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.
6 #include <linux/module.h>
7 #include <linux/stringify.h>
8 #include <linux/stddef.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>
20 #include <asm/asm-offsets.h>
23 unsigned long switcher_addr
;
24 struct page
**lg_switcher_pages
;
25 static struct vm_struct
*switcher_vma
;
27 /* This One Big lock protects all inter-guest data structures. */
28 DEFINE_MUTEX(lguest_lock
);
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
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)
47 * Map the Switcher in to high memory.
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
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
);
62 * We allocate an array of struct page pointers. map_vm_area() wants
63 * this, rather than just an array of pages.
65 lg_switcher_pages
= kmalloc(sizeof(lg_switcher_pages
[0])
66 * TOTAL_SWITCHER_PAGES
,
68 if (!lg_switcher_pages
) {
74 * Now we actually allocate the pages. The Guest will see these pages,
75 * so we make sure they're zeroed.
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
]) {
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.
91 switcher_addr
= FIXADDR_START
- (TOTAL_SWITCHER_PAGES
+1)*PAGE_SIZE
;
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.
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
);
104 printk("lguest: could not map switcher pages high\n");
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.
114 err
= map_vm_area(switcher_vma
, PAGE_KERNEL_EXEC
, lg_switcher_pages
);
116 printk("lguest: map_vm_area failed: %i\n", err
);
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).
124 memcpy(switcher_vma
->addr
, start_switcher_text
,
125 end_switcher_text
- start_switcher_text
);
127 printk(KERN_INFO
"lguest: mapped switcher at %p\n",
129 /* And we succeeded... */
133 vunmap(switcher_vma
->addr
);
135 i
= TOTAL_SWITCHER_PAGES
;
137 for (--i
; i
>= 0; i
--)
138 __free_pages(lg_switcher_pages
[i
], 0);
139 kfree(lg_switcher_pages
);
145 /* Cleaning up the mapping when the module is unloaded is almost... too easy. */
146 static void unmap_switcher(void)
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
);
159 * Dealing With Guest Memory.
161 * Before we go too much further into the Host, we need to grok the routines
162 * we use to deal with Guest memory.
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.
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.
173 bool lguest_address_ok(const struct lguest
*lg
,
174 unsigned long addr
, unsigned long len
)
176 return addr
+len
<= lg
->pfn_limit
* PAGE_SIZE
&& (addr
+len
>= addr
);
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.
184 void __lgread(struct lg_cpu
*cpu
, void *b
, unsigned long addr
, unsigned bytes
)
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... */
190 kill_guest(cpu
, "bad read address %#lx len %u", addr
, bytes
);
194 /* This is the write (copy into Guest) version. */
195 void __lgwrite(struct lg_cpu
*cpu
, unsigned long addr
, const void *b
,
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
);
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.
209 int run_guest(struct lg_cpu
*cpu
, unsigned long __user
*user
)
211 /* If the launcher asked for a register with LHREQ_GETREG */
213 if (put_user(*cpu
->reg_read
, user
))
215 cpu
->reg_read
= NULL
;
216 return sizeof(*cpu
->reg_read
);
219 /* We stop running once the Guest is dead. */
220 while (!cpu
->lg
->dead
) {
224 /* First we run any hypercalls the Guest wants done. */
228 /* Do we have to tell the Launcher about a trap? */
229 if (cpu
->pending
.trap
) {
230 if (copy_to_user(user
, &cpu
->pending
,
231 sizeof(cpu
->pending
)))
233 return sizeof(cpu
->pending
);
237 * All long-lived kernel loops need to check with this horrible
238 * thing called the freezer. If the Host is trying to suspend,
243 /* Check for signals */
244 if (signal_pending(current
))
248 * Check if there are any interrupts which can be delivered now:
249 * if so, this sets up the hander to be executed when we next
252 irq
= interrupt_pending(cpu
, &more
);
253 if (irq
< LGUEST_IRQS
)
254 try_deliver_interrupt(cpu
, irq
, more
);
257 * Just make absolutely sure the Guest is still alive. One of
258 * those hypercalls could have been fatal, for example.
264 * If the Guest asked to be stopped, we sleep. The Guest's
265 * clock timer will wake us.
268 set_current_state(TASK_INTERRUPTIBLE
);
270 * Just before we sleep, make sure no interrupt snuck in
271 * which we should be doing.
273 if (interrupt_pending(cpu
, &more
) < LGUEST_IRQS
)
274 set_current_state(TASK_RUNNING
);
281 * OK, now we're ready to jump into the Guest. First we put up
282 * the "Do Not Disturb" sign:
286 /* Actually run the Guest until something happens. */
287 lguest_arch_run_guest(cpu
);
289 /* Now we're ready to be interrupted or moved to other CPUs */
292 /* Now we deal with whatever happened to the Guest. */
293 lguest_arch_handle_trap(cpu
);
296 /* Special case: Guest is 'dead' but wants a reboot. */
297 if (cpu
->lg
->dead
== ERR_PTR(-ERESTART
))
300 /* The Guest is dead => "No such file or directory" */
305 * Welcome to the Host!
307 * By this point your brain has been tickled by the Guest code and numbed by
308 * the Launcher code; prepare for it to be stretched by the Host code. This is
309 * the heart. Let's begin at the initialization routine for the Host's lg
312 static int __init
init(void)
316 /* Lguest can't run under Xen, VMI or itself. It does Tricky Stuff. */
317 if (get_kernel_rpl() != 0) {
318 printk("lguest is afraid of being a guest\n");
322 /* First we put the Switcher up in very high virtual memory. */
323 err
= map_switcher();
327 /* We might need to reserve an interrupt vector. */
328 err
= init_interrupts();
332 /* /dev/lguest needs to be registered. */
333 err
= lguest_device_init();
335 goto free_interrupts
;
337 /* Finally we do some architecture-specific setup. */
338 lguest_arch_host_init();
351 /* Cleaning up is just the same code, backwards. With a little French. */
352 static void __exit
fini(void)
354 lguest_device_remove();
358 lguest_arch_host_fini();
363 * The Host side of lguest can be a module. This is a nice way for people to
368 MODULE_LICENSE("GPL");
369 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
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