/*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; } static void lg_set_features(struct virtio_device *vdev, u32 features) { unsigned int i; 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; memset(out_features, 0, desc->feature_len); for (i = 0; i < min(desc->feature_len * 8, 32); i++) { if (features & (1 << i)) 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, .set_features = lg_set_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?". */