/*P:100 This is the Launcher code, a simple program which lays out the
- * "physical" memory for the new Guest by mapping the kernel image and the
- * virtual devices, then reads repeatedly from /dev/lguest to run the Guest.
-:*/
+ * "physical" memory for the new Guest by mapping the kernel image and
+ * the virtual devices, then opens /dev/lguest to tell the kernel
+ * about the Guest and control it. :*/
#define _LARGEFILE64_SOURCE
#define _GNU_SOURCE
#include <stdio.h>
#include "linux/virtio_console.h"
#include "linux/virtio_ring.h"
#include "asm-x86/bootparam.h"
-/*L:110 We can ignore the 38 include files we need for this program, but I do
+/*L:110 We can ignore the 39 include files we need for this program, but I do
* want to draw attention to the use of kernel-style types.
*
* As Linus said, "C is a Spartan language, and so should your naming be." I
err(1, "Reading program headers");
/* Try all the headers: there are usually only three. A read-only one,
- * a read-write one, and a "note" section which isn't loadable. */
+ * a read-write one, and a "note" section which we don't load. */
for (i = 0; i < ehdr->e_phnum; i++) {
/* If this isn't a loadable segment, we ignore it */
if (phdr[i].p_type != PT_LOAD)
if (memcmp(hdr.e_ident, ELFMAG, SELFMAG) == 0)
return map_elf(fd, &hdr);
- /* Otherwise we assume it's a bzImage, and try to unpack it */
+ /* Otherwise we assume it's a bzImage, and try to load it. */
return load_bzimage(fd);
}
return len;
}
-/* Once we know how much memory we have, we can construct simple linear page
+/* Once we know how much memory we have we can construct simple linear page
* tables which set virtual == physical which will get the Guest far enough
* into the boot to create its own.
*
* We lay them out of the way, just below the initrd (which is why we need to
- * know its size). */
+ * know its size here). */
static unsigned long setup_pagetables(unsigned long mem,
unsigned long initrd_size)
{
*
* Handling output for network is also simple: we get all the output buffers
* and write them (ignoring the first element) to this device's file descriptor
- * (stdout). */
+ * (/dev/net/tun).
+ */
static void handle_net_output(int fd, struct virtqueue *vq)
{
unsigned int head, out, in;
write(waker_fd, &vq->dev->fd, sizeof(vq->dev->fd));
}
-/* Resetting a device is fairly easy. */
+/* When the Guest asks us to reset a device, it's is fairly easy. */
static void reset_device(struct device *dev)
{
struct virtqueue *vq;
if (select(devices.max_infd+1, &fds, NULL, NULL, &poll) == 0)
break;
- /* Otherwise, call the device(s) which have readable
- * file descriptors and a method of handling them. */
+ /* Otherwise, call the device(s) which have readable file
+ * descriptors and a method of handling them. */
for (i = devices.dev; i; i = i->next) {
if (i->handle_input && FD_ISSET(i->fd, &fds)) {
int dev_fd;
* should no longer service it. Networking and
* console do this when there's no input
* buffers to deliver into. Console also uses
- * it when it discovers that stdin is
- * closed. */
+ * it when it discovers that stdin is closed. */
FD_CLR(i->fd, &devices.infds);
/* Tell waker to ignore it too, by sending a
* negative fd number (-1, since 0 is a valid
*
* All devices need a descriptor so the Guest knows it exists, and a "struct
* device" so the Launcher can keep track of it. We have common helper
- * routines to allocate and manage them. */
+ * routines to allocate and manage them.
+ */
/* The layout of the device page is a "struct lguest_device_desc" followed by a
* number of virtqueue descriptors, then two sets of feature bits, then an
struct virtqueue **i, *vq = malloc(sizeof(*vq));
void *p;
- /* First we need some pages for this virtqueue. */
+ /* First we need some memory for this virtqueue. */
pages = (vring_size(num_descs, getpagesize()) + getpagesize() - 1)
/ getpagesize();
p = get_pages(pages);
}
/* The first half of the feature bitmask is for us to advertise features. The
- * second half if for the Guest to accept features. */
+ * second half is for the Guest to accept features. */
static void add_feature(struct device *dev, unsigned bit)
{
u8 *features = get_feature_bits(dev);
}
/* This routine does all the creation and setup of a new device, including
- * calling new_dev_desc() to allocate the descriptor and device memory. */
+ * calling new_dev_desc() to allocate the descriptor and device memory.
+ *
+ * See what I mean about userspace being boring? */
static struct device *new_device(const char *name, u16 type, int fd,
bool (*handle_input)(int, struct device *))
{
while (read(vblk->workpipe[0], &c, 1) == 1) {
/* We acknowledge each request immediately to reduce latency,
* rather than waiting until we've done them all. I haven't
- * measured to see if it makes any difference. */
+ * measured to see if it makes any difference.
+ *
+ * That would be an interesting test, wouldn't it? You could
+ * also try having more than one I/O thread. */
while (service_io(dev))
write(vblk->done_fd, &c, 1);
}
}
/* Now we've seen the I/O thread, we return to the Launcher to see what happens
- * when the thread tells us it's completed some I/O. */
+ * when that thread tells us it's completed some I/O. */
static bool handle_io_finish(int fd, struct device *dev)
{
char c;
* more work. */
pipe(vblk->workpipe);
- /* Create stack for thread and run it */
+ /* Create stack for thread and run it. Since stack grows upwards, we
+ * point the stack pointer to the end of this region. */
stack = malloc(32768);
/* SIGCHLD - We dont "wait" for our cloned thread, so prevent it from
* becoming a zombie. */
- if (clone(io_thread, stack + 32768, CLONE_VM | SIGCHLD, dev) == -1)
+ if (clone(io_thread, stack + 32768, CLONE_VM | SIGCHLD, dev) == -1)
err(1, "Creating clone");
/* We don't need to keep the I/O thread's end of the pipes open. */
verbose("device %u: virtblock %llu sectors\n",
devices.device_num, le64_to_cpu(conf.capacity));
}
-/* That's the end of device setup. :*/
+/* That's the end of device setup. */
-/* Reboot */
+/*L:230 Reboot is pretty easy: clean up and exec() the Launcher afresh. */
static void __attribute__((noreturn)) restart_guest(void)
{
unsigned int i;
- /* Closing pipes causes the waker thread and io_threads to die, and
+ /* Closing pipes causes the Waker thread and io_threads to die, and
* closing /dev/lguest cleans up the Guest. Since we don't track all
* open fds, we simply close everything beyond stderr. */
for (i = 3; i < FD_SETSIZE; i++)
err(1, "Could not exec %s", main_args[0]);
}
-/*L:220 Finally we reach the core of the Launcher, which runs the Guest, serves
+/*L:220 Finally we reach the core of the Launcher which runs the Guest, serves
* its input and output, and finally, lays it to rest. */
static void __attribute__((noreturn)) run_guest(int lguest_fd)
{
err(1, "Resetting break");
}
}
-/*
+/*L:240
* This is the end of the Launcher. The good news: we are over halfway
* through! The bad news: the most fiendish part of the code still lies ahead
* of us.
* device receive input from a file descriptor, we keep an fdset
* (infds) and the maximum fd number (max_infd) with the head of the
* list. We also keep a pointer to the last device. Finally, we keep
- * the next interrupt number to hand out (1: remember that 0 is used by
- * the timer). */
+ * the next interrupt number to use for devices (1: remember that 0 is
+ * used by the timer). */
FD_ZERO(&devices.infds);
devices.max_infd = -1;
devices.lastdev = NULL;
lguest_fd = tell_kernel(pgdir, start);
/* We fork off a child process, which wakes the Launcher whenever one
- * of the input file descriptors needs attention. Otherwise we would
- * run the Guest until it tries to output something. */
+ * of the input file descriptors needs attention. We call this the
+ * Waker, and we'll cover it in a moment. */
waker_fd = setup_waker(lguest_fd);
/* Finally, run the Guest. This doesn't return. */
* (such as the example in Documentation/lguest/lguest.c) is called the
* Launcher.
*
- * Secondly, we only run specially modified Guests, not normal kernels. When
- * you set CONFIG_LGUEST to 'y' or 'm', this automatically sets
- * CONFIG_LGUEST_GUEST=y, which compiles this file into the kernel so it knows
- * how to be a Guest. This means that you can use the same kernel you boot
- * normally (ie. as a Host) as a Guest.
+ * Secondly, we only run specially modified Guests, not normal kernels: setting
+ * CONFIG_LGUEST_GUEST to "y" compiles this file into the kernel so it knows
+ * how to be a Guest at boot time. This means that you can use the same kernel
+ * you boot normally (ie. as a Host) as a Guest.
*
* These Guests know that they cannot do privileged operations, such as disable
* interrupts, and that they have to ask the Host to do such things explicitly.
* This file consists of all the replacements for such low-level native
* hardware operations: these special Guest versions call the Host.
*
- * So how does the kernel know it's a Guest? The Guest starts at a special
- * entry point marked with a magic string, which sets up a few things then
- * calls here. We replace the native functions various "paravirt" structures
- * with our Guest versions, then boot like normal. :*/
+ * So how does the kernel know it's a Guest? We'll see that later, but let's
+ * just say that we end up here where we replace the native functions various
+ * "paravirt" structures with our Guest versions, then boot like normal. :*/
/*
* Copyright (C) 2006, Rusty Russell <rusty@rustcorp.com.au> IBM Corporation.
* lguest_leave_lazy_mode().
*
* So, when we're in lazy mode, we call async_hcall() to store the call for
- * future processing. */
+ * future processing: */
static void lazy_hcall(unsigned long call,
unsigned long arg1,
unsigned long arg2,
}
/* When lazy mode is turned off reset the per-cpu lazy mode variable and then
- * issue a hypercall to flush any stored calls. */
+ * issue the do-nothing hypercall to flush any stored calls. */
static void lguest_leave_lazy_mode(void)
{
paravirt_leave_lazy(paravirt_get_lazy_mode());
*
* So instead we keep an "irq_enabled" field inside our "struct lguest_data",
* which the Guest can update with a single instruction. The Host knows to
- * check there when it wants to deliver an interrupt.
+ * check there before it tries to deliver an interrupt.
*/
/* save_flags() is expected to return the processor state (ie. "flags"). The
/*M:003 Note that we don't check for outstanding interrupts when we re-enable
* them (or when we unmask an interrupt). This seems to work for the moment,
* since interrupts are rare and we'll just get the interrupt on the next timer
- * tick, but when we turn on CONFIG_NO_HZ, we should revisit this. One way
+ * tick, but now we can run with CONFIG_NO_HZ, we should revisit this. One way
* would be to put the "irq_enabled" field in a page by itself, and have the
* Host write-protect it when an interrupt comes in when irqs are disabled.
- * There will then be a page fault as soon as interrupts are re-enabled. :*/
+ * There will then be a page fault as soon as interrupts are re-enabled.
+ *
+ * A better method is to implement soft interrupt disable generally for x86:
+ * instead of disabling interrupts, we set a flag. If an interrupt does come
+ * in, we then disable them for real. This is uncommon, so we could simply use
+ * a hypercall for interrupt control and not worry about efficiency. :*/
/*G:034
* The Interrupt Descriptor Table (IDT).
static void lguest_write_idt_entry(gate_desc *dt,
int entrynum, const gate_desc *g)
{
+ /* The gate_desc structure is 8 bytes long: we hand it to the Host in
+ * two 32-bit chunks. The whole 32-bit kernel used to hand descriptors
+ * around like this; typesafety wasn't a big concern in Linux's early
+ * years. */
u32 *desc = (u32 *)g;
/* Keep the local copy up to date. */
native_write_idt_entry(dt, entrynum, g);
*
* This is the opposite of the IDT code where we have a LOAD_IDT_ENTRY
* hypercall and use that repeatedly to load a new IDT. I don't think it
- * really matters, but wouldn't it be nice if they were the same?
+ * really matters, but wouldn't it be nice if they were the same? Wouldn't
+ * it be even better if you were the one to send the patch to fix it?
*/
static void lguest_load_gdt(const struct desc_ptr *desc)
{
/* The "cpuid" instruction is a way of querying both the CPU identity
* (manufacturer, model, etc) and its features. It was introduced before the
- * Pentium in 1993 and keeps getting extended by both Intel and AMD. As you
- * might imagine, after a decade and a half this treatment, it is now a giant
- * ball of hair. Its entry in the current Intel manual runs to 28 pages.
+ * Pentium in 1993 and keeps getting extended by both Intel, AMD and others.
+ * As you might imagine, after a decade and a half this treatment, it is now a
+ * giant ball of hair. Its entry in the current Intel manual runs to 28 pages.
*
* This instruction even it has its own Wikipedia entry. The Wikipedia entry
* has been translated into 4 languages. I am not making this up!
return lguest_data.time.tv_sec;
}
-/* The TSC is a Time Stamp Counter. The Host tells us what speed it runs at,
- * or 0 if it's unusable as a reliable clock source. This matches what we want
- * here: if we return 0 from this function, the x86 TSC clock will not register
- * itself. */
+/* The TSC is an Intel thing called the Time Stamp Counter. The Host tells us
+ * what speed it runs at, or 0 if it's unusable as a reliable clock source.
+ * This matches what we want here: if we return 0 from this function, the x86
+ * TSC clock will give up and not register itself. */
static unsigned long lguest_cpu_khz(void)
{
return lguest_data.tsc_khz;
}
-/* If we can't use the TSC, the kernel falls back to our "lguest_clock", where
- * we read the time value given to us by the Host. */
+/* If we can't use the TSC, the kernel falls back to our lower-priority
+ * "lguest_clock", where we read the time value given to us by the Host. */
static cycle_t lguest_clock_read(void)
{
unsigned long sec, nsec;
static int lguest_clockevent_set_next_event(unsigned long delta,
struct clock_event_device *evt)
{
+ /* FIXME: I don't think this can ever happen, but James tells me he had
+ * to put this code in. Maybe we should remove it now. Anyone? */
if (delta < LG_CLOCK_MIN_DELTA) {
if (printk_ratelimit())
printk(KERN_DEBUG "%s: small delta %lu ns\n",
__FUNCTION__, delta);
return -ETIME;
}
+
+ /* Please wake us this far in the future. */
hcall(LHCALL_SET_CLOCKEVENT, delta, 0, 0);
return 0;
}
* will not tolerate us trying to use that), the stack pointer, and the number
* of pages in the stack. */
static void lguest_load_sp0(struct tss_struct *tss,
- struct thread_struct *thread)
+ struct thread_struct *thread)
{
lazy_hcall(LHCALL_SET_STACK, __KERNEL_DS|0x1, thread->sp0,
THREAD_SIZE/PAGE_SIZE);
hcall(LHCALL_HALT, 0, 0, 0);
}
-/* Perhaps CRASH isn't the best name for this hypercall, but we use it to get a
- * message out when we're crashing as well as elegant termination like powering
- * off.
+/* The SHUTDOWN hypercall takes a string to describe what's happening, and
+ * an argument which says whether this to restart (reboot) the Guest or not.
*
* Note that the Host always prefers that the Guest speak in physical addresses
* rather than virtual addresses, so we use __pa() here. */
/* Setting up memory is fairly easy. */
static __init char *lguest_memory_setup(void)
{
- /* We do this here and not earlier because lockcheck barfs if we do it
- * before start_kernel() */
+ /* We do this here and not earlier because lockcheck used to barf if we
+ * did it before start_kernel(). I think we fixed that, so it'd be
+ * nice to move it back to lguest_init. Patch welcome... */
atomic_notifier_chain_register(&panic_notifier_list, &paniced);
/* The Linux bootloader header contains an "e820" memory map: the
return len;
}
+/* Rebooting also tells the Host we're finished, but the RESTART flag tells the
+ * Launcher to reboot us. */
+static void lguest_restart(char *reason)
+{
+ hcall(LHCALL_SHUTDOWN, __pa(reason), LGUEST_SHUTDOWN_RESTART, 0);
+}
+
/*G:050
* Patching (Powerfully Placating Performance Pedants)
*
- * We have already seen that pv_ops structures let us replace simple
- * native instructions with calls to the appropriate back end all throughout
- * the kernel. This allows the same kernel to run as a Guest and as a native
+ * We have already seen that pv_ops structures let us replace simple native
+ * instructions with calls to the appropriate back end all throughout the
+ * kernel. This allows the same kernel to run as a Guest and as a native
* kernel, but it's slow because of all the indirect branches.
*
* Remember that David Wheeler quote about "Any problem in computer science can
return insn_len;
}
-static void lguest_restart(char *reason)
-{
- hcall(LHCALL_SHUTDOWN, __pa(reason), LGUEST_SHUTDOWN_RESTART, 0);
-}
-
-/*G:030 Once we get to lguest_init(), we know we're a Guest. The pv_ops
- * structures in the kernel provide points for (almost) every routine we have
- * to override to avoid privileged instructions. */
+/*G:030 Once we get to lguest_init(), we know we're a Guest. The various
+ * pv_ops structures in the kernel provide points for (almost) every routine we
+ * have to override to avoid privileged instructions. */
__init void lguest_init(void)
{
/* We're under lguest, paravirt is enabled, and we're running at
* the normal data segment to get through booting. */
asm volatile ("mov %0, %%fs" : : "r" (__KERNEL_DS) : "memory");
- /* The Host uses the top of the Guest's virtual address space for the
- * Host<->Guest Switcher, and it tells us how big that is in
- * lguest_data.reserve_mem, set up on the LGUEST_INIT hypercall. */
+ /* The Host<->Guest Switcher lives at the top of our address space, and
+ * the Host told us how big it is when we made LGUEST_INIT hypercall:
+ * it put the answer in lguest_data.reserve_mem */
reserve_top_address(lguest_data.reserve_mem);
/* If we don't initialize the lock dependency checker now, it crashes
/* Math is always hard! */
new_cpu_data.hard_math = 1;
+ /* We don't have features. We have puppies! Puppies! */
#ifdef CONFIG_X86_MCE
mce_disabled = 1;
#endif
virtio_cons_early_init(early_put_chars);
/* Last of all, we set the power management poweroff hook to point to
- * the Guest routine to power off. */
+ * the Guest routine to power off, and the reboot hook to our restart
+ * routine. */
pm_power_off = lguest_power_off;
-
machine_ops.restart = lguest_restart;
+
/* Now we're set up, call start_kernel() in init/main.c and we proceed
* to boot as normal. It never returns. */
start_kernel();
#include <asm/thread_info.h>
#include <asm/processor-flags.h>
-/*G:020 This is where we begin: head.S notes that the boot header's platform
- * type field is "1" (lguest), so calls us here.
+/*G:020 Our story starts with the kernel booting into startup_32 in
+ * arch/x86/kernel/head_32.S. It expects a boot header, which is created by
+ * the bootloader (the Launcher in our case).
+ *
+ * The startup_32 function does very little: it clears the uninitialized global
+ * C variables which we expect to be zero (ie. BSS) and then copies the boot
+ * header and kernel command line somewhere safe. Finally it checks the
+ * 'hardware_subarch' field. This was introduced in 2.6.24 for lguest and Xen:
+ * if it's set to '1' (lguest's assigned number), then it calls us here.
*
* WARNING: be very careful here! We're running at addresses equal to physical
* addesses (around 0), not above PAGE_OFFSET as most code expectes
* (eg. 0xC0000000). Jumps are relative, so they're OK, but we can't touch any
- * data.
+ * data without remembering to subtract __PAGE_OFFSET!
*
* The .section line puts this code in .init.text so it will be discarded after
* boot. */
int $LGUEST_TRAP_ENTRY
/* The Host put the toplevel pagetable in lguest_data.pgdir. The movsl
- * instruction uses %esi implicitly as the source for the copy we'
+ * instruction uses %esi implicitly as the source for the copy we're
* about to do. */
movl lguest_data - __PAGE_OFFSET + LGUEST_DATA_pgdir, %esi
/*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, and a
- * couple of non-obvious setup and teardown pieces which were implemented after
- * days of debugging pain. :*/
+ * Host to do something. This file also contains useful helper routines. :*/
#include <linux/module.h>
#include <linux/stringify.h>
#include <linux/stddef.h>
* easy.
*/
- /* We allocate an array of "struct page"s. map_vm_area() wants the
- * pages in this form, rather than just an array of pointers. */
+ /* We allocate an array of struct page pointers. map_vm_area() wants
+ * this, rather than just an array of pages. */
switcher_page = kmalloc(sizeof(switcher_page[0])*TOTAL_SWITCHER_PAGES,
GFP_KERNEL);
if (!switcher_page) {
}
}
-/* This is the write (copy into guest) version. */
+/* This is the write (copy into Guest) version. */
void __lgwrite(struct lg_cpu *cpu, unsigned long addr, const void *b,
unsigned bytes)
{
if (cpu->break_out)
return -EAGAIN;
- /* 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. */
+ /* 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. */
maybe_do_interrupt(cpu);
/* All long-lived kernel loops need to check with this horrible
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;
}
#include "lg.h"
/*H:120 This is the core hypercall routine: where the Guest gets what it wants.
- * Or gets killed. Or, in the case of LHCALL_CRASH, both. */
+ * Or gets killed. Or, in the case of LHCALL_SHUTDOWN, both. */
static void do_hcall(struct lg_cpu *cpu, struct hcall_args *args)
{
switch (args->arg0) {
* pagetable. */
guest_pagetable_clear_all(cpu);
}
+/*:*/
+
+/*M:013 If a Guest reads from a page (so creates a mapping) that it has never
+ * written to, and then the Launcher writes to it (ie. the output of a virtual
+ * device), the Guest will still see the old page. In practice, this never
+ * happens: why would the Guest read a page which it has never written to? But
+ * a similar scenario might one day bite us, so it's worth mentioning. :*/
/*H:100
* Hypercalls
* However, if we are signalled or the Guest sends I/O to the
* Launcher, the run_guest() loop will exit without running the
* Guest. When it comes back it would try to re-run the
- * hypercall. */
+ * hypercall. Finding that bug sucked. */
cpu->hcall = NULL;
}
}
if (copy_from_user(&blk, cpu->lg->lguest_data->blocked_interrupts,
sizeof(blk)))
return;
-
bitmap_andnot(blk, cpu->irqs_pending, blk, LGUEST_IRQS);
/* Find the first interrupt. */
clear_bit(syscall_vector, used_vectors);
}
-/*H:220 Now we've got the routines to deliver interrupts, delivering traps
- * like page fault is easy. The only trick is that Intel decided that some
- * traps should have error codes: */
+/*H:220 Now we've got the routines to deliver interrupts, delivering traps like
+ * page fault is easy. The only trick is that Intel decided that some traps
+ * should have error codes: */
static int has_err(unsigned int trap)
{
return (trap == 8 || (trap >= 10 && trap <= 14) || trap == 17);
/*P:050 Lguest guests use a very simple method to describe devices. It's a
- * series of device descriptors contained just above the top of normal
+ * series of device descriptors contained just above the top of normal Guest
* memory.
*
* We use the standard "virtio" device infrastructure, which provides us with a
* console, a network and a block driver. Each one expects some configuration
- * information and a "virtqueue" mechanism to send and receive data. :*/
+ * information and a "virtqueue" or two to send and receive data. :*/
#include <linux/init.h>
#include <linux/bootmem.h>
#include <linux/lguest_launcher.h>
* Device configurations
*
* The configuration information for a device consists of one or more
- * virtqueues, a feature bitmaks, and some configuration bytes. The
+ * virtqueues, a feature bitmap, and some configuration bytes. The
* configuration bytes don't really matter to us: the Launcher sets them up, and
* the driver will look at them during setup.
*
};
/* When the virtio_ring code wants to prod the Host, it calls us here and we
- * make a hypercall. We hand the page number of the virtqueue so the Host
+ * make a hypercall. We hand the physical address of the virtqueue so the Host
* knows which virtqueue we're talking about. */
static void lg_notify(struct virtqueue *vq)
{
* allocate its own pages and tell the Host where they are, but for lguest it's
* simpler for the Host to simply tell us where the pages are.
*
- * So we provide devices with a "find virtqueue and set it up" function. */
+ * So we provide drivers with a "find the Nth virtqueue and set it up"
+ * function. */
static struct virtqueue *lg_find_vq(struct virtio_device *vdev,
unsigned index,
void (*callback)(struct virtqueue *vq))
if (current != cpu->tsk)
return -EPERM;
- /* If the guest is already dead, we indicate why */
+ /* If the Guest is already dead, we indicate why */
if (lg->dead) {
size_t len;
return len;
}
- /* If we returned from read() last time because the Guest notified,
+ /* If we returned from read() last time because the Guest sent I/O,
* clear the flag. */
if (cpu->pending_notify)
cpu->pending_notify = 0;
return run_guest(cpu, (unsigned long __user *)user);
}
+/*L:025 This actually initializes a CPU. For the moment, a Guest is only
+ * uniprocessor, so "id" is always 0. */
static int lg_cpu_start(struct lg_cpu *cpu, unsigned id, unsigned long start_ip)
{
+ /* We have a limited number the number of CPUs in the lguest struct. */
if (id >= NR_CPUS)
return -EINVAL;
+ /* Set up this CPU's id, and pointer back to the lguest struct. */
cpu->id = id;
cpu->lg = container_of((cpu - id), struct lguest, cpus[0]);
cpu->lg->nr_cpus++;
+
+ /* Each CPU has a timer it can set. */
init_clockdev(cpu);
/* We need a complete page for the Guest registers: they are accessible
* address. */
lguest_arch_setup_regs(cpu, start_ip);
- /* Initialize the queue for the waker to wait on */
+ /* Initialize the queue for the Waker to wait on */
init_waitqueue_head(&cpu->break_wq);
/* We keep a pointer to the Launcher task (ie. current task) for when
- * other Guests want to wake this one (inter-Guest I/O). */
+ * other Guests want to wake this one (eg. console input). */
cpu->tsk = current;
/* We need to keep a pointer to the Launcher's memory map, because if
* when the same Guest runs on the same CPU twice. */
cpu->last_pages = NULL;
+ /* No error == success. */
return 0;
}
lg->mem_base = (void __user *)(long)args[0];
lg->pfn_limit = args[1];
- /* This is the first cpu */
+ /* This is the first cpu (cpu 0) and it will start booting at args[3] */
err = lg_cpu_start(&lg->cpus[0], 0, args[3]);
if (err)
goto release_guest;
/* Initialize the Guest's shadow page tables, using the toplevel
- * address the Launcher gave us. This allocates memory, so can
- * fail. */
+ * address the Launcher gave us. This allocates memory, so can fail. */
err = init_guest_pagetable(lg, args[2]);
if (err)
goto free_regs;
/*L:010 The first operation the Launcher does must be a write. All writes
* start with an unsigned long number: for the first write this must be
* LHREQ_INITIALIZE to set up the Guest. After that the Launcher can use
- * writes of other values to send interrupts. */
+ * writes of other values to send interrupts.
+ *
+ * Note that we overload the "offset" in the /dev/lguest file to indicate what
+ * CPU number we're dealing with. Currently this is always 0, since we only
+ * support uniprocessor Guests, but you can see the beginnings of SMP support
+ * here. */
static ssize_t write(struct file *file, const char __user *in,
size_t size, loff_t *off)
{
- /* Once the guest is initialized, we hold the "struct lguest" in the
+ /* Once the Guest is initialized, we hold the "struct lguest" in the
* file private data. */
struct lguest *lg = file->private_data;
const unsigned long __user *input = (const unsigned long __user *)in;
struct lg_cpu *uninitialized_var(cpu);
unsigned int cpu_id = *off;
+ /* The first value tells us what this request is. */
if (get_user(req, input) != 0)
return -EFAULT;
input++;
* previous encounters. It's functional, and as neat as it can be in the
* circumstances, but be wary, for these things are subtle and break easily.
* The Guest provides a virtual to physical mapping, but we can neither trust
- * it nor use it: we verify and convert it here to point the hardware to the
- * actual Guest pages when running the Guest. :*/
+ * it nor use it: we verify and convert it here then point the CPU to the
+ * converted Guest pages when running the Guest. :*/
/* Copyright (C) Rusty Russell IBM Corporation 2006.
* GPL v2 and any later version */
BUG_ON(!(pgd_flags(gpgd) & _PAGE_PRESENT));
return gpage + ((vaddr>>PAGE_SHIFT) % PTRS_PER_PTE) * sizeof(pte_t);
}
+/*:*/
+
+/*M:014 get_pfn is slow; it takes the mmap sem and calls get_user_pages. We
+ * could probably try to grab batches of pages here as an optimization
+ * (ie. pre-faulting). :*/
/*H:350 This routine takes a page number given by the Guest and converts it to
* an actual, physical page number. It can fail for several reasons: the
* and the page is read-only, or the write flag was set and the page was
* shared so had to be copied, but we ran out of memory.
*
- * This holds a reference to the page, so release_pte() is careful to
- * put that back. */
+ * This holds a reference to the page, so release_pte() is careful to put that
+ * back. */
static unsigned long get_pfn(unsigned long virtpfn, int write)
{
struct page *page;
* all processes. So when the page table above that address changes, we update
* all the page tables, not just the current one. This is rare.
*
- * The benefit is that when we have to track a new page table, we can copy keep
- * all the kernel mappings. This speeds up context switch immensely. */
+ * The benefit is that when we have to track a new page table, we can keep all
+ * the kernel mappings. This speeds up context switch immensely. */
void guest_set_pte(struct lg_cpu *cpu,
unsigned long gpgdir, unsigned long vaddr, pte_t gpte)
{
- /* Kernel mappings must be changed on all top levels. Slow, but
- * doesn't happen often. */
+ /* Kernel mappings must be changed on all top levels. Slow, but doesn't
+ * happen often. */
if (vaddr >= cpu->lg->kernel_address) {
unsigned int i;
for (i = 0; i < ARRAY_SIZE(cpu->lg->pgdirs); i++)
/* We've made it through the page table code. Perhaps our tired brains are
* still processing the details, or perhaps we're simply glad it's over.
*
- * If nothing else, note that all this complexity in juggling shadow page
- * tables in sync with the Guest's page tables is for one reason: for most
- * Guests this page table dance determines how bad performance will be. This
- * is why Xen uses exotic direct Guest pagetable manipulation, and why both
- * Intel and AMD have implemented shadow page table support directly into
- * hardware.
+ * If nothing else, note that all this complexity in juggling shadow page tables
+ * in sync with the Guest's page tables is for one reason: for most Guests this
+ * page table dance determines how bad performance will be. This is why Xen
+ * uses exotic direct Guest pagetable manipulation, and why both Intel and AMD
+ * have implemented shadow page table support directly into hardware.
*
* There is just one file remaining in the Host. */
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
+/*P:450 This file contains the x86-specific lguest code. It used to be all
+ * mixed in with drivers/lguest/core.c but several foolhardy code slashers
+ * wrestled most of the dependencies out to here in preparation for porting
+ * lguest to other architectures (see what I mean by foolhardy?).
+ *
+ * This also contains a couple of non-obvious setup and teardown pieces which
+ * were implemented after days of debugging pain. :*/
#include <linux/kernel.h>
#include <linux/start_kernel.h>
#include <linux/string.h>
* also simplify copy_in_guest_info(). Note that we'd still need to restore
* things when we exit to Launcher userspace, but that's fairly easy.
*
+ * We could also try using this hooks for PGE, but that might be too expensive.
+ *
* The hooks were designed for KVM, but we can also put them to good use. :*/
/*H:040 This is the i386-specific code to setup and run the Guest. Interrupts
* was doing. */
run_guest_once(cpu, lguest_pages(raw_smp_processor_id()));
- /* Note that the "regs" pointer contains two extra entries which are
+ /* Note that the "regs" structure contains two extra entries which are
* not really registers: a trap number which says what interrupt or
* trap made the switcher code come back, and an error code which some
* traps set. */
break;
case 14: /* We've intercepted a Page Fault. */
/* The Guest accessed a virtual address that wasn't mapped.
- * This happens a lot: we don't actually set up most of the
- * page tables for the Guest at all when we start: as it runs
- * it asks for more and more, and we set them up as
- * required. In this case, we don't even tell the Guest that
- * the fault happened.
+ * This happens a lot: we don't actually set up most of the page
+ * tables for the Guest at all when we start: as it runs it asks
+ * for more and more, and we set them up as required. In this
+ * case, we don't even tell the Guest that the fault happened.
*
* The errcode tells whether this was a read or a write, and
* whether kernel or userspace code. */
if (!deliver_trap(cpu, cpu->regs->trapnum))
/* If the Guest doesn't have a handler (either it hasn't
* registered any yet, or it's one of the faults we don't let
- * it handle), it dies with a cryptic error message. */
+ * it handle), it dies with this cryptic error message. */
kill_guest(cpu, "unhandled trap %li at %#lx (%#lx)",
cpu->regs->trapnum, cpu->regs->eip,
cpu->regs->trapnum == 14 ? cpu->arch.last_pagefault
* The only exception is the interrupt handlers in switcher.S: their
* addresses are placed in a table (default_idt_entries), so we need to
* update the table with the new addresses. switcher_offset() is a
- * convenience function which returns the distance between the builtin
- * switcher code and the high-mapped copy we just made. */
+ * convenience function which returns the distance between the
+ * compiled-in switcher code and the high-mapped copy we just made. */
for (i = 0; i < IDT_ENTRIES; i++)
default_idt_entries[i] += switcher_offset();
state->guest_gdt_desc.address = (long)&state->guest_gdt;
/* We know where we want the stack to be when the Guest enters
- * the switcher: in pages->regs. The stack grows upwards, so
+ * the Switcher: in pages->regs. The stack grows upwards, so
* we start it at the end of that structure. */
state->guest_tss.sp0 = (long)(&pages->regs + 1);
/* And this is the GDT entry to use for the stack: we keep a
{
u32 tsc_speed;
- /* The pointer to the Guest's "struct lguest_data" is the only
- * argument. We check that address now. */
+ /* The pointer to the Guest's "struct lguest_data" is the only argument.
+ * We check that address now. */
if (!lguest_address_ok(cpu->lg, cpu->hcall->arg1,
sizeof(*cpu->lg->lguest_data)))
return -EFAULT;
return 0;
}
+/*:*/
/*L:030 lguest_arch_setup_regs()
*
-/*P:900 This is the Switcher: code which sits at 0xFFC00000 to do the low-level
- * Guest<->Host switch. It is as simple as it can be made, but it's naturally
- * very specific to x86.
+/*P:900 This is the Switcher: code which sits at 0xFFC00000 astride both the
+ * Host and Guest to do the low-level Guest<->Host switch. It is as simple as
+ * it can be made, but it's naturally very specific to x86.
*
* You have now completed Preparation. If this has whet your appetite; if you
* are feeling invigorated and refreshed then the next, more challenging stage
// Interrupts are turned back on: we are Guest.
iret
-// We treat two paths to switch back to the Host
+// We tread two paths to switch back to the Host
// Yet both must save Guest state and restore Host
// So we put the routine in a macro.
#define SWITCH_TO_HOST \
#ifndef __ASSEMBLY__
#include <asm/hw_irq.h>
-/*G:031 First, how does our Guest contact the Host to ask for privileged
+/*G:031 But first, how does our Guest contact the Host to ask for privileged
* operations? There are two ways: the direct way is to make a "hypercall",
* to make requests of the Host Itself.
*
* a new device, we simply need to write a new virtio driver and create support
* for it in the Launcher: this code won't need to change.
*
+ * Virtio devices are also used by kvm, so we can simply reuse their optimized
+ * device drivers. And one day when everyone uses virtio, my plan will be
+ * complete. Bwahahahah!
+ *
* Devices are described by a simplified ID, a status byte, and some "config"
* bytes which describe this device's configuration. This is placed by the
* Launcher just above the top of physical memory:
/* The number of virtqueues (first in config array) */
__u8 num_vq;
/* The number of bytes of feature bits. Multiply by 2: one for host
- * features and one for guest acknowledgements. */
+ * features and one for Guest acknowledgements. */
__u8 feature_len;
/* The number of bytes of the config array after virtqueues. */
__u8 config_len;
git://ftp.safe.ca / safe / jmp / linux-2.6 / commitdiff