Root/drivers/lguest/core.c

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>");
377

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