Commit e1e72965 authored by Rusty Russell's avatar Rusty Russell
Browse files

lguest: documentation update



Went through the documentation doing typo and content fixes.  This
patch contains only comment and whitespace changes.
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
parent 568a17ff
......@@ -360,8 +360,8 @@ static unsigned long load_bzimage(int fd)
}
/*L:140 Loading the kernel is easy when it's a "vmlinux", but most kernels
* come wrapped up in the self-decompressing "bzImage" format. With some funky
* coding, we can load those, too. */
* come wrapped up in the self-decompressing "bzImage" format. With a little
* work, we can load those, too. */
static unsigned long load_kernel(int fd)
{
Elf32_Ehdr hdr;
......@@ -464,6 +464,7 @@ static unsigned long setup_pagetables(unsigned long mem,
* to know where it is. */
return to_guest_phys(pgdir);
}
/*:*/
/* Simple routine to roll all the commandline arguments together with spaces
* between them. */
......@@ -480,9 +481,9 @@ static void concat(char *dst, char *args[])
dst[len] = '\0';
}
/* This is where we actually tell the kernel to initialize the Guest. We saw
* the arguments it expects when we looked at initialize() in lguest_user.c:
* the base of guest "physical" memory, the top physical page to allow, the
/*L:185 This is where we actually tell the kernel to initialize the Guest. We
* saw the arguments it expects when we looked at initialize() in lguest_user.c:
* the base of Guest "physical" memory, the top physical page to allow, the
* top level pagetable and the entry point for the Guest. */
static int tell_kernel(unsigned long pgdir, unsigned long start)
{
......@@ -512,13 +513,14 @@ static void add_device_fd(int fd)
/*L:200
* The Waker.
*
* With a console and network devices, we can have lots of input which we need
* to process. We could try to tell the kernel what file descriptors to watch,
* but handing a file descriptor mask through to the kernel is fairly icky.
* With console, block and network devices, we can have lots of input which we
* need to process. We could try to tell the kernel what file descriptors to
* watch, but handing a file descriptor mask through to the kernel is fairly
* icky.
*
* Instead, we fork off a process which watches the file descriptors and writes
* the LHREQ_BREAK command to the /dev/lguest filedescriptor to tell the Host
* loop to stop running the Guest. This causes it to return from the
* the LHREQ_BREAK command to the /dev/lguest file descriptor to tell the Host
* stop running the Guest. This causes the Launcher to return from the
* /dev/lguest read with -EAGAIN, where it will write to /dev/lguest to reset
* the LHREQ_BREAK and wake us up again.
*
......@@ -544,7 +546,9 @@ static void wake_parent(int pipefd, int lguest_fd)
if (read(pipefd, &fd, sizeof(fd)) == 0)
exit(0);
/* Otherwise it's telling us to change what file
* descriptors we're to listen to. */
* descriptors we're to listen to. Positive means
* listen to a new one, negative means stop
* listening. */
if (fd >= 0)
FD_SET(fd, &devices.infds);
else
......@@ -559,7 +563,7 @@ static int setup_waker(int lguest_fd)
{
int pipefd[2], child;
/* We create a pipe to talk to the waker, and also so it knows when the
/* We create a pipe to talk to the Waker, and also so it knows when the
* Launcher dies (and closes pipe). */
pipe(pipefd);
child = fork();
......@@ -567,7 +571,8 @@ static int setup_waker(int lguest_fd)
err(1, "forking");
if (child == 0) {
/* Close the "writing" end of our copy of the pipe */
/* We are the Waker: close the "writing" end of our copy of the
* pipe and start waiting for input. */
close(pipefd[1]);
wake_parent(pipefd[0], lguest_fd);
}
......@@ -578,12 +583,12 @@ static int setup_waker(int lguest_fd)
return pipefd[1];
}
/*L:210
/*
* Device Handling.
*
* When the Guest sends DMA to us, it sends us an array of addresses and sizes.
* When the Guest gives us a buffer, it sends an array of addresses and sizes.
* We need to make sure it's not trying to reach into the Launcher itself, so
* we have a convenient routine which check it and exits with an error message
* we have a convenient routine which checks it and exits with an error message
* if something funny is going on:
*/
static void *_check_pointer(unsigned long addr, unsigned int size,
......@@ -600,7 +605,9 @@ static void *_check_pointer(unsigned long addr, unsigned int size,
/* A macro which transparently hands the line number to the real function. */
#define check_pointer(addr,size) _check_pointer(addr, size, __LINE__)
/* This function returns the next descriptor in the chain, or vq->vring.num. */
/* Each buffer in the virtqueues is actually a chain of descriptors. This
* function returns the next descriptor in the chain, or vq->vring.num if we're
* at the end. */
static unsigned next_desc(struct virtqueue *vq, unsigned int i)
{
unsigned int next;
......@@ -679,13 +686,14 @@ static unsigned get_vq_desc(struct virtqueue *vq,
return head;
}
/* Once we've used one of their buffers, we tell them about it. We'll then
/* After we've used one of their buffers, we tell them about it. We'll then
* want to send them an interrupt, using trigger_irq(). */
static void add_used(struct virtqueue *vq, unsigned int head, int len)
{
struct vring_used_elem *used;
/* Get a pointer to the next entry in the used ring. */
/* The virtqueue contains a ring of used buffers. Get a pointer to the
* next entry in that used ring. */
used = &vq->vring.used->ring[vq->vring.used->idx % vq->vring.num];
used->id = head;
used->len = len;
......@@ -699,6 +707,7 @@ static void trigger_irq(int fd, struct virtqueue *vq)
{
unsigned long buf[] = { LHREQ_IRQ, vq->config.irq };
/* If they don't want an interrupt, don't send one. */
if (vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
return;
......@@ -715,8 +724,11 @@ static void add_used_and_trigger(int fd, struct virtqueue *vq,
trigger_irq(fd, vq);
}
/* Here is the input terminal setting we save, and the routine to restore them
* on exit so the user can see what they type next. */
/*
* The Console
*
* Here is the input terminal setting we save, and the routine to restore them
* on exit so the user gets their terminal back. */
static struct termios orig_term;
static void restore_term(void)
{
......@@ -817,7 +829,10 @@ static void handle_console_output(int fd, struct virtqueue *vq)
}
}
/* Handling output for network is also simple: we get all the output buffers
/*
* The Network
*
* 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). */
static void handle_net_output(int fd, struct virtqueue *vq)
......@@ -830,8 +845,9 @@ static void handle_net_output(int fd, struct virtqueue *vq)
while ((head = get_vq_desc(vq, iov, &out, &in)) != vq->vring.num) {
if (in)
errx(1, "Input buffers in output queue?");
/* Check header, but otherwise ignore it (we said we supported
* no features). */
/* Check header, but otherwise ignore it (we told the Guest we
* supported no features, so it shouldn't have anything
* interesting). */
(void)convert(&iov[0], struct virtio_net_hdr);
len = writev(vq->dev->fd, iov+1, out-1);
add_used_and_trigger(fd, vq, head, len);
......@@ -882,7 +898,8 @@ static bool handle_tun_input(int fd, struct device *dev)
return true;
}
/* This callback ensures we try again, in case we stopped console or net
/*L:215 This is the callback attached to the network and console input
* virtqueues: it ensures we try again, in case we stopped console or net
* delivery because Guest didn't have any buffers. */
static void enable_fd(int fd, struct virtqueue *vq)
{
......@@ -918,7 +935,7 @@ static void handle_output(int fd, unsigned long addr)
strnlen(from_guest_phys(addr), guest_limit - addr));
}
/* This is called when the waker wakes us up: check for incoming file
/* This is called when the Waker wakes us up: check for incoming file
* descriptors. */
static void handle_input(int fd)
{
......@@ -985,8 +1002,7 @@ static struct lguest_device_desc *new_dev_desc(u16 type)
}
/* Each device descriptor is followed by some configuration information.
* The first byte is a "status" byte for the Guest to report what's happening.
* After that are fields: u8 type, u8 len, [... len bytes...].
* Each configuration field looks like: u8 type, u8 len, [... len bytes...].
*
* This routine adds a new field to an existing device's descriptor. It only
* works for the last device, but that's OK because that's how we use it. */
......@@ -1043,14 +1059,17 @@ static void add_virtqueue(struct device *dev, unsigned int num_descs,
/* Link virtqueue back to device. */
vq->dev = dev;
/* Set up handler. */
/* Set the routine to call when the Guest does something to this
* virtqueue. */
vq->handle_output = handle_output;
/* Set the "Don't Notify Me" flag if we don't have a handler */
if (!handle_output)
vq->vring.used->flags = VRING_USED_F_NO_NOTIFY;
}
/* This routine does all the creation and setup of a new device, including
* caling new_dev_desc() to allocate the descriptor and device memory. */
* calling new_dev_desc() to allocate the descriptor and device memory. */
static struct device *new_device(const char *name, u16 type, int fd,
bool (*handle_input)(int, struct device *))
{
......@@ -1059,7 +1078,7 @@ static struct device *new_device(const char *name, u16 type, int fd,
/* Append to device list. Prepending to a single-linked list is
* easier, but the user expects the devices to be arranged on the bus
* in command-line order. The first network device on the command line
* is eth0, the first block device /dev/lgba, etc. */
* is eth0, the first block device /dev/vda, etc. */
*devices.lastdev = dev;
dev->next = NULL;
devices.lastdev = &dev->next;
......@@ -1103,7 +1122,7 @@ static void setup_console(void)
/* The console needs two virtqueues: the input then the output. When
* they put something the input queue, we make sure we're listening to
* stdin. When they put something in the output queue, we write it to
* stdout. */
* stdout. */
add_virtqueue(dev, VIRTQUEUE_NUM, enable_fd);
add_virtqueue(dev, VIRTQUEUE_NUM, handle_console_output);
......@@ -1251,21 +1270,17 @@ static void setup_tun_net(const char *arg)
verbose("attached to bridge: %s\n", br_name);
}
/*
* Block device.
/* Our block (disk) device should be really simple: the Guest asks for a block
* number and we read or write that position in the file. Unfortunately, that
* was amazingly slow: the Guest waits until the read is finished before
* running anything else, even if it could have been doing useful work.
*
* Serving a block device is really easy: the Guest asks for a block number and
* we read or write that position in the file.
*
* Unfortunately, this is amazingly slow: the Guest waits until the read is
* finished before running anything else, even if it could be doing useful
* work. We could use async I/O, except it's reputed to suck so hard that
* characters actually go missing from your code when you try to use it.
* We could use async I/O, except it's reputed to suck so hard that characters
* actually go missing from your code when you try to use it.
*
* So we farm the I/O out to thread, and communicate with it via a pipe. */
/* This hangs off device->priv, with the data. */
/* This hangs off device->priv. */
struct vblk_info
{
/* The size of the file. */
......@@ -1281,8 +1296,14 @@ struct vblk_info
* Launcher triggers interrupt to Guest. */
int done_fd;
};
/*:*/
/* This is the core of the I/O thread. It returns true if it did something. */
/*L:210
* The Disk
*
* Remember that the block device is handled by a separate I/O thread. We head
* straight into the core of that thread here:
*/
static bool service_io(struct device *dev)
{
struct vblk_info *vblk = dev->priv;
......@@ -1293,10 +1314,14 @@ static bool service_io(struct device *dev)
struct iovec iov[dev->vq->vring.num];
off64_t off;
/* See if there's a request waiting. If not, nothing to do. */
head = get_vq_desc(dev->vq, iov, &out_num, &in_num);
if (head == dev->vq->vring.num)
return false;
/* Every block request should contain at least one output buffer
* (detailing the location on disk and the type of request) and one
* input buffer (to hold the result). */
if (out_num == 0 || in_num == 0)
errx(1, "Bad virtblk cmd %u out=%u in=%u",
head, out_num, in_num);
......@@ -1305,10 +1330,15 @@ static bool service_io(struct device *dev)
in = convert(&iov[out_num+in_num-1], struct virtio_blk_inhdr);
off = out->sector * 512;
/* This is how we implement barriers. Pretty poor, no? */
/* The block device implements "barriers", where the Guest indicates
* that it wants all previous writes to occur before this write. We
* don't have a way of asking our kernel to do a barrier, so we just
* synchronize all the data in the file. Pretty poor, no? */
if (out->type & VIRTIO_BLK_T_BARRIER)
fdatasync(vblk->fd);
/* In general the virtio block driver is allowed to try SCSI commands.
* It'd be nice if we supported eject, for example, but we don't. */
if (out->type & VIRTIO_BLK_T_SCSI_CMD) {
fprintf(stderr, "Scsi commands unsupported\n");
in->status = VIRTIO_BLK_S_UNSUPP;
......@@ -1374,7 +1404,7 @@ static int io_thread(void *_dev)
/* When this read fails, it means Launcher died, so we follow. */
while (read(vblk->workpipe[0], &c, 1) == 1) {
/* We acknowledge each request immediately, to reduce latency,
/* 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. */
while (service_io(dev))
......@@ -1383,12 +1413,14 @@ static int io_thread(void *_dev)
return 0;
}
/* When the thread says some I/O is done, we interrupt the Guest. */
/* 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. */
static bool handle_io_finish(int fd, struct device *dev)
{
char c;
/* If child died, presumably it printed message. */
/* If the I/O thread died, presumably it printed the error, so we
* simply exit. */
if (read(dev->fd, &c, 1) != 1)
exit(1);
......@@ -1397,7 +1429,7 @@ static bool handle_io_finish(int fd, struct device *dev)
return true;
}
/* When the Guest submits some I/O, we wake the I/O thread. */
/* When the Guest submits some I/O, we just need to wake the I/O thread. */
static void handle_virtblk_output(int fd, struct virtqueue *vq)
{
struct vblk_info *vblk = vq->dev->priv;
......@@ -1409,7 +1441,7 @@ static void handle_virtblk_output(int fd, struct virtqueue *vq)
exit(1);
}
/* This creates a virtual block device. */
/*L:198 This actually sets up a virtual block device. */
static void setup_block_file(const char *filename)
{
int p[2];
......@@ -1425,7 +1457,7 @@ static void setup_block_file(const char *filename)
/* The device responds to return from I/O thread. */
dev = new_device("block", VIRTIO_ID_BLOCK, p[0], handle_io_finish);
/* The device has a virtqueue. */
/* The device has one virtqueue, where the Guest places requests. */
add_virtqueue(dev, VIRTQUEUE_NUM, handle_virtblk_output);
/* Allocate the room for our own bookkeeping */
......@@ -1447,7 +1479,8 @@ static void setup_block_file(const char *filename)
/* The I/O thread writes to this end of the pipe when done. */
vblk->done_fd = p[1];
/* This is how we tell the I/O thread about more work. */
/* This is the second pipe, which is how we tell the I/O thread about
* more work. */
pipe(vblk->workpipe);
/* Create stack for thread and run it */
......@@ -1486,24 +1519,25 @@ static void __attribute__((noreturn)) run_guest(int lguest_fd)
char reason[1024] = { 0 };
read(lguest_fd, reason, sizeof(reason)-1);
errx(1, "%s", reason);
/* EAGAIN means the waker wanted us to look at some input.
/* EAGAIN means the Waker wanted us to look at some input.
* Anything else means a bug or incompatible change. */
} else if (errno != EAGAIN)
err(1, "Running guest failed");
/* Service input, then unset the BREAK which releases
* the Waker. */
/* Service input, then unset the BREAK to release the Waker. */
handle_input(lguest_fd);
if (write(lguest_fd, args, sizeof(args)) < 0)
err(1, "Resetting break");
}
}
/*
* This is the end of the Launcher.
* 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.
*
* But wait! We've seen I/O from the Launcher, and we've seen I/O from the
* Drivers. If we were to see the Host kernel I/O code, our understanding
* would be complete... :*/
* Are you ready? Take a deep breath and join me in the core of the Host, in
* "make Host".
:*/
static struct option opts[] = {
{ "verbose", 0, NULL, 'v' },
......@@ -1526,7 +1560,7 @@ int main(int argc, char *argv[])
/* Memory, top-level pagetable, code startpoint and size of the
* (optional) initrd. */
unsigned long mem = 0, pgdir, start, initrd_size = 0;
/* A temporary and the /dev/lguest file descriptor. */
/* Two temporaries and the /dev/lguest file descriptor. */
int i, c, lguest_fd;
/* The boot information for the Guest. */
struct boot_params *boot;
......@@ -1621,6 +1655,7 @@ int main(int argc, char *argv[])
/* The boot header contains a command line pointer: we put the command
* line after the boot header. */
boot->hdr.cmd_line_ptr = to_guest_phys(boot + 1);
/* We use a simple helper to copy the arguments separated by spaces. */
concat((char *)(boot + 1), argv+optind+2);
/* Boot protocol version: 2.07 supports the fields for lguest. */
......
......@@ -99,7 +99,7 @@ static cycle_t clock_base;
* When lazy_mode is set, it means we're allowed to defer all hypercalls and do
* them as a batch when lazy_mode is eventually turned off. Because hypercalls
* are reasonably expensive, batching them up makes sense. For example, a
* large mmap might update dozens of page table entries: that code calls
* large munmap might update dozens of page table entries: that code calls
* paravirt_enter_lazy_mmu(), does the dozen updates, then calls
* lguest_leave_lazy_mode().
*
......@@ -164,8 +164,8 @@ void async_hcall(unsigned long call,
/*:*/
/*G:033
* Here are our first native-instruction replacements: four functions for
* interrupt control.
* After that diversion we return to our first native-instruction
* replacements: four functions for interrupt control.
*
* The simplest way of implementing these would be to have "turn interrupts
* off" and "turn interrupts on" hypercalls. Unfortunately, this is too slow:
......@@ -184,7 +184,7 @@ static unsigned long save_fl(void)
return lguest_data.irq_enabled;
}
/* "restore_flags" just sets the flags back to the value given. */
/* restore_flags() just sets the flags back to the value given. */
static void restore_fl(unsigned long flags)
{
lguest_data.irq_enabled = flags;
......@@ -357,7 +357,7 @@ static void lguest_cpuid(unsigned int *eax, unsigned int *ebx,
* it. The Host needs to know when the Guest wants to change them, so we have
* a whole series of functions like read_cr0() and write_cr0().
*
* We start with CR0. CR0 allows you to turn on and off all kinds of basic
* We start with cr0. cr0 allows you to turn on and off all kinds of basic
* features, but Linux only really cares about one: the horrifically-named Task
* Switched (TS) bit at bit 3 (ie. 8)
*
......@@ -390,7 +390,7 @@ static void lguest_clts(void)
current_cr0 &= ~X86_CR0_TS;
}
/* CR2 is the virtual address of the last page fault, which the Guest only ever
/* cr2 is the virtual address of the last page fault, which the Guest only ever
* reads. The Host kindly writes this into our "struct lguest_data", so we
* just read it out of there. */
static unsigned long lguest_read_cr2(void)
......@@ -398,7 +398,7 @@ static unsigned long lguest_read_cr2(void)
return lguest_data.cr2;
}
/* CR3 is the current toplevel pagetable page: the principle is the same as
/* cr3 is the current toplevel pagetable page: the principle is the same as
* cr0. Keep a local copy, and tell the Host when it changes. */
static void lguest_write_cr3(unsigned long cr3)
{
......@@ -411,7 +411,7 @@ static unsigned long lguest_read_cr3(void)
return current_cr3;
}
/* CR4 is used to enable and disable PGE, but we don't care. */
/* cr4 is used to enable and disable PGE, but we don't care. */
static unsigned long lguest_read_cr4(void)
{
return 0;
......@@ -432,7 +432,7 @@ static void lguest_write_cr4(unsigned long val)
* maps virtual addresses to physical addresses using "page tables". We could
* use one huge index of 1 million entries: each address is 4 bytes, so that's
* 1024 pages just to hold the page tables. But since most virtual addresses
* are unused, we use a two level index which saves space. The CR3 register
* are unused, we use a two level index which saves space. The cr3 register
* contains the physical address of the top level "page directory" page, which
* contains physical addresses of up to 1024 second-level pages. Each of these
* second level pages contains up to 1024 physical addresses of actual pages,
......@@ -440,7 +440,7 @@ static void lguest_write_cr4(unsigned long val)
*
* Here's a diagram, where arrows indicate physical addresses:
*
* CR3 ---> +---------+
* cr3 ---> +---------+
* | --------->+---------+
* | | | PADDR1 |
* Top-level | | PADDR2 |
......@@ -498,8 +498,7 @@ static void lguest_set_pmd(pmd_t *pmdp, pmd_t pmdval)
*
* ... except in early boot when the kernel sets up the initial pagetables,
* which makes booting astonishingly slow. So we don't even tell the Host
* anything changed until we've done the first page table switch.
*/
* anything changed until we've done the first page table switch. */
static void lguest_set_pte(pte_t *ptep, pte_t pteval)
{
*ptep = pteval;
......@@ -720,10 +719,10 @@ static void lguest_time_init(void)
/* Set up the timer interrupt (0) to go to our simple timer routine */
set_irq_handler(0, lguest_time_irq);
/* Our clock structure look like arch/i386/kernel/tsc.c if we can use
* the TSC, otherwise it's a dumb nanosecond-resolution clock. Either
* way, the "rating" is initialized so high that it's always chosen
* over any other clocksource. */
/* Our clock structure looks like arch/x86/kernel/tsc_32.c if we can
* use the TSC, otherwise it's a dumb nanosecond-resolution clock.
* Either way, the "rating" is set so high that it's always chosen over
* any other clocksource. */
if (lguest_data.tsc_khz)
lguest_clock.mult = clocksource_khz2mult(lguest_data.tsc_khz,
lguest_clock.shift);
......@@ -749,7 +748,7 @@ static void lguest_time_init(void)
* to work. They're pretty simple.
*/
/* The Guest needs to tell the host what stack it expects traps to use. For
/* The Guest needs to tell the Host what stack it expects traps to use. For
* native hardware, this is part of the Task State Segment mentioned above in
* lguest_load_tr_desc(), but to help hypervisors there's this special call.
*
......@@ -850,13 +849,16 @@ static __init char *lguest_memory_setup(void)
return "LGUEST";
}
/* Before virtqueues are set up, we use LHCALL_NOTIFY on normal memory to
* produce console output. */
/* We will eventually use the virtio console device to produce console output,
* but before that is set up we use LHCALL_NOTIFY on normal memory to produce
* console output. */
static __init int early_put_chars(u32 vtermno, const char *buf, int count)
{
char scratch[17];
unsigned int len = count;
/* We use a nul-terminated string, so we have to make a copy. Icky,
* huh? */
if (len > sizeof(scratch) - 1)
len = sizeof(scratch) - 1;
scratch[len] = '\0';
......@@ -883,7 +885,7 @@ static __init int early_put_chars(u32 vtermno, const char *buf, int count)
* Our current solution is to allow the paravirt back end to optionally patch
* over the indirect calls to replace them with something more efficient. We
* patch the four most commonly called functions: disable interrupts, enable
* interrupts, restore interrupts and save interrupts. We usually have 10
* interrupts, restore interrupts and save interrupts. We usually have 6 or 10
* bytes to patch into: the Guest versions of these operations are small enough
* that we can fit comfortably.
*
......@@ -1015,7 +1017,7 @@ __init void lguest_init(void)
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 much it needs in
* Host<->Guest Switcher, and it tells us how big that is in
* lguest_data.reserve_mem, set up on the LGUEST_INIT hypercall. */
reserve_top_address(lguest_data.reserve_mem);
......@@ -1065,6 +1067,6 @@ __init void lguest_init(void)
/*
* This marks the end of stage II of our journey, The Guest.
*
* It is now time for us to explore the nooks and crannies of the three Guest
* devices and complete our understanding of the Guest in "make Drivers".
* It is now time for us to explore the layer of virtual drivers and complete
* our understanding of the Guest in "make Drivers".
*/
......@@ -6,7 +6,7 @@
#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. The boot header is in %esi.
* type field is "1" (lguest), so 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
......@@ -17,13 +17,15 @@
* boot. */
.section .init.text, "ax", @progbits
ENTRY(lguest_entry)
/* Make initial hypercall now, so we can set up the pagetables. */
/* We make the "initialization" hypercall now to tell the Host about
* us, and also find out where it put our page tables. */
movl $LHCALL_LGUEST_INIT, %eax
movl $lguest_data - __PAGE_OFFSET, %edx
int $LGUEST_TRAP_ENTRY
/* The Host put the toplevel pagetable in lguest_data.pgdir. The movsl
* instruction uses %esi implicitly. */
* instruction uses %esi implicitly as the source for the copy we'
* about to do. */
movl lguest_data - __PAGE_OFFSET + LGUEST_DATA_pgdir, %esi
/* Copy first 32 entries of page directory to __PAGE_OFFSET entries.
......
......@@ -128,9 +128,12 @@ static void unmap_switcher(void)
__free_pages(switcher_page[i], 0);
}
/*L:305
/*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.
......
......@@ -90,6 +90,7 @@ static void do_hcall(struct lguest *lg, struct hcall_args *args)
lg->pending_notify = args->arg1;
break;
default:
/* It should be an architecture-specific hypercall. */
if (lguest_arch_do_hcall(lg, args))
kill_guest(lg, "Bad hypercall %li\n", args->arg0);
}
......@@ -157,7 +158,6 @@ static void do_async_hcalls(struct lguest *lg)
* Guest makes a hypercall, we end up here to set things up: */
static void initialize(struct lguest *lg)
{
/* You can't do anything until you're initialized. The Guest knows the
* rules, so we're unforgiving here. */
if (lg->hcall->arg0 != LHCALL_LGUEST_INIT) {
......@@ -174,7 +174,8 @@ static void initialize(struct lguest *lg)
|| get_user(lg->noirq_end, &lg->lguest_data->noirq_end))
kill_guest(lg, "bad guest page %p", lg->lguest_data);
/* We write the current time into the Guest's data page once now. */
/* We write the current time into the Guest's data page once so it can
* set its clock. */
write_timestamp(lg);
/* page_tables.c will also do some setup. */