+++ /dev/null
-/*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(lg->mem_base + 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].owner = lg;
- 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, (unsigned long)lg->mem_base + 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, (unsigned long)lg->mem_base + 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,
- srclg->mem_base+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,
- (unsigned long)dstlg->mem_base+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 = dst->owner;
- /* 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(lg->mem_base + 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 (would deadlock). */
- if (i->owner->mm == lg->mm)
- 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(lg->mem_base + 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->owner == lg) {
- 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".
- */
projects / linux-2.6 / commitdiff