/*P:400
 * This contains run_guest() which actually calls into the Host<->Guest
 * Switcher and analyzes the return, such as determining if the Guest wants the
 * Host to do something.  This file also contains useful helper routines.
:*/
#include <linux/module.h>
#include <linux/stringify.h>
#include <linux/stddef.h>
#include <linux/io.h>
#include <linux/mm.h>
#include <linux/sched/signal.h>
#include <linux/vmalloc.h>
#include <linux/cpu.h>
#include <linux/freezer.h>
#include <linux/highmem.h>
#include <linux/slab.h>
#include <asm/paravirt.h>
#include <asm/pgtable.h>
#include <linux/uaccess.h>
#include <asm/poll.h>
#include <asm/asm-offsets.h>
#include "lg.h"

unsigned long switcher_addr;
struct page **lg_switcher_pages;
static struct vm_struct *switcher_text_vma;
static struct vm_struct *switcher_stacks_vma;

/* This One Big lock protects all inter-guest data structures. */
DEFINE_MUTEX(lguest_lock);

/*H:010
 * We need to set up the Switcher at a high virtual address.  Remember the
 * Switcher is a few hundred bytes of assembler code which actually changes the
 * CPU to run the Guest, and then changes back to the Host when a trap or
 * interrupt happens.
 *
 * The Switcher code must be at the same virtual address in the Guest as the
 * Host since it will be running as the switchover occurs.
 *
 * Trying to map memory at a particular address is an unusual thing to do, so
 * it's not a simple one-liner.
 */
static __init int map_switcher(void)
{
        int i, err;

        /*
         * Map the Switcher in to high memory.
         *
         * It turns out that if we choose the address 0xFFC00000 (4MB under the
         * top virtual address), it makes setting up the page tables really
         * easy.
         */

        /* We assume Switcher text fits into a single page. */
        if (end_switcher_text - start_switcher_text > PAGE_SIZE) {
                printk(KERN_ERR "lguest: switcher text too large (%zu)\n",
                       end_switcher_text - start_switcher_text);
                return -EINVAL;
        }

        /*
         * We allocate an array of struct page pointers.  map_vm_area() wants
         * this, rather than just an array of pages.
         */
        lg_switcher_pages = kmalloc(sizeof(lg_switcher_pages[0])
                                    * TOTAL_SWITCHER_PAGES,
                                    GFP_KERNEL);
        if (!lg_switcher_pages) {
                err = -ENOMEM;
                goto out;
        }

        /*
         * Now we actually allocate the pages.  The Guest will see these pages,
         * so we make sure they're zeroed.
         */
        for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) {
                lg_switcher_pages[i] = alloc_page(GFP_KERNEL|__GFP_ZERO);
                if (!lg_switcher_pages[i]) {
                        err = -ENOMEM;
                        goto free_some_pages;
                }
        }

        /*
         * Copy in the compiled-in Switcher code (from x86/switcher_32.S).
         * It goes in the first page, which we map in momentarily.
         */
        memcpy(kmap(lg_switcher_pages[0]), start_switcher_text,
               end_switcher_text - start_switcher_text);
        kunmap(lg_switcher_pages[0]);

        /*
         * We place the Switcher underneath the fixmap area, which is the
         * highest virtual address we can get.  This is important, since we
         * tell the Guest it can't access this memory, so we want its ceiling
         * as high as possible.
         */
        switcher_addr = FIXADDR_START - TOTAL_SWITCHER_PAGES*PAGE_SIZE;

        /*
         * Now we reserve the "virtual memory area"s we want.  We might
         * not get them in theory, but in practice it's worked so far.
         *
         * We want the switcher text to be read-only and executable, and
         * the stacks to be read-write and non-executable.
         */
        switcher_text_vma = __get_vm_area(PAGE_SIZE, VM_ALLOC|VM_NO_GUARD,
                                          switcher_addr,
                                          switcher_addr + PAGE_SIZE);

        if (!switcher_text_vma) {
                err = -ENOMEM;
                printk("lguest: could not map switcher pages high\n");
                goto free_pages;
        }

        switcher_stacks_vma = __get_vm_area(SWITCHER_STACK_PAGES * PAGE_SIZE,
                                            VM_ALLOC|VM_NO_GUARD,
                                            switcher_addr + PAGE_SIZE,
                                            switcher_addr + TOTAL_SWITCHER_PAGES * PAGE_SIZE);
        if (!switcher_stacks_vma) {
                err = -ENOMEM;
                printk("lguest: could not map switcher pages high\n");
                goto free_text_vma;
        }

        /*
         * This code actually sets up the pages we've allocated to appear at
         * switcher_addr.  map_vm_area() takes the vma we allocated above, the
         * kind of pages we're mapping (kernel text pages and kernel writable
         * pages respectively), and a pointer to our array of struct pages.
         */
        err = map_vm_area(switcher_text_vma, PAGE_KERNEL_RX, lg_switcher_pages);
        if (err) {
                printk("lguest: text map_vm_area failed: %i\n", err);
                goto free_vmas;
        }

        err = map_vm_area(switcher_stacks_vma, PAGE_KERNEL,
                          lg_switcher_pages + SWITCHER_TEXT_PAGES);
        if (err) {
                printk("lguest: stacks map_vm_area failed: %i\n", err);
                goto free_vmas;
        }

        /*
         * Now the Switcher is mapped at the right address, we can't fail!
         */
        printk(KERN_INFO "lguest: mapped switcher at %p\n",
               switcher_text_vma->addr);
        /* And we succeeded... */
        return 0;

free_vmas:
        /* Undoes map_vm_area and __get_vm_area */
        vunmap(switcher_stacks_vma->addr);
free_text_vma:
        vunmap(switcher_text_vma->addr);
free_pages:
        i = TOTAL_SWITCHER_PAGES;
free_some_pages:
        for (--i; i >= 0; i--)
                __free_pages(lg_switcher_pages[i], 0);
        kfree(lg_switcher_pages);
out:
        return err;
}
/*:*/

/* Cleaning up the mapping when the module is unloaded is almost... too easy. */
static void unmap_switcher(void)
{
        unsigned int i;

        /* vunmap() undoes *both* map_vm_area() and __get_vm_area(). */
        vunmap(switcher_text_vma->addr);
        vunmap(switcher_stacks_vma->addr);
        /* Now we just need to free the pages we copied the switcher into */
        for (i = 0; i < TOTAL_SWITCHER_PAGES; i++)
                __free_pages(lg_switcher_pages[i], 0);
        kfree(lg_switcher_pages);
}

/*H:032
 * Dealing With Guest Memory.
 *
 * Before we go too much further into the Host, we need to grok the routines
 * we use to deal with Guest memory.
 *
 * When the Guest gives us (what it thinks is) a physical address, we can use
 * the normal copy_from_user() & copy_to_user() on the corresponding place in
 * the memory region allocated by the Launcher.
 *
 * But we can't trust the Guest: it might be trying to access the Launcher
 * code.  We have to check that the range is below the pfn_limit the Launcher
 * gave us.  We have to make sure that addr + len doesn't give us a false
 * positive by overflowing, too.
 */
bool lguest_address_ok(const struct lguest *lg,
                       unsigned long addr, unsigned long len)
{
        return addr+len <= lg->pfn_limit * PAGE_SIZE && (addr+len >= addr);
}

/*
 * This routine copies memory from the Guest.  Here we can see how useful the
 * kill_lguest() routine we met in the Launcher can be: we return a random
 * value (all zeroes) instead of needing to return an error.
 */
void __lgread(struct lg_cpu *cpu, void *b, unsigned long addr, unsigned bytes)
{
        if (!lguest_address_ok(cpu->lg, addr, bytes)
            || copy_from_user(b, cpu->lg->mem_base + addr, bytes) != 0) {
                /* copy_from_user should do this, but as we rely on it... */
                memset(b, 0, bytes);
                kill_guest(cpu, "bad read address %#lx len %u", addr, bytes);
        }
}

/* This is the write (copy into Guest) version. */
void __lgwrite(struct lg_cpu *cpu, unsigned long addr, const void *b,
               unsigned bytes)
{
        if (!lguest_address_ok(cpu->lg, addr, bytes)
            || copy_to_user(cpu->lg->mem_base + addr, b, bytes) != 0)
                kill_guest(cpu, "bad write address %#lx len %u", addr, bytes);
}
/*:*/

/*H:030
 * Let's jump straight to the the main loop which runs the Guest.
 * Remember, this is called by the Launcher reading /dev/lguest, and we keep
 * going around and around until something interesting happens.
 */
int run_guest(struct lg_cpu *cpu, unsigned long __user *user)
{
        /* If the launcher asked for a register with LHREQ_GETREG */
        if (cpu->reg_read) {
                if (put_user(*cpu->reg_read, user))
                        return -EFAULT;
                cpu->reg_read = NULL;
                return sizeof(*cpu->reg_read);
        }

        /* We stop running once the Guest is dead. */
        while (!cpu->lg->dead) {
                unsigned int irq;
                bool more;

                /* First we run any hypercalls the Guest wants done. */
                if (cpu->hcall)
                        do_hypercalls(cpu);

                /* Do we have to tell the Launcher about a trap? */
                if (cpu->pending.trap) {
                        if (copy_to_user(user, &cpu->pending,
                                         sizeof(cpu->pending)))
                                return -EFAULT;
                        return sizeof(cpu->pending);
                }

                /*
                 * All long-lived kernel loops need to check with this horrible
                 * thing called the freezer.  If the Host is trying to suspend,
                 * it stops us.
                 */
                try_to_freeze();

                /* Check for signals */
                if (signal_pending(current))
                        return -ERESTARTSYS;

                /*
                 * Check if there are any interrupts which can be delivered now:
                 * if so, this sets up the hander to be executed when we next
                 * run the Guest.
                 */
                irq = interrupt_pending(cpu, &more);
                if (irq < LGUEST_IRQS)
                        try_deliver_interrupt(cpu, irq, more);

                /*
                 * Just make absolutely sure the Guest is still alive.  One of
                 * those hypercalls could have been fatal, for example.
                 */
                if (cpu->lg->dead)
                        break;

                /*
                 * If the Guest asked to be stopped, we sleep.  The Guest's
                 * clock timer will wake us.
                 */
                if (cpu->halted) {
                        set_current_state(TASK_INTERRUPTIBLE);
                        /*
                         * Just before we sleep, make sure no interrupt snuck in
                         * which we should be doing.
                         */
                        if (interrupt_pending(cpu, &more) < LGUEST_IRQS)
                                set_current_state(TASK_RUNNING);
                        else
                                schedule();
                        continue;
                }

                /*
                 * OK, now we're ready to jump into the Guest.  First we put up
                 * the "Do Not Disturb" sign:
                 */
                local_irq_disable();

                /* Actually run the Guest until something happens. */
                lguest_arch_run_guest(cpu);

                /* Now we're ready to be interrupted or moved to other CPUs */
                local_irq_enable();

                /* Now we deal with whatever happened to the Guest. */
                lguest_arch_handle_trap(cpu);
        }

        /* Special case: Guest is 'dead' but wants a reboot. */
        if (cpu->lg->dead == ERR_PTR(-ERESTART))
                return -ERESTART;

        /* The Guest is dead => "No such file or directory" */
        return -ENOENT;
}

/*H:000
 * Welcome to the Host!
 *
 * By this point your brain has been tickled by the Guest code and numbed by
 * the Launcher code; prepare for it to be stretched by the Host code.  This is
 * the heart.  Let's begin at the initialization routine for the Host's lg
 * module.
 */
static int __init init(void)
{
        int err;

        /* Lguest can't run under Xen, VMI or itself.  It does Tricky Stuff. */
        if (get_kernel_rpl() != 0) {
                printk("lguest is afraid of being a guest\n");
                return -EPERM;
        }

        /* First we put the Switcher up in very high virtual memory. */
        err = map_switcher();
        if (err)
                goto out;

        /* We might need to reserve an interrupt vector. */
        err = init_interrupts();
        if (err)
                goto unmap;

        /* /dev/lguest needs to be registered. */
        err = lguest_device_init();
        if (err)
                goto free_interrupts;

        /* Finally we do some architecture-specific setup. */
        lguest_arch_host_init();

        /* All good! */
        return 0;

free_interrupts:
        free_interrupts();
unmap:
        unmap_switcher();
out:
        return err;
}

/* Cleaning up is just the same code, backwards.  With a little French. */
static void __exit fini(void)
{
        lguest_device_remove();
        free_interrupts();
        unmap_switcher();

        lguest_arch_host_fini();
}
/*:*/

/*
 * The Host side of lguest can be a module.  This is a nice way for people to
 * play with it.
 */
module_init(init);
module_exit(fini);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");