[go: nahoru, domu]
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"
22
23unsigned long switcher_addr;
24struct page **lg_switcher_pages;
25static struct vm_struct *switcher_vma;
26
27/* This One Big lock protects all inter-guest data structures. */
28DEFINE_MUTEX(lguest_lock);
29
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.
35 *
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.
38 *
39 * Trying to map memory at a particular address is an unusual thing to do, so
40 * it's not a simple one-liner.
41 */
42static __init int map_switcher(void)
43{
44	int i, err;
45
46	/*
47	 * Map the Switcher in to high memory.
48	 *
49	 * It turns out that if we choose the address 0xFFC00000 (4MB under the
50	 * top virtual address), it makes setting up the page tables really
51	 * easy.
52	 */
53
54	/* We assume Switcher text fits into a single page. */
55	if (end_switcher_text - start_switcher_text > PAGE_SIZE) {
56		printk(KERN_ERR "lguest: switcher text too large (%zu)\n",
57		       end_switcher_text - start_switcher_text);
58		return -EINVAL;
59	}
60
61	/*
62	 * We allocate an array of struct page pointers.  map_vm_area() wants
63	 * this, rather than just an array of pages.
64	 */
65	lg_switcher_pages = kmalloc(sizeof(lg_switcher_pages[0])
66				    * TOTAL_SWITCHER_PAGES,
67				    GFP_KERNEL);
68	if (!lg_switcher_pages) {
69		err = -ENOMEM;
70		goto out;
71	}
72
73	/*
74	 * Now we actually allocate the pages.  The Guest will see these pages,
75	 * so we make sure they're zeroed.
76	 */
77	for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) {
78		lg_switcher_pages[i] = alloc_page(GFP_KERNEL|__GFP_ZERO);
79		if (!lg_switcher_pages[i]) {
80			err = -ENOMEM;
81			goto free_some_pages;
82		}
83	}
84
85	/*
86	 * We place the Switcher underneath the fixmap area, which is the
87	 * highest virtual address we can get.  This is important, since we
88	 * tell the Guest it can't access this memory, so we want its ceiling
89	 * as high as possible.
90	 */
91	switcher_addr = FIXADDR_START - (TOTAL_SWITCHER_PAGES+1)*PAGE_SIZE;
92
93	/*
94	 * Now we reserve the "virtual memory area" we want.  We might
95	 * not get it in theory, but in practice it's worked so far.
96	 * The end address needs +1 because __get_vm_area allocates an
97	 * extra guard page, so we need space for that.
98	 */
99	switcher_vma = __get_vm_area(TOTAL_SWITCHER_PAGES * PAGE_SIZE,
100				     VM_ALLOC, switcher_addr, switcher_addr
101				     + (TOTAL_SWITCHER_PAGES+1) * PAGE_SIZE);
102	if (!switcher_vma) {
103		err = -ENOMEM;
104		printk("lguest: could not map switcher pages high\n");
105		goto free_pages;
106	}
107
108	/*
109	 * This code actually sets up the pages we've allocated to appear at
110	 * switcher_addr.  map_vm_area() takes the vma we allocated above, the
111	 * kind of pages we're mapping (kernel pages), and a pointer to our
112	 * array of struct pages.
113	 */
114	err = map_vm_area(switcher_vma, PAGE_KERNEL_EXEC, lg_switcher_pages);
115	if (err) {
116		printk("lguest: map_vm_area failed: %i\n", err);
117		goto free_vma;
118	}
119
120	/*
121	 * Now the Switcher is mapped at the right address, we can't fail!
122	 * Copy in the compiled-in Switcher code (from x86/switcher_32.S).
123	 */
124	memcpy(switcher_vma->addr, start_switcher_text,
125	       end_switcher_text - start_switcher_text);
126
127	printk(KERN_INFO "lguest: mapped switcher at %p\n",
128	       switcher_vma->addr);
129	/* And we succeeded... */
130	return 0;
131
132free_vma:
133	vunmap(switcher_vma->addr);
134free_pages:
135	i = TOTAL_SWITCHER_PAGES;
136free_some_pages:
137	for (--i; i >= 0; i--)
138		__free_pages(lg_switcher_pages[i], 0);
139	kfree(lg_switcher_pages);
140out:
141	return err;
142}
143/*:*/
144
145/* Cleaning up the mapping when the module is unloaded is almost... too easy. */
146static void unmap_switcher(void)
147{
148	unsigned int i;
149
150	/* vunmap() undoes *both* map_vm_area() and __get_vm_area(). */
151	vunmap(switcher_vma->addr);
152	/* Now we just need to free the pages we copied the switcher into */
153	for (i = 0; i < TOTAL_SWITCHER_PAGES; i++)
154		__free_pages(lg_switcher_pages[i], 0);
155	kfree(lg_switcher_pages);
156}
157
158/*H:032
159 * Dealing With Guest Memory.
160 *
161 * Before we go too much further into the Host, we need to grok the routines
162 * we use to deal with Guest memory.
163 *
164 * When the Guest gives us (what it thinks is) a physical address, we can use
165 * the normal copy_from_user() & copy_to_user() on the corresponding place in
166 * the memory region allocated by the Launcher.
167 *
168 * But we can't trust the Guest: it might be trying to access the Launcher
169 * code.  We have to check that the range is below the pfn_limit the Launcher
170 * gave us.  We have to make sure that addr + len doesn't give us a false
171 * positive by overflowing, too.
172 */
173bool lguest_address_ok(const struct lguest *lg,
174		       unsigned long addr, unsigned long len)
175{
176	return (addr+len) / PAGE_SIZE < lg->pfn_limit && (addr+len >= addr);
177}
178
179/*
180 * This routine copies memory from the Guest.  Here we can see how useful the
181 * kill_lguest() routine we met in the Launcher can be: we return a random
182 * value (all zeroes) instead of needing to return an error.
183 */
184void __lgread(struct lg_cpu *cpu, void *b, unsigned long addr, unsigned bytes)
185{
186	if (!lguest_address_ok(cpu->lg, addr, bytes)
187	    || copy_from_user(b, cpu->lg->mem_base + addr, bytes) != 0) {
188		/* copy_from_user should do this, but as we rely on it... */
189		memset(b, 0, bytes);
190		kill_guest(cpu, "bad read address %#lx len %u", addr, bytes);
191	}
192}
193
194/* This is the write (copy into Guest) version. */
195void __lgwrite(struct lg_cpu *cpu, unsigned long addr, const void *b,
196	       unsigned bytes)
197{
198	if (!lguest_address_ok(cpu->lg, addr, bytes)
199	    || copy_to_user(cpu->lg->mem_base + addr, b, bytes) != 0)
200		kill_guest(cpu, "bad write address %#lx len %u", addr, bytes);
201}
202/*:*/
203
204/*H:030
205 * Let's jump straight to the the main loop which runs the Guest.
206 * Remember, this is called by the Launcher reading /dev/lguest, and we keep
207 * going around and around until something interesting happens.
208 */
209int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
210{
211	/* We stop running once the Guest is dead. */
212	while (!cpu->lg->dead) {
213		unsigned int irq;
214		bool more;
215
216		/* First we run any hypercalls the Guest wants done. */
217		if (cpu->hcall)
218			do_hypercalls(cpu);
219
220		/*
221		 * It's possible the Guest did a NOTIFY hypercall to the
222		 * Launcher.
223		 */
224		if (cpu->pending_notify) {
225			/*
226			 * Does it just needs to write to a registered
227			 * eventfd (ie. the appropriate virtqueue thread)?
228			 */
229			if (!send_notify_to_eventfd(cpu)) {
230				/* OK, we tell the main Launcher. */
231				if (put_user(cpu->pending_notify, user))
232					return -EFAULT;
233				return sizeof(cpu->pending_notify);
234			}
235		}
236
237		/*
238		 * All long-lived kernel loops need to check with this horrible
239		 * thing called the freezer.  If the Host is trying to suspend,
240		 * it stops us.
241		 */
242		try_to_freeze();
243
244		/* Check for signals */
245		if (signal_pending(current))
246			return -ERESTARTSYS;
247
248		/*
249		 * Check if there are any interrupts which can be delivered now:
250		 * if so, this sets up the hander to be executed when we next
251		 * run the Guest.
252		 */
253		irq = interrupt_pending(cpu, &more);
254		if (irq < LGUEST_IRQS)
255			try_deliver_interrupt(cpu, irq, more);
256
257		/*
258		 * Just make absolutely sure the Guest is still alive.  One of
259		 * those hypercalls could have been fatal, for example.
260		 */
261		if (cpu->lg->dead)
262			break;
263
264		/*
265		 * If the Guest asked to be stopped, we sleep.  The Guest's
266		 * clock timer will wake us.
267		 */
268		if (cpu->halted) {
269			set_current_state(TASK_INTERRUPTIBLE);
270			/*
271			 * Just before we sleep, make sure no interrupt snuck in
272			 * which we should be doing.
273			 */
274			if (interrupt_pending(cpu, &more) < LGUEST_IRQS)
275				set_current_state(TASK_RUNNING);
276			else
277				schedule();
278			continue;
279		}
280
281		/*
282		 * OK, now we're ready to jump into the Guest.  First we put up
283		 * the "Do Not Disturb" sign:
284		 */
285		local_irq_disable();
286
287		/* Actually run the Guest until something happens. */
288		lguest_arch_run_guest(cpu);
289
290		/* Now we're ready to be interrupted or moved to other CPUs */
291		local_irq_enable();
292
293		/* Now we deal with whatever happened to the Guest. */
294		lguest_arch_handle_trap(cpu);
295	}
296
297	/* Special case: Guest is 'dead' but wants a reboot. */
298	if (cpu->lg->dead == ERR_PTR(-ERESTART))
299		return -ERESTART;
300
301	/* The Guest is dead => "No such file or directory" */
302	return -ENOENT;
303}
304
305/*H:000
306 * Welcome to the Host!
307 *
308 * By this point your brain has been tickled by the Guest code and numbed by
309 * the Launcher code; prepare for it to be stretched by the Host code.  This is
310 * the heart.  Let's begin at the initialization routine for the Host's lg
311 * module.
312 */
313static int __init init(void)
314{
315	int err;
316
317	/* Lguest can't run under Xen, VMI or itself.  It does Tricky Stuff. */
318	if (get_kernel_rpl() != 0) {
319		printk("lguest is afraid of being a guest\n");
320		return -EPERM;
321	}
322
323	/* First we put the Switcher up in very high virtual memory. */
324	err = map_switcher();
325	if (err)
326		goto out;
327
328	/* We might need to reserve an interrupt vector. */
329	err = init_interrupts();
330	if (err)
331		goto unmap;
332
333	/* /dev/lguest needs to be registered. */
334	err = lguest_device_init();
335	if (err)
336		goto free_interrupts;
337
338	/* Finally we do some architecture-specific setup. */
339	lguest_arch_host_init();
340
341	/* All good! */
342	return 0;
343
344free_interrupts:
345	free_interrupts();
346unmap:
347	unmap_switcher();
348out:
349	return err;
350}
351
352/* Cleaning up is just the same code, backwards.  With a little French. */
353static void __exit fini(void)
354{
355	lguest_device_remove();
356	free_interrupts();
357	unmap_switcher();
358
359	lguest_arch_host_fini();
360}
361/*:*/
362
363/*
364 * The Host side of lguest can be a module.  This is a nice way for people to
365 * play with it.
366 */
367module_init(init);
368module_exit(fini);
369MODULE_LICENSE("GPL");
370MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
371