diff options
Diffstat (limited to 'drivers/lguest/io.c')
| -rw-r--r-- | drivers/lguest/io.c | 626 |
1 files changed, 626 insertions, 0 deletions
diff --git a/drivers/lguest/io.c b/drivers/lguest/io.c new file mode 100644 index 0000000..ea68613 --- /dev/null +++ b/drivers/lguest/io.c @@ -0,0 +1,626 @@ +/*P:300 The I/O mechanism in lguest is simple yet flexible, allowing the Guest + * to talk to the Launcher or directly to another Guest. It uses familiar + * concepts of DMA and interrupts, plus some neat code stolen from + * futexes... :*/ + +/* Copyright (C) 2006 Rusty Russell IBM Corporation + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA + */ +#include <linux/types.h> +#include <linux/futex.h> +#include <linux/jhash.h> +#include <linux/mm.h> +#include <linux/highmem.h> +#include <linux/uaccess.h> +#include "lg.h" + +/*L:300 + * I/O + * + * Getting data in and out of the Guest is quite an art. There are numerous + * ways to do it, and they all suck differently. We try to keep things fairly + * close to "real" hardware so our Guest's drivers don't look like an alien + * visitation in the middle of the Linux code, and yet make sure that Guests + * can talk directly to other Guests, not just the Launcher. + * + * To do this, the Guest gives us a key when it binds or sends DMA buffers. + * The key corresponds to a "physical" address inside the Guest (ie. a virtual + * address inside the Launcher process). We don't, however, use this key + * directly. + * + * We want Guests which share memory to be able to DMA to each other: two + * Launchers can mmap memory the same file, then the Guests can communicate. + * Fortunately, the futex code provides us with a way to get a "union + * futex_key" corresponding to the memory lying at a virtual address: if the + * two processes share memory, the "union futex_key" for that memory will match + * even if the memory is mapped at different addresses in each. So we always + * convert the keys to "union futex_key"s to compare them. + * + * Before we dive into this though, we need to look at another set of helper + * routines used throughout the Host kernel code to access Guest memory. + :*/ +static struct list_head dma_hash[61]; + +/* An unfortunate side effect of the Linux double-linked list implementation is + * that there's no good way to statically initialize an array of linked + * lists. */ +void lguest_io_init(void) +{ + unsigned int i; + + for (i = 0; i < ARRAY_SIZE(dma_hash); i++) + INIT_LIST_HEAD(&dma_hash[i]); +} + +/* FIXME: allow multi-page lengths. */ +static int check_dma_list(struct lguest *lg, const struct lguest_dma *dma) +{ + unsigned int i; + + for (i = 0; i < LGUEST_MAX_DMA_SECTIONS; i++) { + if (!dma->len[i]) + return 1; + if (!lguest_address_ok(lg, dma->addr[i], dma->len[i])) + goto kill; + if (dma->len[i] > PAGE_SIZE) + goto kill; + /* We could do over a page, but is it worth it? */ + if ((dma->addr[i] % PAGE_SIZE) + dma->len[i] > PAGE_SIZE) + goto kill; + } + return 1; + +kill: + kill_guest(lg, "bad DMA entry: %u@%#lx", dma->len[i], dma->addr[i]); + return 0; +} + +/*L:330 This is our hash function, using the wonderful Jenkins hash. + * + * The futex key is a union with three parts: an unsigned long word, a pointer, + * and an int "offset". We could use jhash_2words() which takes three u32s. + * (Ok, the hash functions are great: the naming sucks though). + * + * It's nice to be portable to 64-bit platforms, so we use the more generic + * jhash2(), which takes an array of u32, the number of u32s, and an initial + * u32 to roll in. This is uglier, but breaks down to almost the same code on + * 32-bit platforms like this one. + * + * We want a position in the array, so we modulo ARRAY_SIZE(dma_hash) (ie. 61). + */ +static unsigned int hash(const union futex_key *key) +{ + return jhash2((u32*)&key->both.word, + (sizeof(key->both.word)+sizeof(key->both.ptr))/4, + key->both.offset) + % ARRAY_SIZE(dma_hash); +} + +/* This is a convenience routine to compare two keys. It's a much bemoaned C + * weakness that it doesn't allow '==' on structures or unions, so we have to + * open-code it like this. */ +static inline int key_eq(const union futex_key *a, const union futex_key *b) +{ + return (a->both.word == b->both.word + && a->both.ptr == b->both.ptr + && a->both.offset == b->both.offset); +} + +/*L:360 OK, when we need to actually free up a Guest's DMA array we do several + * things, so we have a convenient function to do it. + * + * The caller must hold a read lock on dmainfo owner's current->mm->mmap_sem + * for the drop_futex_key_refs(). */ +static void unlink_dma(struct lguest_dma_info *dmainfo) +{ + /* You locked this too, right? */ + BUG_ON(!mutex_is_locked(&lguest_lock)); + /* This is how we know that the entry is free. */ + dmainfo->interrupt = 0; + /* Remove it from the hash table. */ + list_del(&dmainfo->list); + /* Drop the references we were holding (to the inode or mm). */ + drop_futex_key_refs(&dmainfo->key); +} + +/*L:350 This is the routine which we call when the Guest asks to unregister a + * DMA array attached to a given key. Returns true if the array was found. */ +static int unbind_dma(struct lguest *lg, + const union futex_key *key, + unsigned long dmas) +{ + int i, ret = 0; + + /* We don't bother with the hash table, just look through all this + * Guest's DMA arrays. */ + for (i = 0; i < LGUEST_MAX_DMA; i++) { + /* In theory it could have more than one array on the same key, + * or one array on multiple keys, so we check both */ + if (key_eq(key, &lg->dma[i].key) && dmas == lg->dma[i].dmas) { + unlink_dma(&lg->dma[i]); + ret = 1; + break; + } + } + return ret; +} + +/*L:340 BIND_DMA: this is the hypercall which sets up an array of "struct + * lguest_dma" for receiving I/O. + * + * The Guest wants to bind an array of "struct lguest_dma"s to a particular key + * to receive input. This only happens when the Guest is setting up a new + * device, so it doesn't have to be very fast. + * + * It returns 1 on a successful registration (it can fail if we hit the limit + * of registrations for this Guest). + */ +int bind_dma(struct lguest *lg, + unsigned long ukey, unsigned long dmas, u16 numdmas, u8 interrupt) +{ + unsigned int i; + int ret = 0; + union futex_key key; + /* Futex code needs the mmap_sem. */ + struct rw_semaphore *fshared = ¤t->mm->mmap_sem; + + /* Invalid interrupt? (We could kill the guest here). */ + if (interrupt >= LGUEST_IRQS) + return 0; + + /* We need to grab the Big Lguest Lock, because other Guests may be + * trying to look through this Guest's DMAs to send something while + * we're doing this. */ + mutex_lock(&lguest_lock); + down_read(fshared); + if (get_futex_key((u32 __user *)ukey, fshared, &key) != 0) { + kill_guest(lg, "bad dma key %#lx", ukey); + goto unlock; + } + + /* We want to keep this key valid once we drop mmap_sem, so we have to + * hold a reference. */ + get_futex_key_refs(&key); + + /* If the Guest specified an interrupt of 0, that means they want to + * unregister this array of "struct lguest_dma"s. */ + if (interrupt == 0) + ret = unbind_dma(lg, &key, dmas); + else { + /* Look through this Guest's dma array for an unused entry. */ + for (i = 0; i < LGUEST_MAX_DMA; i++) { + /* If the interrupt is non-zero, the entry is already + * used. */ + if (lg->dma[i].interrupt) + continue; + + /* OK, a free one! Fill on our details. */ + lg->dma[i].dmas = dmas; + lg->dma[i].num_dmas = numdmas; + lg->dma[i].next_dma = 0; + lg->dma[i].key = key; + lg->dma[i].guestid = lg->guestid; + lg->dma[i].interrupt = interrupt; + + /* Now we add it to the hash table: the position + * depends on the futex key that we got. */ + list_add(&lg->dma[i].list, &dma_hash[hash(&key)]); + /* Success! */ + ret = 1; + goto unlock; + } + } + /* If we didn't find a slot to put the key in, drop the reference + * again. */ + drop_futex_key_refs(&key); +unlock: + /* Unlock and out. */ + up_read(fshared); + mutex_unlock(&lguest_lock); + return ret; +} + +/*L:385 Note that our routines to access a different Guest's memory are called + * lgread_other() and lgwrite_other(): these names emphasize that they are only + * used when the Guest is *not* the current Guest. + * + * The interface for copying from another process's memory is called + * access_process_vm(), with a final argument of 0 for a read, and 1 for a + * write. + * + * We need lgread_other() to read the destination Guest's "struct lguest_dma" + * array. */ +static int lgread_other(struct lguest *lg, + void *buf, u32 addr, unsigned bytes) +{ + if (!lguest_address_ok(lg, addr, bytes) + || access_process_vm(lg->tsk, addr, buf, bytes, 0) != bytes) { + memset(buf, 0, bytes); + kill_guest(lg, "bad address in registered DMA struct"); + return 0; + } + return 1; +} + +/* "lgwrite()" to another Guest: used to update the destination "used_len" once + * we've transferred data into the buffer. */ +static int lgwrite_other(struct lguest *lg, u32 addr, + const void *buf, unsigned bytes) +{ + if (!lguest_address_ok(lg, addr, bytes) + || (access_process_vm(lg->tsk, addr, (void *)buf, bytes, 1) + != bytes)) { + kill_guest(lg, "bad address writing to registered DMA"); + return 0; + } + return 1; +} + +/*L:400 This is the generic engine which copies from a source "struct + * lguest_dma" from this Guest into another Guest's "struct lguest_dma". The + * destination Guest's pages have already been mapped, as contained in the + * pages array. + * + * If you're wondering if there's a nice "copy from one process to another" + * routine, so was I. But Linux isn't really set up to copy between two + * unrelated processes, so we have to write it ourselves. + */ +static u32 copy_data(struct lguest *srclg, + const struct lguest_dma *src, + const struct lguest_dma *dst, + struct page *pages[]) +{ + unsigned int totlen, si, di, srcoff, dstoff; + void *maddr = NULL; + + /* We return the total length transferred. */ + totlen = 0; + + /* We keep indexes into the source and destination "struct lguest_dma", + * and an offset within each region. */ + si = di = 0; + srcoff = dstoff = 0; + + /* We loop until the source or destination is exhausted. */ + while (si < LGUEST_MAX_DMA_SECTIONS && src->len[si] + && di < LGUEST_MAX_DMA_SECTIONS && dst->len[di]) { + /* We can only transfer the rest of the src buffer, or as much + * as will fit into the destination buffer. */ + u32 len = min(src->len[si] - srcoff, dst->len[di] - dstoff); + + /* For systems using "highmem" we need to use kmap() to access + * the page we want. We often use the same page over and over, + * so rather than kmap() it on every loop, we set the maddr + * pointer to NULL when we need to move to the next + * destination page. */ + if (!maddr) + maddr = kmap(pages[di]); + + /* Copy directly from (this Guest's) source address to the + * destination Guest's kmap()ed buffer. Note that maddr points + * to the start of the page: we need to add the offset of the + * destination address and offset within the buffer. */ + + /* FIXME: This is not completely portable. I looked at + * copy_to_user_page(), and some arch's seem to need special + * flushes. x86 is fine. */ + if (copy_from_user(maddr + (dst->addr[di] + dstoff)%PAGE_SIZE, + (void __user *)src->addr[si], len) != 0) { + /* If a copy failed, it's the source's fault. */ + kill_guest(srclg, "bad address in sending DMA"); + totlen = 0; + break; + } + + /* Increment the total and src & dst offsets */ + totlen += len; + srcoff += len; + dstoff += len; + + /* Presumably we reached the end of the src or dest buffers: */ + if (srcoff == src->len[si]) { + /* Move to the next buffer at offset 0 */ + si++; + srcoff = 0; + } + if (dstoff == dst->len[di]) { + /* We need to unmap that destination page and reset + * maddr ready for the next one. */ + kunmap(pages[di]); + maddr = NULL; + di++; + dstoff = 0; + } + } + + /* If we still had a page mapped at the end, unmap now. */ + if (maddr) + kunmap(pages[di]); + + return totlen; +} + +/*L:390 This is how we transfer a "struct lguest_dma" from the source Guest + * (the current Guest which called SEND_DMA) to another Guest. */ +static u32 do_dma(struct lguest *srclg, const struct lguest_dma *src, + struct lguest *dstlg, const struct lguest_dma *dst) +{ + int i; + u32 ret; + struct page *pages[LGUEST_MAX_DMA_SECTIONS]; + + /* We check that both source and destination "struct lguest_dma"s are + * within the bounds of the source and destination Guests */ + if (!check_dma_list(dstlg, dst) || !check_dma_list(srclg, src)) + return 0; + + /* We need to map the pages which correspond to each parts of + * destination buffer. */ + for (i = 0; i < LGUEST_MAX_DMA_SECTIONS; i++) { + if (dst->len[i] == 0) + break; + /* get_user_pages() is a complicated function, especially since + * we only want a single page. But it works, and returns the + * number of pages. Note that we're holding the destination's + * mmap_sem, as get_user_pages() requires. */ + if (get_user_pages(dstlg->tsk, dstlg->mm, + dst->addr[i], 1, 1, 1, pages+i, NULL) + != 1) { + /* This means the destination gave us a bogus buffer */ + kill_guest(dstlg, "Error mapping DMA pages"); + ret = 0; + goto drop_pages; + } + } + + /* Now copy the data until we run out of src or dst. */ + ret = copy_data(srclg, src, dst, pages); + +drop_pages: + while (--i >= 0) + put_page(pages[i]); + return ret; +} + +/*L:380 Transferring data from one Guest to another is not as simple as I'd + * like. We've found the "struct lguest_dma_info" bound to the same address as + * the send, we need to copy into it. + * + * This function returns true if the destination array was empty. */ +static int dma_transfer(struct lguest *srclg, + unsigned long udma, + struct lguest_dma_info *dst) +{ + struct lguest_dma dst_dma, src_dma; + struct lguest *dstlg; + u32 i, dma = 0; + + /* From the "struct lguest_dma_info" we found in the hash, grab the + * Guest. */ + dstlg = &lguests[dst->guestid]; + /* Read in the source "struct lguest_dma" handed to SEND_DMA. */ + lgread(srclg, &src_dma, udma, sizeof(src_dma)); + + /* We need the destination's mmap_sem, and we already hold the source's + * mmap_sem for the futex key lookup. Normally this would suggest that + * we could deadlock if the destination Guest was trying to send to + * this source Guest at the same time, which is another reason that all + * I/O is done under the big lguest_lock. */ + down_read(&dstlg->mm->mmap_sem); + + /* Look through the destination DMA array for an available buffer. */ + for (i = 0; i < dst->num_dmas; i++) { + /* We keep a "next_dma" pointer which often helps us avoid + * looking at lots of previously-filled entries. */ + dma = (dst->next_dma + i) % dst->num_dmas; + if (!lgread_other(dstlg, &dst_dma, + dst->dmas + dma * sizeof(struct lguest_dma), + sizeof(dst_dma))) { + goto fail; + } + if (!dst_dma.used_len) + break; + } + + /* If we found a buffer, we do the actual data copy. */ + if (i != dst->num_dmas) { + unsigned long used_lenp; + unsigned int ret; + + ret = do_dma(srclg, &src_dma, dstlg, &dst_dma); + /* Put used length in the source "struct lguest_dma"'s used_len + * field. It's a little tricky to figure out where that is, + * though. */ + lgwrite_u32(srclg, + udma+offsetof(struct lguest_dma, used_len), ret); + /* Tranferring 0 bytes is OK if the source buffer was empty. */ + if (ret == 0 && src_dma.len[0] != 0) + goto fail; + + /* The destination Guest might be running on a different CPU: + * we have to make sure that it will see the "used_len" field + * change to non-zero *after* it sees the data we copied into + * the buffer. Hence a write memory barrier. */ + wmb(); + /* Figuring out where the destination's used_len field for this + * "struct lguest_dma" in the array is also a little ugly. */ + used_lenp = dst->dmas + + dma * sizeof(struct lguest_dma) + + offsetof(struct lguest_dma, used_len); + lgwrite_other(dstlg, used_lenp, &ret, sizeof(ret)); + /* Move the cursor for next time. */ + dst->next_dma++; + } + up_read(&dstlg->mm->mmap_sem); + + /* We trigger the destination interrupt, even if the destination was + * empty and we didn't transfer anything: this gives them a chance to + * wake up and refill. */ + set_bit(dst->interrupt, dstlg->irqs_pending); + /* Wake up the destination process. */ + wake_up_process(dstlg->tsk); + /* If we passed the last "struct lguest_dma", the receive had no + * buffers left. */ + return i == dst->num_dmas; + +fail: + up_read(&dstlg->mm->mmap_sem); + return 0; +} + +/*L:370 This is the counter-side to the BIND_DMA hypercall; the SEND_DMA + * hypercall. We find out who's listening, and send to them. */ +void send_dma(struct lguest *lg, unsigned long ukey, unsigned long udma) +{ + union futex_key key; + int empty = 0; + struct rw_semaphore *fshared = ¤t->mm->mmap_sem; + +again: + mutex_lock(&lguest_lock); + down_read(fshared); + /* Get the futex key for the key the Guest gave us */ + if (get_futex_key((u32 __user *)ukey, fshared, &key) != 0) { + kill_guest(lg, "bad sending DMA key"); + goto unlock; + } + /* Since the key must be a multiple of 4, the futex key uses the lower + * bit of the "offset" field (which would always be 0) to indicate a + * mapping which is shared with other processes (ie. Guests). */ + if (key.shared.offset & 1) { + struct lguest_dma_info *i; + /* Look through the hash for other Guests. */ + list_for_each_entry(i, &dma_hash[hash(&key)], list) { + /* Don't send to ourselves. */ + if (i->guestid == lg->guestid) + continue; + if (!key_eq(&key, &i->key)) + continue; + + /* If dma_transfer() tells us the destination has no + * available buffers, we increment "empty". */ + empty += dma_transfer(lg, udma, i); + break; + } + /* If the destination is empty, we release our locks and + * give the destination Guest a brief chance to restock. */ + if (empty == 1) { + /* Give any recipients one chance to restock. */ + up_read(¤t->mm->mmap_sem); + mutex_unlock(&lguest_lock); + /* Next time, we won't try again. */ + empty++; + goto again; + } + } else { + /* Private mapping: Guest is sending to its Launcher. We set + * the "dma_is_pending" flag so that the main loop will exit + * and the Launcher's read() from /dev/lguest will return. */ + lg->dma_is_pending = 1; + lg->pending_dma = udma; + lg->pending_key = ukey; + } +unlock: + up_read(fshared); + mutex_unlock(&lguest_lock); +} +/*:*/ + +void release_all_dma(struct lguest *lg) +{ + unsigned int i; + + BUG_ON(!mutex_is_locked(&lguest_lock)); + + down_read(&lg->mm->mmap_sem); + for (i = 0; i < LGUEST_MAX_DMA; i++) { + if (lg->dma[i].interrupt) + unlink_dma(&lg->dma[i]); + } + up_read(&lg->mm->mmap_sem); +} + +/*M:007 We only return a single DMA buffer to the Launcher, but it would be + * more efficient to return a pointer to the entire array of DMA buffers, which + * it can cache and choose one whenever it wants. + * + * Currently the Launcher uses a write to /dev/lguest, and the return value is + * the address of the DMA structure with the interrupt number placed in + * dma->used_len. If we wanted to return the entire array, we need to return + * the address, array size and interrupt number: this seems to require an + * ioctl(). :*/ + +/*L:320 This routine looks for a DMA buffer registered by the Guest on the + * given key (using the BIND_DMA hypercall). */ +unsigned long get_dma_buffer(struct lguest *lg, + unsigned long ukey, unsigned long *interrupt) +{ + unsigned long ret = 0; + union futex_key key; + struct lguest_dma_info *i; + struct rw_semaphore *fshared = ¤t->mm->mmap_sem; + + /* Take the Big Lguest Lock to stop other Guests sending this Guest DMA + * at the same time. */ + mutex_lock(&lguest_lock); + /* To match between Guests sharing the same underlying memory we steal + * code from the futex infrastructure. This requires that we hold the + * "mmap_sem" for our process (the Launcher), and pass it to the futex + * code. */ + down_read(fshared); + + /* This can fail if it's not a valid address, or if the address is not + * divisible by 4 (the futex code needs that, we don't really). */ + if (get_futex_key((u32 __user *)ukey, fshared, &key) != 0) { + kill_guest(lg, "bad registered DMA buffer"); + goto unlock; + } + /* Search the hash table for matching entries (the Launcher can only + * send to its own Guest for the moment, so the entry must be for this + * Guest) */ + list_for_each_entry(i, &dma_hash[hash(&key)], list) { + if (key_eq(&key, &i->key) && i->guestid == lg->guestid) { + unsigned int j; + /* Look through the registered DMA array for an + * available buffer. */ + for (j = 0; j < i->num_dmas; j++) { + struct lguest_dma dma; + + ret = i->dmas + j * sizeof(struct lguest_dma); + lgread(lg, &dma, ret, sizeof(dma)); + if (dma.used_len == 0) + break; + } + /* Store the interrupt the Guest wants when the buffer + * is used. */ + *interrupt = i->interrupt; + break; + } + } +unlock: + up_read(fshared); + mutex_unlock(&lguest_lock); + return ret; +} +/*:*/ + +/*L:410 This really has completed the Launcher. Not only have we now finished + * the longest chapter in our journey, but this also means we are over halfway + * through! + * + * Enough prevaricating around the bush: it is time for us to dive into the + * core of the Host, in "make Host". + */ |
