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
 23
 24static struct vm_struct *switcher_vma;
 25static struct page **switcher_page;
 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	struct page **pagep;
 46
 47	/*
 48	 * Map the Switcher in to high memory.
 49	 *
 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.
 53	 */
 54
 55	/*
 56	 * We allocate an array of struct page pointers.  map_vm_area() wants
 57	 * this, rather than just an array of pages.
 58	 */
 59	switcher_page = kmalloc(sizeof(switcher_page[0])*TOTAL_SWITCHER_PAGES,
 60				GFP_KERNEL);
 61	if (!switcher_page) {
 62		err = -ENOMEM;
 63		goto out;
 64	}
 65
 66	/*
 67	 * Now we actually allocate the pages.  The Guest will see these pages,
 68	 * so we make sure they're zeroed.
 69	 */
 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;
 75		}
 76	}
 77
 78	/*
 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.
 82	 */
 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;
 87	}
 88
 89	/*
 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.
 94	 */
 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;
102	}
103
104	/*
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.
110	 */
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;
116	}
117
118	/*
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).
121	 */
122	memcpy(switcher_vma->addr, start_switcher_text,
123	       end_switcher_text - start_switcher_text);
124
125	printk(KERN_INFO "lguest: mapped switcher at %p\n",
126	       switcher_vma->addr);
127	/* And we succeeded... */
128	return 0;
129
130free_vma:
131	vunmap(switcher_vma->addr);
132free_pages:
133	i = TOTAL_SWITCHER_PAGES;
134free_some_pages:
135	for (--i; i >= 0; i--)
136		__free_pages(switcher_page[i], 0);
137	kfree(switcher_page);
138out:
139	return err;
140}
141/*:*/
142
143/* Cleaning up the mapping when the module is unloaded is almost... too easy. */
144static void unmap_switcher(void)
145{
146	unsigned int i;
147
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);
154}
155
156/*H:032
157 * Dealing With Guest Memory.
158 *
159 * Before we go too much further into the Host, we need to grok the routines
160 * we use to deal with Guest memory.
161 *
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.
165 *
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.
170 */
171bool lguest_address_ok(const struct lguest *lg,
172		       unsigned long addr, unsigned long len)
173{
174	return (addr+len) / PAGE_SIZE < lg->pfn_limit && (addr+len >= addr);
175}
176
177/*
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.
181 */
182void __lgread(struct lg_cpu *cpu, void *b, unsigned long addr, unsigned bytes)
183{
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);
189	}
190}
191
192/* This is the write (copy into Guest) version. */
193void __lgwrite(struct lg_cpu *cpu, unsigned long addr, const void *b,
194	       unsigned bytes)
195{
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);
199}
200/*:*/
201
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.
206 */
207int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
208{
209	/* We stop running once the Guest is dead. */
210	while (!cpu->lg->dead) {
211		unsigned int irq;
212		bool more;
213
214		/* First we run any hypercalls the Guest wants done. */
215		if (cpu->hcall)
216			do_hypercalls(cpu);
217
218		/*
219		 * It's possible the Guest did a NOTIFY hypercall to the
220		 * Launcher.
221		 */
222		if (cpu->pending_notify) {
223			/*
224			 * Does it just needs to write to a registered
225			 * eventfd (ie. the appropriate virtqueue thread)?
226			 */
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);
232			}
233		}
234
235		/*
236		 * All long-lived kernel loops need to check with this horrible
237		 * thing called the freezer.  If the Host is trying to suspend,
238		 * it stops us.
239		 */
240		try_to_freeze();
241
242		/* Check for signals */
243		if (signal_pending(current))
244			return -ERESTARTSYS;
245
246		/*
247		 * Check if there are any interrupts which can be delivered now:
248		 * if so, this sets up the hander to be executed when we next
249		 * run the Guest.
250		 */
251		irq = interrupt_pending(cpu, &more);
252		if (irq < LGUEST_IRQS)
253			try_deliver_interrupt(cpu, irq, more);
254
255		/*
256		 * Just make absolutely sure the Guest is still alive.  One of
257		 * those hypercalls could have been fatal, for example.
258		 */
259		if (cpu->lg->dead)
260			break;
261
262		/*
263		 * If the Guest asked to be stopped, we sleep.  The Guest's
264		 * clock timer will wake us.
265		 */
266		if (cpu->halted) {
267			set_current_state(TASK_INTERRUPTIBLE);
268			/*
269			 * Just before we sleep, make sure no interrupt snuck in
270			 * which we should be doing.
271			 */
272			if (interrupt_pending(cpu, &more) < LGUEST_IRQS)
273				set_current_state(TASK_RUNNING);
274			else
275				schedule();
276			continue;
277		}
278
279		/*
280		 * OK, now we're ready to jump into the Guest.  First we put up
281		 * the "Do Not Disturb" sign:
282		 */
283		local_irq_disable();
284
285		/* Actually run the Guest until something happens. */
286		lguest_arch_run_guest(cpu);
287
288		/* Now we're ready to be interrupted or moved to other CPUs */
289		local_irq_enable();
290
291		/* Now we deal with whatever happened to the Guest. */
292		lguest_arch_handle_trap(cpu);
293	}
294
295	/* Special case: Guest is 'dead' but wants a reboot. */
296	if (cpu->lg->dead == ERR_PTR(-ERESTART))
297		return -ERESTART;
298
299	/* The Guest is dead => "No such file or directory" */
300	return -ENOENT;
301}
302
303/*H:000
304 * Welcome to the Host!
305 *
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.
310 */
311static int __init init(void)
312{
313	int err;
314
315	/* Lguest can't run under Xen, VMI or itself.  It does Tricky Stuff. */
316	if (get_kernel_rpl() != 0) {
317		printk("lguest is afraid of being a guest\n");
318		return -EPERM;
319	}
320
321	/* First we put the Switcher up in very high virtual memory. */
322	err = map_switcher();
323	if (err)
324		goto out;
325
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;
330
331	/* We might need to reserve an interrupt vector. */
332	err = init_interrupts();
333	if (err)
334		goto free_pgtables;
335
336	/* /dev/lguest needs to be registered. */
337	err = lguest_device_init();
338	if (err)
339		goto free_interrupts;
340
341	/* Finally we do some architecture-specific setup. */
342	lguest_arch_host_init();
343
344	/* All good! */
345	return 0;
346
347free_interrupts:
348	free_interrupts();
349free_pgtables:
350	free_pagetables();
351unmap:
352	unmap_switcher();
353out:
354	return err;
355}
356
357/* Cleaning up is just the same code, backwards.  With a little French. */
358static void __exit fini(void)
359{
360	lguest_device_remove();
361	free_interrupts();
362	free_pagetables();
363	unmap_switcher();
364
365	lguest_arch_host_fini();
366}
367/*:*/
368
369/*
370 * The Host side of lguest can be a module.  This is a nice way for people to
371 * play with it.
372 */
373module_init(init);
374module_exit(fini);
375MODULE_LICENSE("GPL");
376MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");