diff options
Diffstat (limited to 'drivers/lguest/lguest_device.c')
| -rw-r--r-- | drivers/lguest/lguest_device.c | 429 |
1 files changed, 429 insertions, 0 deletions
diff --git a/drivers/lguest/lguest_device.c b/drivers/lguest/lguest_device.c new file mode 100644 index 0000000..a661bbd --- /dev/null +++ b/drivers/lguest/lguest_device.c @@ -0,0 +1,429 @@ +/*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 <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; +} + +/* 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)); + } +} + +/* 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; +} + +/* To notify on status updates, we (ab)use the NOTIFY hypercall, with the + * descriptor address of the device. A zero status means "reset". */ +static void set_status(struct virtio_device *vdev, u8 status) +{ + unsigned long offset = (void *)to_lgdev(vdev)->desc - lguest_devices; + + /* We set the status. */ + to_lgdev(vdev)->desc->status = status; + hcall(LHCALL_NOTIFY, (max_pfn<<PAGE_SHIFT) + offset, 0, 0); +} + +static void lg_set_status(struct virtio_device *vdev, u8 status) +{ + BUG_ON(!status); + set_status(vdev, status); +} + +static void lg_reset(struct virtio_device *vdev) +{ + set_status(vdev, 0); +} + +/* + * 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); +} + +/* This routine finds the first 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. + * + * 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)) +{ + struct lguest_device *ldev = to_lgdev(vdev); + struct lguest_vq_info *lvq; + struct virtqueue *vq; + int err; + + /* 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, + PAGE_SIZE), + 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. */ + vq = vring_new_virtqueue(lvq->config.num, vdev, lvq->pages, + lg_notify, callback); + if (!vq) { + err = -ENOMEM; + goto unmap; + } + + /* 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, + vdev->dev.bus_id, vq); + if (err) + goto destroy_vring; + + /* Last of all we hook up our 'struct lguest_vq_info" to the + * virtqueue's priv pointer. */ + vq->priv = lvq; + return vq; + +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); +} + +/* 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_vq = lg_find_vq, + .del_vq = lg_del_vq, +}; + +/* 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 = { + .parent = NULL, + .bus_id = "lguest", +}; + +/*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 seems to count 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; + /* We have a unique device index thanks to the dev_index counter. */ + 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; + + if (device_register(&lguest_root) != 0) + 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?". */ |
