i; i >= 0; i--)
136 __free_pages(switcher_page[i], 0);
137 kfree(switcher_page);
138 out:
139 return err;
141 /*:*/
143 /* Cleaning up the mapping when the module is unloaded is almost... too easy. */
144 static void unmap_switcher(void)
146 unsigned int i;
148 /* vunmap() undoes *both* map_vm_area() and __get_vm_area(). */
149 vunmap(switcher_vma->addr);
150 /* Now we just need to free the pages we copied the switcher into */
151 for (i = 0; i < TOTAL_SWITCHER_PAGES; i++)
152 __free_pages(switcher_page[i], 0);
153 kfree(switcher_page);
156 /*H:032
157 * Dealing With Guest Memory.
159 * Before we go too much further into the Host, we need to grok the routines
160 * we use to deal with Guest memory.
162 * When the Guest gives us (what it thinks is) a physical address, we can use
163 * the normal copy_from_user() & copy_to_user() on the corresponding place in
164 * the memory region allocated by the Launcher.
166 * But we can't trust the Guest: it might be trying to access the Launcher
167 * code. We have to check that the range is below the pfn_limit the Launcher
168 * gave us. We have to make sure that addr + len doesn't give us a false
169 * positive by overflowing, too.
171 bool lguest_address_ok(const struct lguest *lg,
172 unsigned long addr, unsigned long len)
174 return (addr+len) / PAGE_SIZE < lg->pfn_limit && (addr+len >= addr);
178 * This routine copies memory from the Guest. Here we can see how useful the
179 * kill_lguest() routine we met in the Launcher can be: we return a random
180 * value (all zeroes) instead of needing to return an error.
182 void __lgread(struct lg_cpu *cpu, void *b, unsigned long addr, unsigned bytes)
184 if (!lguest_address_ok(cpu->lg, addr, bytes)
185 || copy_from_user(b, cpu->lg->mem_base + addr, bytes) != 0) {
186 /* copy_from_user should do this, but as we rely on it... */
187 memset(b, 0, bytes);
188 kill_guest(cpu, "bad read address %#lx len %u", addr, bytes);
192 /* This is the write (copy into Guest) version. */
193 void __lgwrite(struct lg_cpu *cpu, unsigned long addr, const void *b,
194 unsigned bytes)
196 if (!lguest_address_ok(cpu->lg, addr, bytes)
197 || copy_to_user(cpu->lg->mem_base + addr, b, bytes) != 0)
198 kill_guest(cpu, "bad write address %#lx len %u", addr, bytes);
200 /*:*/
202 /*H:030
203 * Let's jump straight to the the main loop which runs the Guest.
204 * Remember, this is called by the Launcher reading /dev/lguest, and we keep
205 * going around and around until something interesting happens.
207 int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
209 /* We stop running once the Guest is dead. */
210 while (!cpu->lg->dead) {
211 unsigned int irq;
212 bool more;
214 /* First we run any hypercalls the Guest wants done. */
215 if (cpu->hcall)
216 do_hypercalls(cpu);
219 * It's possible the Guest did a NOTIFY hypercall to the
220 * Launcher.
222 if (cpu->pending_notify) {
224 * Does it just needs to write to a registered
225 * eventfd (ie. the appropriate virtqueue thread)?
227 if (!send_notify_to_eventfd(cpu)) {
228 /* OK, we tell the main Laucher. */
229 if (put_user(cpu->pending_notify, user))
230 return -EFAULT;
231 return sizeof(cpu->pending_notify);
235 /* Check for signals */
236 if (signal_pending(current))
237 return -ERESTARTSYS;
240 * Check if there are any interrupts which can be delivered now:
241 * if so, this sets up the hander to be executed when we next
242 * run the Guest.
244 irq = interrupt_pending(cpu, &more);
245 if (irq < LGUEST_IRQS)
246 try_deliver_interrupt(cpu, irq, more);
249 * All long-lived kernel loops need to check with this horrible
250 * thing called the freezer. If the Host is trying to suspend,
251 * it stops us.
253 try_to_freeze();
256 * Just make absolutely sure the Guest is still alive. One of
257 * those hypercalls could have been fatal, for example.
259 if (cpu->lg->dead)
260 break;
263 * If the Guest asked to be stopped, we sleep. The Guest's
264 * clock timer will wake us.
266 if (cpu->halted) {
267 set_current_state(TASK_INTERRUPTIBLE);
269 * Just before we sleep, make sure no interrupt snuck in
270 * which we should be doing.
272 if (interrupt_pending(cpu, &more) < LGUEST_IRQS)
273 set_current_state(TASK_RUNNING);
274 else
275 schedule();
276 continue;
280 * OK, now we're ready to jump into the Guest. First we put up
281 * the "Do Not Disturb" sign:
283 local_irq_disable();
285 /* Actually run the Guest until something happens. */
286 lguest_arch_run_guest(cpu);
288 /* Now we're ready to be interrupted or moved to other CPUs */
289 local_irq_enable();
291 /* Now we deal with whatever happened to the Guest. */
292 lguest_arch_handle_trap(cpu);
295 /* Special case: Guest is 'dead' but wants a reboot. */
296 if (cpu->lg->dead == ERR_PTR(-ERESTART))
297 return -ERESTART;
299 /* The Guest is dead => "No such file or directory" */
300 return -ENOENT;
303 /*H:000
304 * Welcome to the Host!
306 * By this point your brain has been tickled by the Guest code and numbed by
307 * the Launcher code; prepare for it to be stretched by the Host code. This is
308 * the heart. Let's begin at the initialization routine for the Host's lg
309 * module.
311 static int __init init(void)
313 int err;
315 /* Lguest can't run under Xen, VMI or itself. It does Tricky Stuff. */
316 if (paravirt_enabled()) {
317 printk("lguest is afraid of being a guest\n");
318 return -EPERM;
321 /* First we put the Switcher up in very high virtual memory. */
322 err = map_switcher();
323 if (err)
324 goto out;
326 /* Now we set up the pagetable implementation for the Guests. */
327 err = init_pagetables(switcher_page, SHARED_SWITCHER_PAGES);
328 if (err)
329 goto unmap;
331 /* We might need to reserve an interrupt vector. */
332 err = init_interrupts();
333 if (err)
334 goto free_pgtables;
336 /* /dev/lguest needs to be registered. */
337 err = lguest_device_init();
338 if (err)
339 goto free_interrupts;
341 /* Finally we do some architecture-specific setup. */
342 lguest_arch_host_init();
344 /* All good! */
345 return 0;
347 free_interrupts:
348 free_interrupts();
349 free_pgtables:
350 free_pagetables();
351 unmap:
352 unmap_switcher();
353 out:
354 return err;
357 /* Cleaning up is just the same code, backwards. With a little French. */
358 static void __exit fini(void)
360 lguest_device_remove();
361 free_interrupts();
362 free_pagetables();
363 unmap_switcher();
365 lguest_arch_host_fini();
367 /*:*/
370 * The Host side of lguest can be a module. This is a nice way for people to
371 * play with it.
373 module_init(init);
374 module_exit(fini);
375 MODULE_LICENSE("GPL");
376 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");