diff options
author | Rusty Russell <rusty@rustcorp.com.au> | 2007-10-25 15:02:50 +1000 |
---|---|---|
committer | Rusty Russell <rusty@rustcorp.com.au> | 2007-10-25 15:02:50 +1000 |
commit | e1e72965ec2c02db99b415cd06c17ea90767e3a4 (patch) | |
tree | 94e43aac35bdc33220e64f285b72b3b2b787fd57 | |
parent | 568a17ffce2eeceae0cd9fc37e97cbad12f70278 (diff) |
lguest: documentation update
Went through the documentation doing typo and content fixes. This
patch contains only comment and whitespace changes.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
-rw-r--r-- | Documentation/lguest/lguest.c | 155 | ||||
-rw-r--r-- | arch/x86/lguest/boot.c | 48 | ||||
-rw-r--r-- | arch/x86/lguest/i386_head.S | 8 | ||||
-rw-r--r-- | drivers/lguest/core.c | 5 | ||||
-rw-r--r-- | drivers/lguest/hypercalls.c | 11 | ||||
-rw-r--r-- | drivers/lguest/interrupts_and_traps.c | 37 | ||||
-rw-r--r-- | drivers/lguest/lg.h | 4 | ||||
-rw-r--r-- | drivers/lguest/lguest_device.c | 11 | ||||
-rw-r--r-- | drivers/lguest/lguest_user.c | 23 | ||||
-rw-r--r-- | drivers/lguest/page_tables.c | 113 | ||||
-rw-r--r-- | drivers/lguest/segments.c | 48 | ||||
-rw-r--r-- | drivers/lguest/x86/core.c | 120 | ||||
-rw-r--r-- | drivers/lguest/x86/switcher_32.S | 71 | ||||
-rw-r--r-- | include/asm-x86/lguest_hcall.h | 16 | ||||
-rw-r--r-- | include/linux/lguest.h | 4 | ||||
-rw-r--r-- | include/linux/lguest_launcher.h | 6 |
16 files changed, 414 insertions, 266 deletions
diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c index c91c28ae8290..f2668390e8f7 100644 --- a/Documentation/lguest/lguest.c +++ b/Documentation/lguest/lguest.c @@ -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. */ diff --git a/arch/x86/lguest/boot.c b/arch/x86/lguest/boot.c index a0179fc6b791..a55b0902f9d3 100644 --- a/arch/x86/lguest/boot.c +++ b/arch/x86/lguest/boot.c @@ -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". */ diff --git a/arch/x86/lguest/i386_head.S b/arch/x86/lguest/i386_head.S index ebc6ac733899..95b6fbcded63 100644 --- a/arch/x86/lguest/i386_head.S +++ b/arch/x86/lguest/i386_head.S @@ -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. diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c index 35d19ae58de7..cb4c67025d52 100644 --- a/drivers/lguest/core.c +++ b/drivers/lguest/core.c @@ -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. diff --git a/drivers/lguest/hypercalls.c b/drivers/lguest/hypercalls.c index 9d5184c7c14a..b478affe8f91 100644 --- a/drivers/lguest/hypercalls.c +++ b/drivers/lguest/hypercalls.c @@ -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. */ @@ -182,8 +183,8 @@ static void initialize(struct lguest *lg) /* This is the one case where the above accesses might have been the * first write to a Guest page. This may have caused a copy-on-write - * fault, but the Guest might be referring to the old (read-only) - * page. */ + * fault, but the old page might be (read-only) in the Guest + * pagetable. */ guest_pagetable_clear_all(lg); } @@ -220,7 +221,7 @@ void do_hypercalls(struct lguest *lg) * Normally it doesn't matter: the Guest will run again and * update the trap number before we come back here. * - * However, if we are signalled or the Guest sends DMA to the + * 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. */ diff --git a/drivers/lguest/interrupts_and_traps.c b/drivers/lguest/interrupts_and_traps.c index 82966982cb38..2b66f79c208b 100644 --- a/drivers/lguest/interrupts_and_traps.c +++ b/drivers/lguest/interrupts_and_traps.c @@ -92,8 +92,8 @@ static void set_guest_interrupt(struct lguest *lg, u32 lo, u32 hi, int has_err) /* Remember that we never let the Guest actually disable interrupts, so * the "Interrupt Flag" bit is always set. We copy that bit from the - * Guest's "irq_enabled" field into the eflags word: the Guest copies - * it back in "lguest_iret". */ + * Guest's "irq_enabled" field into the eflags word: we saw the Guest + * copy it back in "lguest_iret". */ eflags = lg->regs->eflags; if (get_user(irq_enable, &lg->lguest_data->irq_enabled) == 0 && !(irq_enable & X86_EFLAGS_IF)) @@ -124,7 +124,7 @@ static void set_guest_interrupt(struct lguest *lg, u32 lo, u32 hi, int has_err) kill_guest(lg, "Disabling interrupts"); } -/*H:200 +/*H:205 * Virtual Interrupts. * * maybe_do_interrupt() gets called before every entry to the Guest, to see if @@ -256,19 +256,21 @@ int deliver_trap(struct lguest *lg, unsigned int num) * bogus one in): if we fail here, the Guest will be killed. */ if (!idt_present(lg->arch.idt[num].a, lg->arch.idt[num].b)) return 0; - set_guest_interrupt(lg, lg->arch.idt[num].a, lg->arch.idt[num].b, has_err(num)); + set_guest_interrupt(lg, lg->arch.idt[num].a, lg->arch.idt[num].b, + has_err(num)); return 1; } /*H:250 Here's the hard part: returning to the Host every time a trap happens * and then calling deliver_trap() and re-entering the Guest is slow. - * Particularly because Guest userspace system calls are traps (trap 128). + * Particularly because Guest userspace system calls are traps (usually trap + * 128). * * So we'd like to set up the IDT to tell the CPU to deliver traps directly * into the Guest. This is possible, but the complexities cause the size of * this file to double! However, 150 lines of code is worth writing for taking * system calls down from 1750ns to 270ns. Plus, if lguest didn't do it, all - * the other hypervisors would tease it. + * the other hypervisors would beat it up at lunchtime. * * This routine indicates if a particular trap number could be delivered * directly. */ @@ -331,7 +333,7 @@ void pin_stack_pages(struct lguest *lg) * change stacks on each context switch. */ void guest_set_stack(struct lguest *lg, u32 seg, u32 esp, unsigned int pages) { - /* You are not allowd have a stack segment with privilege level 0: bad + /* You are not allowed have a stack segment with privilege level 0: bad * Guest! */ if ((seg & 0x3) != GUEST_PL) kill_guest(lg, "bad stack segment %i", seg); @@ -350,7 +352,7 @@ void guest_set_stack(struct lguest *lg, u32 seg, u32 esp, unsigned int pages) * part of the Host: page table handling. */ /*H:235 This is the routine which actually checks the Guest's IDT entry and - * transfers it into our entry in "struct lguest": */ + * transfers it into the entry in "struct lguest": */ static void set_trap(struct lguest *lg, struct desc_struct *trap, unsigned int num, u32 lo, u32 hi) { @@ -456,6 +458,18 @@ void copy_traps(const struct lguest *lg, struct desc_struct *idt, } } +/*H:200 + * The Guest Clock. + * + * There are two sources of virtual interrupts. We saw one in lguest_user.c: + * the Launcher sending interrupts for virtual devices. The other is the Guest + * timer interrupt. + * + * The Guest uses the LHCALL_SET_CLOCKEVENT hypercall to tell us how long to + * the next timer interrupt (in nanoseconds). We use the high-resolution timer + * infrastructure to set a callback at that time. + * + * 0 means "turn off the clock". */ void guest_set_clockevent(struct lguest *lg, unsigned long delta) { ktime_t expires; @@ -466,20 +480,27 @@ void guest_set_clockevent(struct lguest *lg, unsigned long delta) return; } + /* We use wallclock time here, so the Guest might not be running for + * all the time between now and the timer interrupt it asked for. This + * is almost always the right thing to do. */ expires = ktime_add_ns(ktime_get_real(), delta); hrtimer_start(&lg->hrt, expires, HRTIMER_MODE_ABS); } +/* This is the function called when the Guest's timer expires. */ static enum hrtimer_restart clockdev_fn(struct hrtimer *timer) { struct lguest *lg = container_of(timer, struct lguest, hrt); + /* Remember the first interrupt is the timer interrupt. */ set_bit(0, lg->irqs_pending); + /* If the Guest is actually stopped, we need to wak |