![Rusty Russell](/assets/img/avatar_default.png)
1) This allows us to get alot closer to booting bzImages. 2) It means we don't have to know page_offset. 3) The Guest needs to modify the boot pagetables to create the PAGE_OFFSET mapping before jumping to C code. 4) guest_pa() walks the page tables rather than using page_offset. 5) We don't use page_offset to figure out whether to emulate: it was always kinda quesationable, and won't work for instructions done before remapping (bzImage unpacking in particular). 6) We still want the kernel address for tlb flushing: have the initial hypercall give us that, too. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
340 lines
11 KiB
C
340 lines
11 KiB
C
/*P:200 This contains all the /dev/lguest code, whereby the userspace launcher
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* controls and communicates with the Guest. For example, the first write will
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* tell us the Guest's memory layout, pagetable, entry point and kernel address
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* offset. A read will run the Guest until something happens, such as a signal
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* or the Guest doing a DMA out to the Launcher. Writes are also used to get a
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* DMA buffer registered by the Guest and to send the Guest an interrupt. :*/
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#include <linux/uaccess.h>
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#include <linux/miscdevice.h>
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#include <linux/fs.h>
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#include "lg.h"
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/*L:310 To send DMA into the Guest, the Launcher needs to be able to ask for a
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* DMA buffer. This is done by writing LHREQ_GETDMA and the key to
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* /dev/lguest. */
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static long user_get_dma(struct lguest *lg, const unsigned long __user *input)
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{
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unsigned long key, udma, irq;
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/* Fetch the key they wrote to us. */
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if (get_user(key, input) != 0)
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return -EFAULT;
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/* Look for a free Guest DMA buffer bound to that key. */
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udma = get_dma_buffer(lg, key, &irq);
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if (!udma)
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return -ENOENT;
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/* We need to tell the Launcher what interrupt the Guest expects after
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* the buffer is filled. We stash it in udma->used_len. */
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lgwrite_u32(lg, udma + offsetof(struct lguest_dma, used_len), irq);
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/* The (guest-physical) address of the DMA buffer is returned from
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* the write(). */
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return udma;
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}
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/*L:315 To force the Guest to stop running and return to the Launcher, the
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* Waker sets writes LHREQ_BREAK and the value "1" to /dev/lguest. The
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* Launcher then writes LHREQ_BREAK and "0" to release the Waker. */
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static int break_guest_out(struct lguest *lg, const unsigned long __user *input)
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{
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unsigned long on;
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/* Fetch whether they're turning break on or off.. */
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if (get_user(on, input) != 0)
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return -EFAULT;
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if (on) {
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lg->break_out = 1;
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/* Pop it out (may be running on different CPU) */
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wake_up_process(lg->tsk);
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/* Wait for them to reset it */
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return wait_event_interruptible(lg->break_wq, !lg->break_out);
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} else {
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lg->break_out = 0;
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wake_up(&lg->break_wq);
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return 0;
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}
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}
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/*L:050 Sending an interrupt is done by writing LHREQ_IRQ and an interrupt
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* number to /dev/lguest. */
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static int user_send_irq(struct lguest *lg, const unsigned long __user *input)
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{
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unsigned long irq;
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if (get_user(irq, input) != 0)
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return -EFAULT;
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if (irq >= LGUEST_IRQS)
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return -EINVAL;
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/* Next time the Guest runs, the core code will see if it can deliver
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* this interrupt. */
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set_bit(irq, lg->irqs_pending);
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return 0;
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}
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/*L:040 Once our Guest is initialized, the Launcher makes it run by reading
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* from /dev/lguest. */
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static ssize_t read(struct file *file, char __user *user, size_t size,loff_t*o)
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{
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struct lguest *lg = file->private_data;
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/* You must write LHREQ_INITIALIZE first! */
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if (!lg)
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return -EINVAL;
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/* If you're not the task which owns the guest, go away. */
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if (current != lg->tsk)
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return -EPERM;
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/* If the guest is already dead, we indicate why */
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if (lg->dead) {
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size_t len;
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/* lg->dead either contains an error code, or a string. */
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if (IS_ERR(lg->dead))
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return PTR_ERR(lg->dead);
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/* We can only return as much as the buffer they read with. */
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len = min(size, strlen(lg->dead)+1);
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if (copy_to_user(user, lg->dead, len) != 0)
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return -EFAULT;
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return len;
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}
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/* If we returned from read() last time because the Guest sent DMA,
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* clear the flag. */
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if (lg->dma_is_pending)
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lg->dma_is_pending = 0;
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/* Run the Guest until something interesting happens. */
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return run_guest(lg, (unsigned long __user *)user);
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}
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/*L:020 The initialization write supplies 4 pointer sized (32 or 64 bit)
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* values (in addition to the LHREQ_INITIALIZE value). These are:
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*
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* base: The start of the Guest-physical memory inside the Launcher memory.
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*
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* pfnlimit: The highest (Guest-physical) page number the Guest should be
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* allowed to access. The Launcher has to live in Guest memory, so it sets
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* this to ensure the Guest can't reach it.
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*
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* pgdir: The (Guest-physical) address of the top of the initial Guest
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* pagetables (which are set up by the Launcher).
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*
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* start: The first instruction to execute ("eip" in x86-speak).
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*/
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static int initialize(struct file *file, const unsigned long __user *input)
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{
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/* "struct lguest" contains everything we (the Host) know about a
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* Guest. */
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struct lguest *lg;
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int err;
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unsigned long args[4];
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/* We grab the Big Lguest lock, which protects against multiple
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* simultaneous initializations. */
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mutex_lock(&lguest_lock);
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/* You can't initialize twice! Close the device and start again... */
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if (file->private_data) {
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err = -EBUSY;
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goto unlock;
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}
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if (copy_from_user(args, input, sizeof(args)) != 0) {
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err = -EFAULT;
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goto unlock;
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}
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lg = kzalloc(sizeof(*lg), GFP_KERNEL);
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if (!lg) {
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err = -ENOMEM;
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goto unlock;
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}
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/* Populate the easy fields of our "struct lguest" */
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lg->mem_base = (void __user *)(long)args[0];
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lg->pfn_limit = args[1];
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/* We need a complete page for the Guest registers: they are accessible
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* to the Guest and we can only grant it access to whole pages. */
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lg->regs_page = get_zeroed_page(GFP_KERNEL);
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if (!lg->regs_page) {
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err = -ENOMEM;
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goto release_guest;
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}
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/* We actually put the registers at the bottom of the page. */
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lg->regs = (void *)lg->regs_page + PAGE_SIZE - sizeof(*lg->regs);
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/* Initialize the Guest's shadow page tables, using the toplevel
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* address the Launcher gave us. This allocates memory, so can
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* fail. */
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err = init_guest_pagetable(lg, args[2]);
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if (err)
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goto free_regs;
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/* Now we initialize the Guest's registers, handing it the start
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* address. */
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lguest_arch_setup_regs(lg, args[3]);
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/* The timer for lguest's clock needs initialization. */
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init_clockdev(lg);
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/* We keep a pointer to the Launcher task (ie. current task) for when
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* other Guests want to wake this one (inter-Guest I/O). */
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lg->tsk = current;
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/* We need to keep a pointer to the Launcher's memory map, because if
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* the Launcher dies we need to clean it up. If we don't keep a
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* reference, it is destroyed before close() is called. */
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lg->mm = get_task_mm(lg->tsk);
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/* Initialize the queue for the waker to wait on */
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init_waitqueue_head(&lg->break_wq);
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/* We remember which CPU's pages this Guest used last, for optimization
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* when the same Guest runs on the same CPU twice. */
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lg->last_pages = NULL;
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/* We keep our "struct lguest" in the file's private_data. */
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file->private_data = lg;
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mutex_unlock(&lguest_lock);
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/* And because this is a write() call, we return the length used. */
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return sizeof(args);
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free_regs:
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free_page(lg->regs_page);
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release_guest:
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memset(lg, 0, sizeof(*lg));
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unlock:
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mutex_unlock(&lguest_lock);
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return err;
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}
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/*L:010 The first operation the Launcher does must be a write. All writes
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* start with a 32 bit number: for the first write this must be
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* LHREQ_INITIALIZE to set up the Guest. After that the Launcher can use
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* writes of other values to get DMA buffers and send interrupts. */
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static ssize_t write(struct file *file, const char __user *in,
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size_t size, loff_t *off)
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{
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/* Once the guest is initialized, we hold the "struct lguest" in the
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* file private data. */
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struct lguest *lg = file->private_data;
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const unsigned long __user *input = (const unsigned long __user *)in;
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unsigned long req;
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if (get_user(req, input) != 0)
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return -EFAULT;
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input++;
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/* If you haven't initialized, you must do that first. */
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if (req != LHREQ_INITIALIZE && !lg)
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return -EINVAL;
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/* Once the Guest is dead, all you can do is read() why it died. */
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if (lg && lg->dead)
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return -ENOENT;
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/* If you're not the task which owns the Guest, you can only break */
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if (lg && current != lg->tsk && req != LHREQ_BREAK)
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return -EPERM;
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switch (req) {
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case LHREQ_INITIALIZE:
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return initialize(file, input);
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case LHREQ_GETDMA:
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return user_get_dma(lg, input);
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case LHREQ_IRQ:
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return user_send_irq(lg, input);
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case LHREQ_BREAK:
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return break_guest_out(lg, input);
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default:
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return -EINVAL;
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}
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}
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/*L:060 The final piece of interface code is the close() routine. It reverses
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* everything done in initialize(). This is usually called because the
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* Launcher exited.
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*
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* Note that the close routine returns 0 or a negative error number: it can't
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* really fail, but it can whine. I blame Sun for this wart, and K&R C for
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* letting them do it. :*/
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static int close(struct inode *inode, struct file *file)
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{
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struct lguest *lg = file->private_data;
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/* If we never successfully initialized, there's nothing to clean up */
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if (!lg)
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return 0;
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/* We need the big lock, to protect from inter-guest I/O and other
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* Launchers initializing guests. */
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mutex_lock(&lguest_lock);
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/* Cancels the hrtimer set via LHCALL_SET_CLOCKEVENT. */
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hrtimer_cancel(&lg->hrt);
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/* Free any DMA buffers the Guest had bound. */
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release_all_dma(lg);
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/* Free up the shadow page tables for the Guest. */
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free_guest_pagetable(lg);
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/* Now all the memory cleanups are done, it's safe to release the
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* Launcher's memory management structure. */
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mmput(lg->mm);
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/* If lg->dead doesn't contain an error code it will be NULL or a
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* kmalloc()ed string, either of which is ok to hand to kfree(). */
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if (!IS_ERR(lg->dead))
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kfree(lg->dead);
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/* We can free up the register page we allocated. */
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free_page(lg->regs_page);
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/* We clear the entire structure, which also marks it as free for the
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* next user. */
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memset(lg, 0, sizeof(*lg));
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/* Release lock and exit. */
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mutex_unlock(&lguest_lock);
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return 0;
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}
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/*L:000
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* Welcome to our journey through the Launcher!
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*
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* The Launcher is the Host userspace program which sets up, runs and services
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* the Guest. In fact, many comments in the Drivers which refer to "the Host"
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* doing things are inaccurate: the Launcher does all the device handling for
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* the Guest. The Guest can't tell what's done by the the Launcher and what by
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* the Host.
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*
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* Just to confuse you: to the Host kernel, the Launcher *is* the Guest and we
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* shall see more of that later.
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*
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* We begin our understanding with the Host kernel interface which the Launcher
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* uses: reading and writing a character device called /dev/lguest. All the
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* work happens in the read(), write() and close() routines: */
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static struct file_operations lguest_fops = {
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.owner = THIS_MODULE,
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.release = close,
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.write = write,
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.read = read,
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};
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/* This is a textbook example of a "misc" character device. Populate a "struct
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* miscdevice" and register it with misc_register(). */
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static struct miscdevice lguest_dev = {
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.minor = MISC_DYNAMIC_MINOR,
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.name = "lguest",
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.fops = &lguest_fops,
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};
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int __init lguest_device_init(void)
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{
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return misc_register(&lguest_dev);
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}
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void __exit lguest_device_remove(void)
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{
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misc_deregister(&lguest_dev);
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}
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