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>
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
);
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)
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
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
,
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
]) {
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
){
85 printk("lguest: mapping switcher would thwack fixmap\n");
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
);
100 printk("lguest: could not map switcher pages high\n");
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
111 pagep
= switcher_page
;
112 err
= map_vm_area(switcher_vma
, PAGE_KERNEL_EXEC
, &pagep
);
114 printk("lguest: map_vm_area failed: %i\n", err
);
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",
127 /* And we succeeded... */
131 vunmap(switcher_vma
->addr
);
133 i
= TOTAL_SWITCHER_PAGES
;
135 for (--i
; i
>= 0; i
--)
136 __free_pages(switcher_page
[i
], 0);
137 kfree(switcher_page
);
143 /* Cleaning up the mapping when the module is unloaded is almost... too easy. */
144 static void unmap_switcher(void)
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
);
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... */
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
,
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
);
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
) {
214 /* First we run any hypercalls the Guest wants done. */
219 * It's possible the Guest did a NOTIFY hypercall to the
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
))
231 return sizeof(cpu
->pending_notify
);
235 /* Check for signals */
236 if (signal_pending(current
))
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
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,
256 * Just make absolutely sure the Guest is still alive. One of
257 * those hypercalls could have been fatal, for example.
263 * If the Guest asked to be stopped, we sleep. The Guest's
264 * clock timer will wake us.
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
);
280 * OK, now we're ready to jump into the Guest. First we put up
281 * the "Do Not Disturb" sign:
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 */
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
))
299 /* The Guest is dead => "No such file or directory" */
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
311 static int __init
init(void)
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");
321 /* First we put the Switcher up in very high virtual memory. */
322 err
= map_switcher();
326 /* Now we set up the pagetable implementation for the Guests. */
327 err
= init_pagetables(switcher_page
, SHARED_SWITCHER_PAGES
);
331 /* We might need to reserve an interrupt vector. */
332 err
= init_interrupts();
336 /* /dev/lguest needs to be registered. */
337 err
= lguest_device_init();
339 goto free_interrupts
;
341 /* Finally we do some architecture-specific setup. */
342 lguest_arch_host_init();
357 /* Cleaning up is just the same code, backwards. With a little French. */
358 static void __exit
fini(void)
360 lguest_device_remove();
365 lguest_arch_host_fini();
370 * The Host side of lguest can be a module. This is a nice way for people to
375 MODULE_LICENSE("GPL");
376 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");