lguest_device.c

Go to the documentation of this file.

/*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 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" or two to send and receive data.
:*/
#include <linux/init.h>
#include <linux/bootmem.h>
#include <linux/lguest_launcher.h>
#include <linux/virtio.h>
#include <linux/virtio_config.h>
#include <linux/interrupt.h>
#include <linux/virtio_ring.h>
#include <linux/err.h>
#include <linux/export.h>
#include <linux/slab.h>
#include <asm/io.h>
#include <asm/paravirt.h>
#include <asm/lguest_hcall.h>

/* The pointer to our (page) of device descriptions. */
static void *lguest_devices;

/*
 * For Guests, device memory can be used as normal memory, so we cast away the
 * __iomem to quieten sparse.
 */
static inline void *lguest_map(unsigned long phys_addr, unsigned long pages)
{
    return (__force void *)ioremap_cache(phys_addr, PAGE_SIZE*pages);
}

static inline void lguest_unmap(void *addr)
{
    iounmap((__force void __iomem *)addr);
}

/*D:100
 * Each lguest device is just a virtio device plus a pointer to its entry
 * in the lguest_devices page.
 */
struct lguest_device {
    struct virtio_device vdev;

    /* The entry in the lguest_devices page for this device. */
    struct lguest_device_desc *desc;
};

/*
 * Since the virtio infrastructure hands us a pointer to the virtio_device all
 * the time, it helps to have a curt macro to get a pointer to the struct
 * lguest_device it's enclosed in.
 */
#define to_lgdev(vd) container_of(vd, struct lguest_device, vdev)

/*D:130
 * Device configurations
 *
 * The configuration information for a device consists of one or more
 * 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.
 *
 * A convenient routine to return the device's virtqueue config array:
 * immediately after the descriptor.
 */
static struct lguest_vqconfig *lg_vq(const struct lguest_device_desc *desc)
{
    return (void *)(desc + 1);
}

/* The features come immediately after the virtqueues. */
static u8 *lg_features(const struct lguest_device_desc *desc)
{
    return (void *)(lg_vq(desc) + desc->num_vq);
}

/* The config space comes after the two feature bitmasks. */
static u8 *lg_config(const struct lguest_device_desc *desc)
{
    return lg_features(desc) + desc->feature_len * 2;
}

/* The total size of the config page used by this device (incl. desc) */
static unsigned desc_size(const struct lguest_device_desc *desc)
{
    return sizeof(*desc)
        + desc->num_vq * sizeof(struct lguest_vqconfig)
        + desc->feature_len * 2
        + desc->config_len;
}

/* This gets the device's feature bits. */
static u32 lg_get_features(struct virtio_device *vdev)
{
    unsigned int i;
    u32 features = 0;
    struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
    u8 *in_features = lg_features(desc);

    /* We do this the slow but generic way. */
    for (i = 0; i < min(desc->feature_len * 8, 32); i++)
        if (in_features[i / 8] & (1 << (i % 8)))
            features |= (1 << i);

    return features;
}

/*
 * To notify on reset or feature finalization, we (ab)use the NOTIFY
 * hypercall, with the descriptor address of the device.
 */
static void status_notify(struct virtio_device *vdev)
{
    unsigned long offset = (void *)to_lgdev(vdev)->desc - lguest_devices;

    hcall(LHCALL_NOTIFY, (max_pfn << PAGE_SHIFT) + offset, 0, 0, 0);
}

/*
 * The virtio core takes the features the Host offers, and copies the ones
 * supported by the driver into the vdev->features array.  Once that's all
 * sorted out, this routine is called so we can tell the Host which features we
 * understand and accept.
 */
static void lg_finalize_features(struct virtio_device *vdev)
{
    unsigned int i, bits;
    struct lguest_device_desc *desc = to_lgdev(vdev)->desc;
    /* Second half of bitmap is features we accept. */
    u8 *out_features = lg_features(desc) + desc->feature_len;

    /* Give virtio_ring a chance to accept features. */
    vring_transport_features(vdev);

    /*
     * The vdev->feature array is a Linux bitmask: this isn't the same as a
     * the simple array of bits used by lguest devices for features.  So we
     * do this slow, manual conversion which is completely general.
     */
    memset(out_features, 0, desc->feature_len);
    bits = min_t(unsigned, desc->feature_len, sizeof(vdev->features)) * 8;
    for (i = 0; i < bits; i++) {
        if (test_bit(i, vdev->features))
            out_features[i / 8] |= (1 << (i % 8));
    }

    /* Tell Host we've finished with this device's feature negotiation */
    status_notify(vdev);
}

/* Once they've found a field, getting a copy of it is easy. */
static void lg_get(struct virtio_device *vdev, unsigned int offset,
           void *buf, unsigned len)
{
    struct lguest_device_desc *desc = to_lgdev(vdev)->desc;

    /* Check they didn't ask for more than the length of the config! */
    BUG_ON(offset + len > desc->config_len);
    memcpy(buf, lg_config(desc) + offset, len);
}

/* Setting the contents is also trivial. */
static void lg_set(struct virtio_device *vdev, unsigned int offset,
           const void *buf, unsigned len)
{
    struct lguest_device_desc *desc = to_lgdev(vdev)->desc;

    /* Check they didn't ask for more than the length of the config! */
    BUG_ON(offset + len > desc->config_len);
    memcpy(lg_config(desc) + offset, buf, len);
}

/*
 * The operations to get and set the status word just access the status field
 * of the device descriptor.
 */
static u8 lg_get_status(struct virtio_device *vdev)
{
    return to_lgdev(vdev)->desc->status;
}

static void lg_set_status(struct virtio_device *vdev, u8 status)
{
    BUG_ON(!status);
    to_lgdev(vdev)->desc->status = status;

    /* Tell Host immediately if we failed. */
    if (status & VIRTIO_CONFIG_S_FAILED)
        status_notify(vdev);
}

static void lg_reset(struct virtio_device *vdev)
{
    /* 0 status means "reset" */
    to_lgdev(vdev)->desc->status = 0;
    status_notify(vdev);
}

/*
 * Virtqueues
 *
 * The other piece of infrastructure virtio needs is a "virtqueue": a way of
 * the Guest device registering buffers for the other side to read from or
 * write into (ie. send and receive buffers).  Each device can have multiple
 * virtqueues: for example the console driver uses one queue for sending and
 * another for receiving.
 *
 * Fortunately for us, a very fast shared-memory-plus-descriptors virtqueue
 * already exists in virtio_ring.c.  We just need to connect it up.
 *
 * We start with the information we need to keep about each virtqueue.
 */

/*D:140 This is the information we remember about each virtqueue. */
struct lguest_vq_info {
    /* A copy of the information contained in the device config. */
    struct lguest_vqconfig config;

    /* The address where we mapped the virtio ring, so we can unmap it. */
    void *pages;
};

/*
 * When the virtio_ring code wants to prod the Host, it calls us here and we
 * 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)
{
    /*
     * We store our virtqueue information in the "priv" pointer of the
     * virtqueue structure.
     */
    struct lguest_vq_info *lvq = vq->priv;

    hcall(LHCALL_NOTIFY, lvq->config.pfn << PAGE_SHIFT, 0, 0, 0);
}

/* An extern declaration inside a C file is bad form.  Don't do it. */
extern int lguest_setup_irq(unsigned int irq);

/*
 * This routine finds the Nth virtqueue described in the configuration of
 * this device and sets it up.
 *
 * This is kind of an ugly duckling.  It'd be nicer to have a standard
 * representation of a virtqueue in the configuration space, but it seems that
 * everyone wants to do it differently.  The KVM coders want the Guest to
 * 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.
 */
static struct virtqueue *lg_find_vq(struct virtio_device *vdev,
                    unsigned index,
                    void (*callback)(struct virtqueue *vq),
                    const char *name)
{
    struct lguest_device *ldev = to_lgdev(vdev);
    struct lguest_vq_info *lvq;
    struct virtqueue *vq;
    int err;

    if (!name)
        return NULL;

    /* We must have this many virtqueues. */
    if (index >= ldev->desc->num_vq)
        return ERR_PTR(-ENOENT);

    lvq = kmalloc(sizeof(*lvq), GFP_KERNEL);
    if (!lvq)
        return ERR_PTR(-ENOMEM);

    /*
     * Make a copy of the "struct lguest_vqconfig" entry, which sits after
     * the descriptor.  We need a copy because the config space might not
     * be aligned correctly.
     */
    memcpy(&lvq->config, lg_vq(ldev->desc)+index, sizeof(lvq->config));

    printk("Mapping virtqueue %i addr %lx\n", index,
           (unsigned long)lvq->config.pfn << PAGE_SHIFT);
    /* Figure out how many pages the ring will take, and map that memory */
    lvq->pages = lguest_map((unsigned long)lvq->config.pfn << PAGE_SHIFT,
                DIV_ROUND_UP(vring_size(lvq->config.num,
                            LGUEST_VRING_ALIGN),
                         PAGE_SIZE));
    if (!lvq->pages) {
        err = -ENOMEM;
        goto free_lvq;
    }

    /*
     * OK, tell virtio_ring.c to set up a virtqueue now we know its size
     * and we've got a pointer to its pages.  Note that we set weak_barriers
     * to 'true': the host just a(nother) SMP CPU, so we only need inter-cpu
     * barriers.
     */
    vq = vring_new_virtqueue(index, lvq->config.num, LGUEST_VRING_ALIGN, vdev,
                 true, lvq->pages, lg_notify, callback, name);
    if (!vq) {
        err = -ENOMEM;
        goto unmap;
    }

    /* Make sure the interrupt is allocated. */
    err = lguest_setup_irq(lvq->config.irq);
    if (err)
        goto destroy_vring;

    /*
     * Tell the interrupt for this virtqueue to go to the virtio_ring
     * interrupt handler.
     *
     * FIXME: We used to have a flag for the Host to tell us we could use
     * the interrupt as a source of randomness: it'd be nice to have that
     * back.
     */
    err = request_irq(lvq->config.irq, vring_interrupt, IRQF_SHARED,
              dev_name(&vdev->dev), vq);
    if (err)
        goto free_desc;

    /*
     * Last of all we hook up our 'struct lguest_vq_info" to the
     * virtqueue's priv pointer.
     */
    vq->priv = lvq;
    return vq;

free_desc:
    irq_free_desc(lvq->config.irq);
destroy_vring:
    vring_del_virtqueue(vq);
unmap:
    lguest_unmap(lvq->pages);
free_lvq:
    kfree(lvq);
    return ERR_PTR(err);
}
/*:*/

/* Cleaning up a virtqueue is easy */
static void lg_del_vq(struct virtqueue *vq)
{
    struct lguest_vq_info *lvq = vq->priv;

    /* Release the interrupt */
    free_irq(lvq->config.irq, vq);
    /* Tell virtio_ring.c to free the virtqueue. */
    vring_del_virtqueue(vq);
    /* Unmap the pages containing the ring. */
    lguest_unmap(lvq->pages);
    /* Free our own queue information. */
    kfree(lvq);
}

static void lg_del_vqs(struct virtio_device *vdev)
{
    struct virtqueue *vq, *n;

    list_for_each_entry_safe(vq, n, &vdev->vqs, list)
        lg_del_vq(vq);
}

static int lg_find_vqs(struct virtio_device *vdev, unsigned nvqs,
               struct virtqueue *vqs[],
               vq_callback_t *callbacks[],
               const char *names[])
{
    struct lguest_device *ldev = to_lgdev(vdev);
    int i;

    /* We must have this many virtqueues. */
    if (nvqs > ldev->desc->num_vq)
        return -ENOENT;

    for (i = 0; i < nvqs; ++i) {
        vqs[i] = lg_find_vq(vdev, i, callbacks[i], names[i]);
        if (IS_ERR(vqs[i]))
            goto error;
    }
    return 0;

error:
    lg_del_vqs(vdev);
    return PTR_ERR(vqs[i]);
}

static const char *lg_bus_name(struct virtio_device *vdev)
{
    return "";
}

/* The ops structure which hooks everything together. */
static struct virtio_config_ops lguest_config_ops = {
    .get_features = lg_get_features,
    .finalize_features = lg_finalize_features,
    .get = lg_get,
    .set = lg_set,
    .get_status = lg_get_status,
    .set_status = lg_set_status,
    .reset = lg_reset,
    .find_vqs = lg_find_vqs,
    .del_vqs = lg_del_vqs,
    .bus_name = lg_bus_name,
};

/*
 * The root device for the lguest virtio devices.  This makes them appear as
 * /sys/devices/lguest/0,1,2 not /sys/devices/0,1,2.
 */
static struct device *lguest_root;

/*D:120
 * This is the core of the lguest bus: actually adding a new device.
 * It's a separate function because it's neater that way, and because an
 * earlier version of the code supported hotplug and unplug.  They were removed
 * early on because they were never used.
 *
 * As Andrew Tridgell says, "Untested code is buggy code".
 *
 * It's worth reading this carefully: we start with a pointer to the new device
 * descriptor in the "lguest_devices" page, and the offset into the device
 * descriptor page so we can uniquely identify it if things go badly wrong.
 */
static void add_lguest_device(struct lguest_device_desc *d,
                  unsigned int offset)
{
    struct lguest_device *ldev;

    /* Start with zeroed memory; Linux's device layer counts on it. */
    ldev = kzalloc(sizeof(*ldev), GFP_KERNEL);
    if (!ldev) {
        printk(KERN_EMERG "Cannot allocate lguest dev %u type %u\n",
               offset, d->type);
        return;
    }

    /* This devices' parent is the lguest/ dir. */
    ldev->vdev.dev.parent = lguest_root;
    /*
     * The device type comes straight from the descriptor.  There's also a
     * device vendor field in the virtio_device struct, which we leave as
     * 0.
     */
    ldev->vdev.id.device = d->type;
    /*
     * We have a simple set of routines for querying the device's
     * configuration information and setting its status.
     */
    ldev->vdev.config = &lguest_config_ops;
    /* And we remember the device's descriptor for lguest_config_ops. */
    ldev->desc = d;

    /*
     * register_virtio_device() sets up the generic fields for the struct
     * virtio_device and calls device_register().  This makes the bus
     * infrastructure look for a matching driver.
     */
    if (register_virtio_device(&ldev->vdev) != 0) {
        printk(KERN_ERR "Failed to register lguest dev %u type %u\n",
               offset, d->type);
        kfree(ldev);
    }
}

/*D:110
 * scan_devices() simply iterates through the device page.  The type 0 is
 * reserved to mean "end of devices".
 */
static void scan_devices(void)
{
    unsigned int i;
    struct lguest_device_desc *d;

    /* We start at the page beginning, and skip over each entry. */
    for (i = 0; i < PAGE_SIZE; i += desc_size(d)) {
        d = lguest_devices + i;

        /* Once we hit a zero, stop. */
        if (d->type == 0)
            break;

        printk("Device at %i has size %u\n", i, desc_size(d));
        add_lguest_device(d, i);
    }
}

/*D:105
 * Fairly early in boot, lguest_devices_init() is called to set up the
 * lguest device infrastructure.  We check that we are a Guest by checking
 * pv_info.name: there are other ways of checking, but this seems most
 * obvious to me.
 *
 * So we can access the "struct lguest_device_desc"s easily, we map that memory
 * and store the pointer in the global "lguest_devices".  Then we register a
 * root device from which all our devices will hang (this seems to be the
 * correct sysfs incantation).
 *
 * Finally we call scan_devices() which adds all the devices found in the
 * lguest_devices page.
 */
static int __init lguest_devices_init(void)
{
    if (strcmp(pv_info.name, "lguest") != 0)
        return 0;

    lguest_root = root_device_register("lguest");
    if (IS_ERR(lguest_root))
        panic("Could not register lguest root");

    /* Devices are in a single page above top of "normal" mem */
    lguest_devices = lguest_map(max_pfn<<PAGE_SHIFT, 1);

    scan_devices();
    return 0;
}
/* We do this after core stuff, but before the drivers. */
postcore_initcall(lguest_devices_init);

/*D:150
 * At this point in the journey we used to now wade through the lguest
 * devices themselves: net, block and console.  Since they're all now virtio
 * devices rather than lguest-specific, I've decided to ignore them.  Mostly,
 * they're kind of boring.  But this does mean you'll never experience the
 * thrill of reading the forbidden love scene buried deep in the block driver.
 *
 * "make Launcher" beckons, where we answer questions like "Where do Guests
 * come from?", and "What do you do when someone asks for optimization?".
 */