Re: [PATCH] ummunotify: Userspace support for MMU notifications V2
From: Sayantan Sur
Date: Tue May 11 2010 - 12:17:35 EST
Hi,
I understand that this patch went through to the -mm tree.
MVAPICH/MVAPICH2 MPI stacks intend to utilize this feature as well.
Thanks.
On Thu, Apr 22, 2010 at 6:38 AM, Eric B Munson <ebmunson@xxxxxxxxxx> wrote:
> From: Roland Dreier <rolandd@xxxxxxxxx>
>
> As discussed in <http://article.gmane.org/gmane.linux.drivers.openib/61925>
> and follow-up messages, libraries using RDMA would like to track
> precisely when application code changes memory mapping via free(),
> munmap(), etc. Current pure-userspace solutions using malloc hooks
> and other tricks are not robust, and the feeling among experts is that
> the issue is unfixable without kernel help.
>
> We solve this not by implementing the full API proposed in the email
> linked above but rather with a simpler and more generic interface,
> which may be useful in other contexts. Specifically, we implement a
> new character device driver, ummunotify, that creates a /dev/ummunotify
> node. A userspace process can open this node read-only and use the fd
> as follows:
>
> 1. ioctl() to register/unregister an address range to watch in the
> kernel (cf struct ummunotify_register_ioctl in <linux/ummunotify.h>).
>
> 2. read() to retrieve events generated when a mapping in a watched
> address range is invalidated (cf struct ummunotify_event in
> <linux/ummunotify.h>). select()/poll()/epoll() and SIGIO are
> handled for this IO.
>
> 3. mmap() one page at offset 0 to map a kernel page that contains a
> generation counter that is incremented each time an event is
> generated. This allows userspace to have a fast path that checks
> that no events have occurred without a system call.
>
> Thanks to Jason Gunthorpe <jgunthorpe <at> obsidianresearch.com> for
> suggestions on the interface design. Also thanks to Jeff Squyres
> <jsquyres <at> cisco.com> for prototyping support for this in Open MPI,
> which
> helped find several bugs during development.
>
> Signed-off-by: Roland Dreier <rolandd@xxxxxxxxx>
> Signed-off-by: Eric B Munson <ebmunson@xxxxxxxxxx>
>
> ---
>
> Changes from V1:
> - Update Kbuild to handle test program build properly
> - Update documentation to cover questions not addressed in previous
> thread
> ---
> Documentation/Makefile | 3 +-
> Documentation/ummunotify/Makefile | 7 +
> Documentation/ummunotify/ummunotify.txt | 162 +++++++++
> Documentation/ummunotify/umn-test.c | 200 +++++++++++
> drivers/char/Kconfig | 12 +
> drivers/char/Makefile | 1 +
> drivers/char/ummunotify.c | 567
> +++++++++++++++++++++++++++++++
> include/linux/Kbuild | 1 +
> include/linux/ummunotify.h | 121 +++++++
> 9 files changed, 1073 insertions(+), 1 deletions(-)
> create mode 100644 Documentation/ummunotify/Makefile
> create mode 100644 Documentation/ummunotify/ummunotify.txt
> create mode 100644 Documentation/ummunotify/umn-test.c
> create mode 100644 drivers/char/ummunotify.c
> create mode 100644 include/linux/ummunotify.h
>
> diff --git a/Documentation/Makefile b/Documentation/Makefile
> index 6fc7ea1..27ba76a 100644
> --- a/Documentation/Makefile
> +++ b/Documentation/Makefile
> @@ -1,3 +1,4 @@
> obj-m := DocBook/ accounting/ auxdisplay/ connector/ \
> filesystems/ filesystems/configfs/ ia64/ laptops/ networking/ \
> - pcmcia/ spi/ timers/ video4linux/ vm/ watchdog/src/
> + pcmcia/ spi/ timers/ video4linux/ vm/ ummunotify/ \
> + watchdog/src/
> diff --git a/Documentation/ummunotify/Makefile
> b/Documentation/ummunotify/Makefile
> new file mode 100644
> index 0000000..89f31a0
> --- /dev/null
> +++ b/Documentation/ummunotify/Makefile
> @@ -0,0 +1,7 @@
> +# List of programs to build
> +hostprogs-y := umn-test
> +
> +# Tell kbuild to always build the programs
> +always := $(hostprogs-y)
> +
> +HOSTCFLAGS_umn-test.o += -I$(objtree)/usr/include
> diff --git a/Documentation/ummunotify/ummunotify.txt
> b/Documentation/ummunotify/ummunotify.txt
> new file mode 100644
> index 0000000..d6c2ccc
> --- /dev/null
> +++ b/Documentation/ummunotify/ummunotify.txt
> @@ -0,0 +1,162 @@
> +UMMUNOTIFY
> +
> + Ummunotify relays MMU notifier events to userspace. This is useful
> + for libraries that need to track the memory mapping of applications;
> + for example, MPI implementations using RDMA want to cache memory
> + registrations for performance, but tracking all possible crazy cases
> + such as when, say, the FORTRAN runtime frees memory is impossible
> + without kernel help.
> +
> +Basic Model
> +
> + A userspace process uses it by opening /dev/ummunotify, which
> + returns a file descriptor. Interest in address ranges is registered
> + using ioctl() and MMU notifier events are retrieved using read(), as
> + described in more detail below. Userspace can register multiple
> + address ranges to watch, and can unregister individual ranges.
> +
> + Userspace can also mmap() a single read-only page at offset 0 on
> + this file descriptor. This page contains (at offest 0) a single
> + 64-bit generation counter that the kernel increments each time an
> + MMU notifier event occurs. Userspace can use this to very quickly
> + check if there are any events to retrieve without needing to do a
> + system call.
> +
> +Control
> +
> + To start using ummunotify, a process opens /dev/ummunotify in
> + read-only mode. This will attach to current->mm because the current
> + consumers of this functionality do all monitoring in the process
> + being monitored. It is currently not possible to use this device to
> + monitor other processes. Control from userspace is done via ioctl().
> + An ioctl was chosen because the number of files required to register
> + a new address range in sysfs would be unwieldy and new procfs entries
> + are discouraged. The defined ioctls are:
> +
> + UMMUNOTIFY_EXCHANGE_FEATURES: This ioctl takes a single 32-bit
> + word of feature flags as input, and the kernel updates the
> + features flags word to contain only features requested by
> + userspace and also supported by the kernel.
> +
> + This ioctl is only included for forward compatibility; no
> + feature flags are currently defined, and the kernel will simply
> + update any requested feature mask to 0. The kernel will always
> + default to a feature mask of 0 if this ioctl is not used, so
> + current userspace does not need to perform this ioctl.
> +
> + UMMUNOTIFY_REGISTER_REGION: Userspace uses this ioctl to tell the
> + kernel to start delivering events for an address range. The
> + range is described using struct ummunotify_register_ioctl:
> +
> + struct ummunotify_register_ioctl {
> + __u64 start;
> + __u64 end;
> + __u64 user_cookie;
> + __u32 flags;
> + __u32 reserved;
> + };
> +
> + start and end give the range of userspace virtual addresses;
> + start is included in the range and end is not, so an example of
> + a 4 KB range would be start=0x1000, end=0x2000.
> +
> + user_cookie is an opaque 64-bit quantity that is returned by the
> + kernel in events involving the range, and used by userspace to
> + stop watching the range. Each registered address range must
> + have a distinct user_cookie.
> +
> + It is fine with the kernel if userspace registers multiple
> + overlapping or even duplicate address ranges, as long as a
> + different cookie is used for each registration.
> +
> + flags and reserved are included for forward compatibility;
> + userspace should simply set them to 0 for the current interface.
> +
> + UMMUNOTIFY_UNREGISTER_REGION: Userspace passes in the 64-bit
> + user_cookie used to register a range to tell the kernel to stop
> + watching an address range. Once this ioctl completes, the
> + kernel will not deliver any further events for the range that is
> + unregistered.
> +
> +Events
> +
> + When an event occurs that invalidates some of a process's memory
> + mapping in an address range being watched, ummunotify queues an
> + event report for that address range. If more than one event
> + invalidates parts of the same address range before userspace
> + retrieves the queued report, then further reports for the same range
> + will not be queued -- when userspace does read the queue, only a
> + single report for a given range will be returned.
> +
> + If multiple ranges being watched are invalidated by a single event
> + (which is especially likely if userspace registers overlapping
> + ranges), then an event report structure will be queued for each
> + address range registration.
> +
> + It is possible, if a large enough number of overlapping ranges are
> + registered and the list of invalidated events is busy enough and
> + ignored long enough, to cause the kernel to run out of memory.
> + Because this situation is unlikely to occur, the event queue size
> + is not bounded in order to avoid dropping events if the queue grows
> + beyond set bounds.
> +
> + Userspace retrieves queued events via read() on the ummunotify file
> + descriptor; a buffer that is at least as big as struct
> + ummunotify_event should be used to retrieve event reports, and if a
> + larger buffer is passed to read(), multiple reports will be returned
> + (if available).
> +
> + If the ummunotify file descriptor is in blocking mode, a read() call
> + will wait for an event report to be available. Userspace may also
> + set the ummunotify file descriptor to non-blocking mode and use all
> + standard ways of waiting for data to be available on the ummunotify
> + file descriptor, including epoll/poll()/select() and SIGIO.
> +
> + The format of event reports is:
> +
> + struct ummunotify_event {
> + __u32 type;
> + __u32 flags;
> + __u64 hint_start;
> + __u64 hint_end;
> + __u64 user_cookie_counter;
> + };
> +
> + where the type field is either UMMUNOTIFY_EVENT_TYPE_INVAL or
> + UMMUNOTIFY_EVENT_TYPE_LAST. Events of type INVAL describe
> + invalidation events as follows: user_cookie_counter contains the
> + cookie passed in when userspace registered the range that the event
> + is for. hint_start and hint_end contain the start address and end
> + address that were invalidated.
> +
> + The flags word contains bit flags, with only UMMUNOTIFY_EVENT_FLAG_HINT
> + defined at the moment. If HINT is set, then the invalidation event
> + invalidated less than the full address range and the kernel returns
> + the exact range invalidated; if HINT is not sent then hint_start and
> + hint_end are set to the original range registered by userspace.
> + (HINT will not be set if, for example, multiple events invalidated
> + disjoint parts of the range and so a single start/end pair cannot
> + represent the parts of the range that were invalidated)
> +
> + If the event type is LAST, then the read operation has emptied the
> + list of invalidated regions, and the flags, hint_start and hint_end
> + fields are not used. user_cookie_counter holds the value of the
> + kernel's generation counter (see below of more details) when the
> + empty list occurred.
> +
> +Generation Count
> +
> + Userspace may mmap() a page on a ummunotify file descriptor via
> +
> + mmap(NULL, sizeof (__u64), PROT_READ, MAP_SHARED, ummunotify_fd, 0);
> +
> + to get a read-only mapping of the kernel's 64-bit generation
> + counter. The kernel will increment this generation counter each
> + time an event report is queued.
> +
> + Userspace can use the generation counter as a quick check to avoid
> + system calls; if the value read from the mapped kernel counter is
> + still equal to the value returned in user_cookie_counter for the
> + most recent LAST event retrieved, then no further events have been
> + queued and there is no need to try a read() on the ummunotify file
> + descriptor.
> diff --git a/Documentation/ummunotify/umn-test.c
> b/Documentation/ummunotify/umn-test.c
> new file mode 100644
> index 0000000..143db2c
> --- /dev/null
> +++ b/Documentation/ummunotify/umn-test.c
> @@ -0,0 +1,200 @@
> +/*
> + * Copyright (c) 2009 Cisco Systems. All rights reserved.
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License version
> + * 2 as published by the Free Software Foundation.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
> + * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
> + * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
> + * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
> + * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
> + * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
> + * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
> + * SOFTWARE.
> + */
> +
> +#include <stdint.h>
> +#include <fcntl.h>
> +#include <stdio.h>
> +#include <unistd.h>
> +
> +#include <linux/ummunotify.h>
> +
> +#include <sys/mman.h>
> +#include <sys/stat.h>
> +#include <sys/types.h>
> +#include <sys/ioctl.h>
> +
> +#define UMN_TEST_COOKIE 123
> +
> +static int umn_fd;
> +static volatile __u64 *umn_counter;
> +
> +static int umn_init(void)
> +{
> + __u32 flags;
> +
> + umn_fd = open("/dev/ummunotify", O_RDONLY);
> + if (umn_fd < 0) {
> + perror("open");
> + return 1;
> + }
> +
> + if (ioctl(umn_fd, UMMUNOTIFY_EXCHANGE_FEATURES, &flags)) {
> + perror("exchange ioctl");
> + return 1;
> + }
> +
> + printf("kernel feature flags: 0x%08x\n", flags);
> +
> + umn_counter = mmap(NULL, sizeof *umn_counter, PROT_READ,
> + MAP_SHARED, umn_fd, 0);
> + if (umn_counter == MAP_FAILED) {
> + perror("mmap");
> + return 1;
> + }
> +
> + return 0;
> +}
> +
> +static int umn_register(void *buf, size_t size, __u64 cookie)
> +{
> + struct ummunotify_register_ioctl r = {
> + .start = (unsigned long) buf,
> + .end = (unsigned long) buf + size,
> + .user_cookie = cookie,
> + };
> +
> + if (ioctl(umn_fd, UMMUNOTIFY_REGISTER_REGION, &r)) {
> + perror("register ioctl");
> + return 1;
> + }
> +
> + return 0;
> +}
> +
> +static int umn_unregister(__u64 cookie)
> +{
> + if (ioctl(umn_fd, UMMUNOTIFY_UNREGISTER_REGION, &cookie)) {
> + perror("unregister ioctl");
> + return 1;
> + }
> +
> + return 0;
> +}
> +
> +int main(int argc, char *argv[])
> +{
> + int page_size;
> + __u64 old_counter;
> + void *t;
> + int got_it;
> +
> + if (umn_init())
> + return 1;
> +
> + printf("\n");
> +
> + old_counter = *umn_counter;
> + if (old_counter != 0) {
> + fprintf(stderr, "counter = %lld (expected 0)\n",
> old_counter);
> + return 1;
> + }
> +
> + page_size = sysconf(_SC_PAGESIZE);
> + t = mmap(NULL, 3 * page_size, PROT_READ,
> + MAP_PRIVATE | MAP_ANONYMOUS | MAP_POPULATE, -1, 0);
> +
> + if (umn_register(t, 3 * page_size, UMN_TEST_COOKIE))
> + return 1;
> +
> + munmap(t + page_size, page_size);
> +
> + old_counter = *umn_counter;
> + if (old_counter != 1) {
> + fprintf(stderr, "counter = %lld (expected 1)\n",
> old_counter);
> + return 1;
> + }
> +
> + got_it = 0;
> + while (1) {
> + struct ummunotify_event ev;
> + int len;
> +
> + len = read(umn_fd, &ev, sizeof ev);
> + if (len < 0) {
> + perror("read event");
> + return 1;
> + }
> + if (len != sizeof ev) {
> + fprintf(stderr, "Read gave %d bytes (!= event size
> %zd)\n",
> + len, sizeof ev);
> + return 1;
> + }
> +
> + switch (ev.type) {
> + case UMMUNOTIFY_EVENT_TYPE_INVAL:
> + if (got_it) {
> + fprintf(stderr, "Extra invalidate event\n");
> + return 1;
> + }
> + if (ev.user_cookie_counter != UMN_TEST_COOKIE) {
> + fprintf(stderr, "Invalidate event for cookie
> %lld (expected %d)\n",
> + ev.user_cookie_counter,
> + UMN_TEST_COOKIE);
> + return 1;
> + }
> +
> + printf("Invalidate event:\tcookie %lld\n",
> + ev.user_cookie_counter);
> +
> + if (!(ev.flags & UMMUNOTIFY_EVENT_FLAG_HINT)) {
> + fprintf(stderr, "Hint flag not set\n");
> + return 1;
> + }
> +
> + if (ev.hint_start != (uintptr_t) t + page_size ||
> + ev.hint_end != (uintptr_t) t + page_size * 2) {
> + fprintf(stderr, "Got hint %llx..%llx,
> expected %p..%p\n",
> + ev.hint_start, ev.hint_end,
> + t + page_size, t + page_size * 2);
> + return 1;
> + }
> +
> + printf("\t\t\thint %llx...%llx\n",
> + ev.hint_start, ev.hint_end);
> +
> + got_it = 1;
> + break;
> +
> + case UMMUNOTIFY_EVENT_TYPE_LAST:
> + if (!got_it) {
> + fprintf(stderr, "Last event without
> invalidate event\n");
> + return 1;
> + }
> +
> + printf("Empty event:\t\tcounter %lld\n",
> + ev.user_cookie_counter);
> + goto done;
> +
> + default:
> + fprintf(stderr, "unknown event type %d\n",
> + ev.type);
> + return 1;
> + }
> + }
> +
> +done:
> + umn_unregister(123);
> + munmap(t, page_size);
> +
> + old_counter = *umn_counter;
> + if (old_counter != 1) {
> + fprintf(stderr, "counter = %lld (expected 1)\n",
> old_counter);
> + return 1;
> + }
> +
> + return 0;
> +}
> diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
> index 3141dd3..cf26019 100644
> --- a/drivers/char/Kconfig
> +++ b/drivers/char/Kconfig
> @@ -1111,6 +1111,18 @@ config DEVPORT
> depends on ISA || PCI
> default y
>
> +config UMMUNOTIFY
> + tristate "Userspace MMU notifications"
> + select MMU_NOTIFIER
> + help
> + The ummunotify (userspace MMU notification) driver creates a
> + character device that can be used by userspace libraries to
> + get notifications when an application's memory mapping
> + changed. This is used, for example, by RDMA libraries to
> + improve the reliability of memory registration caching, since
> + the kernel's MMU notifications can be used to know precisely
> + when to shoot down a cached registration.
> +
> source "drivers/s390/char/Kconfig"
>
> endmenu
> diff --git a/drivers/char/Makefile b/drivers/char/Makefile
> index f957edf..521e5de 100644
> --- a/drivers/char/Makefile
> +++ b/drivers/char/Makefile
> @@ -97,6 +97,7 @@ obj-$(CONFIG_NSC_GPIO) += nsc_gpio.o
> obj-$(CONFIG_CS5535_GPIO) += cs5535_gpio.o
> obj-$(CONFIG_GPIO_TB0219) += tb0219.o
> obj-$(CONFIG_TELCLOCK) += tlclk.o
> +obj-$(CONFIG_UMMUNOTIFY) += ummunotify.o
>
> obj-$(CONFIG_MWAVE) += mwave/
> obj-$(CONFIG_AGP) += agp/
> diff --git a/drivers/char/ummunotify.c b/drivers/char/ummunotify.c
> new file mode 100644
> index 0000000..c14df3f
> --- /dev/null
> +++ b/drivers/char/ummunotify.c
> @@ -0,0 +1,567 @@
> +/*
> + * Copyright (c) 2009 Cisco Systems. All rights reserved.
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License version
> + * 2 as published by the Free Software Foundation.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
> + * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
> + * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
> + * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
> + * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
> + * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
> + * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
> + * SOFTWARE.
> + */
> +
> +#include <linux/fs.h>
> +#include <linux/init.h>
> +#include <linux/list.h>
> +#include <linux/miscdevice.h>
> +#include <linux/mm.h>
> +#include <linux/mmu_notifier.h>
> +#include <linux/module.h>
> +#include <linux/poll.h>
> +#include <linux/rbtree.h>
> +#include <linux/sched.h>
> +#include <linux/slab.h>
> +#include <linux/spinlock.h>
> +#include <linux/uaccess.h>
> +#include <linux/ummunotify.h>
> +
> +#include <asm/cacheflush.h>
> +
> +MODULE_AUTHOR("Roland Dreier");
> +MODULE_DESCRIPTION("Userspace MMU notifiers");
> +MODULE_LICENSE("GPL v2");
> +
> +/*
> + * Information about an address range userspace has asked us to watch.
> + *
> + * user_cookie: Opaque cookie given to us when userspace registers the
> + * address range.
> + *
> + * start, end: Address range; start is inclusive, end is exclusive.
> + *
> + * hint_start, hint_end: If a single MMU notification event
> + * invalidates the address range, we hold the actual range of
> + * addresses that were invalidated (and set UMMUNOTIFY_FLAG_HINT).
> + * If another event hits this range before userspace reads the
> + * event, we give up and don't try to keep track of which subsets
> + * got invalidated.
> + *
> + * flags: Holds the INVALID flag for ranges that are on the invalid
> + * list and/or the HINT flag for ranges where the hint range holds
> + * good information.
> + *
> + * node: Used to put the range into an rbtree we use to be able to
> + * scan address ranges in order.
> + *
> + * list: Used to put the range on the invalid list when an MMU
> + * notification event hits the range.
> + */
> +enum {
> + UMMUNOTIFY_FLAG_INVALID = 1,
> + UMMUNOTIFY_FLAG_HINT = 2,
> +};
> +
> +struct ummunotify_reg {
> + u64 user_cookie;
> + unsigned long start;
> + unsigned long end;
> + unsigned long hint_start;
> + unsigned long hint_end;
> + unsigned long flags;
> + struct rb_node node;
> + struct list_head list;
> +};
> +
> +/*
> + * Context attached to each file that userspace opens.
> + *
> + * mmu_notifier: MMU notifier registered for this context.
> + *
> + * mm: mm_struct for process that created the context; we use this to
> + * hold a reference to the mm to make sure it doesn't go away until
> + * we're done with it.
> + *
> + * reg_tree: RB tree of address ranges being watched, sorted by start
> + * address.
> + *
> + * invalid_list: List of address ranges that have been invalidated by
> + * MMU notification events; as userspace reads events, the address
> + * range corresponding to the event is removed from the list.
> + *
> + * counter: Page that can be mapped read-only by userspace, which
> + * holds a generation count that is incremented each time an event
> + * occurs.
> + *
> + * lock: Spinlock used to protect all context.
> + *
> + * read_wait: Wait queue used to wait for data to become available in
> + * blocking read()s.
> + *
> + * async_queue: Used to implement fasync().
> + *
> + * need_empty: Set when userspace reads an invalidation event, so that
> + * read() knows it must generate an "empty" event when userspace
> + * drains the invalid_list.
> + *
> + * used: Set after userspace does anything with the file, so that the
> + * "exchange flags" ioctl() knows it's too late to change anything.
> + */
> +struct ummunotify_file {
> + struct mmu_notifier mmu_notifier;
> + struct mm_struct *mm;
> + struct rb_root reg_tree;
> + struct list_head invalid_list;
> + u64 *counter;
> + spinlock_t lock;
> + wait_queue_head_t read_wait;
> + struct fasync_struct *async_queue;
> + int need_empty;
> + int used;
> +};
> +
> +static void ummunotify_handle_notify(struct mmu_notifier *mn,
> + unsigned long start, unsigned long end)
> +{
> + struct ummunotify_file *priv =
> + container_of(mn, struct ummunotify_file, mmu_notifier);
> + struct rb_node *n;
> + struct ummunotify_reg *reg;
> + unsigned long flags;
> + int hit = 0;
> +
> + spin_lock_irqsave(&priv->lock, flags);
> +
> + for (n = rb_first(&priv->reg_tree); n; n = rb_next(n)) {
> + reg = rb_entry(n, struct ummunotify_reg, node);
> +
> + /*
> + * Ranges overlap if they're not disjoint; and they're
> + * disjoint if the end of one is before the start of
> + * the other one. So if both disjointness comparisons
> + * fail then the ranges overlap.
> + *
> + * Since we keep the tree of regions we're watching
> + * sorted by start address, we can end this loop as
> + * soon as we hit a region that starts past the end of
> + * the range for the event we're handling.
> + */
> + if (reg->start >= end)
> + break;
> +
> + /*
> + * Just go to the next region if the start of the
> + * range is after the end of the region -- there
> + * might still be more overlapping ranges that have a
> + * greater start.
> + */
> + if (start >= reg->end)
> + continue;
> +
> + hit = 1;
> +
> + if (test_and_set_bit(UMMUNOTIFY_FLAG_INVALID, ®->flags))
> {
> + /* Already on invalid list */
> + clear_bit(UMMUNOTIFY_FLAG_HINT, ®->flags);
> + } else {
> + list_add_tail(®->list, &priv->invalid_list);
> + set_bit(UMMUNOTIFY_FLAG_HINT, ®->flags);
> + reg->hint_start = start;
> + reg->hint_end = end;
> + }
> + }
> +
> + if (hit) {
> + ++(*priv->counter);
> + flush_dcache_page(virt_to_page(priv->counter));
> + wake_up_interruptible(&priv->read_wait);
> + kill_fasync(&priv->async_queue, SIGIO, POLL_IN);
> + }
> +
> + spin_unlock_irqrestore(&priv->lock, flags);
> +}
> +
> +static void ummunotify_invalidate_page(struct mmu_notifier *mn,
> + struct mm_struct *mm,
> + unsigned long addr)
> +{
> + ummunotify_handle_notify(mn, addr, addr + PAGE_SIZE);
> +}
> +
> +static void ummunotify_invalidate_range_start(struct mmu_notifier *mn,
> + struct mm_struct *mm,
> + unsigned long start,
> + unsigned long end)
> +{
> + ummunotify_handle_notify(mn, start, end);
> +}
> +
> +static const struct mmu_notifier_ops ummunotify_mmu_notifier_ops = {
> + .invalidate_page = ummunotify_invalidate_page,
> + .invalidate_range_start = ummunotify_invalidate_range_start,
> +};
> +
> +static int ummunotify_open(struct inode *inode, struct file *filp)
> +{
> + struct ummunotify_file *priv;
> + int ret;
> +
> + if (filp->f_mode & FMODE_WRITE)
> + return -EINVAL;
> +
> + priv = kmalloc(sizeof *priv, GFP_KERNEL);
> + if (!priv)
> + return -ENOMEM;
> +
> + priv->counter = (void *) get_zeroed_page(GFP_KERNEL);
> + if (!priv->counter) {
> + ret = -ENOMEM;
> + goto err;
> + }
> +
> + priv->reg_tree = RB_ROOT;
> + INIT_LIST_HEAD(&priv->invalid_list);
> + spin_lock_init(&priv->lock);
> + init_waitqueue_head(&priv->read_wait);
> + priv->async_queue = NULL;
> + priv->need_empty = 0;
> + priv->used = 0;
> +
> + priv->mmu_notifier.ops = &ummunotify_mmu_notifier_ops;
> + /*
> + * Register notifier last, since notifications can occur as
> + * soon as we register....
> + */
> + ret = mmu_notifier_register(&priv->mmu_notifier, current->mm);
> + if (ret)
> + goto err_page;
> +
> + priv->mm = current->mm;
> + atomic_inc(&priv->mm->mm_count);
> +
> + filp->private_data = priv;
> +
> + return 0;
> +
> +err_page:
> + free_page((unsigned long) priv->counter);
> +
> +err:
> + kfree(priv);
> + return ret;
> +}
> +
> +static int ummunotify_close(struct inode *inode, struct file *filp)
> +{
> + struct ummunotify_file *priv = filp->private_data;
> + struct rb_node *n;
> + struct ummunotify_reg *reg;
> +
> + mmu_notifier_unregister(&priv->mmu_notifier, priv->mm);
> + mmdrop(priv->mm);
> + free_page((unsigned long) priv->counter);
> +
> + for (n = rb_first(&priv->reg_tree); n; n = rb_next(n)) {
> + reg = rb_entry(n, struct ummunotify_reg, node);
> + kfree(reg);
> + }
> +
> + kfree(priv);
> +
> + return 0;
> +}
> +
> +static bool ummunotify_readable(struct ummunotify_file *priv)
> +{
> + return priv->need_empty || !list_empty(&priv->invalid_list);
> +}
> +
> +static ssize_t ummunotify_read(struct file *filp, char __user *buf,
> + size_t count, loff_t *pos)
> +{
> + struct ummunotify_file *priv = filp->private_data;
> + struct ummunotify_reg *reg;
> + ssize_t ret;
> + struct ummunotify_event *events;
> + int max;
> + int n;
> +
> + priv->used = 1;
> +
> + events = (void *) get_zeroed_page(GFP_KERNEL);
> + if (!events) {
> + ret = -ENOMEM;
> + goto out;
> + }
> +
> + spin_lock_irq(&priv->lock);
> +
> + while (!ummunotify_readable(priv)) {
> + spin_unlock_irq(&priv->lock);
> +
> + if (filp->f_flags & O_NONBLOCK) {
> + ret = -EAGAIN;
> + goto out;
> + }
> +
> + if (wait_event_interruptible(priv->read_wait,
> + ummunotify_readable(priv))) {
> + ret = -ERESTARTSYS;
> + goto out;
> + }
> +
> + spin_lock_irq(&priv->lock);
> + }
> +
> + max = min_t(size_t, PAGE_SIZE, count) / sizeof *events;
> +
> + for (n = 0; n < max; ++n) {
> + if (list_empty(&priv->invalid_list)) {
> + events[n].type = UMMUNOTIFY_EVENT_TYPE_LAST;
> + events[n].user_cookie_counter = *priv->counter;
> + ++n;
> + priv->need_empty = 0;
> + break;
> + }
> +
> + reg = list_first_entry(&priv->invalid_list,
> + struct ummunotify_reg, list);
> +
> + events[n].type = UMMUNOTIFY_EVENT_TYPE_INVAL;
> + if (test_bit(UMMUNOTIFY_FLAG_HINT, ®->flags)) {
> + events[n].flags = UMMUNOTIFY_EVENT_FLAG_HINT;
> + events[n].hint_start = max(reg->start,
> reg->hint_start);
> + events[n].hint_end = min(reg->end, reg->hint_end);
> + } else {
> + events[n].hint_start = reg->start;
> + events[n].hint_end = reg->end;
> + }
> + events[n].user_cookie_counter = reg->user_cookie;
> +
> + list_del(®->list);
> + reg->flags = 0;
> + priv->need_empty = 1;
> + }
> +
> + spin_unlock_irq(&priv->lock);
> +
> + if (copy_to_user(buf, events, n * sizeof *events))
> + ret = -EFAULT;
> + else
> + ret = n * sizeof *events;
> +
> +out:
> + free_page((unsigned long) events);
> + return ret;
> +}
> +
> +static unsigned int ummunotify_poll(struct file *filp,
> + struct poll_table_struct *wait)
> +{
> + struct ummunotify_file *priv = filp->private_data;
> +
> + poll_wait(filp, &priv->read_wait, wait);
> +
> + return ummunotify_readable(priv) ? (POLLIN | POLLRDNORM) : 0;
> +}
> +
> +static long ummunotify_exchange_features(struct ummunotify_file *priv,
> + __u32 __user *arg)
> +{
> + u32 feature_mask;
> +
> + if (priv->used)
> + return -EINVAL;
> +
> + priv->used = 1;
> +
> + if (copy_from_user(&feature_mask, arg, sizeof(feature_mask)))
> + return -EFAULT;
> +
> + /* No extensions defined at present. */
> + feature_mask = 0;
> +
> + if (copy_to_user(arg, &feature_mask, sizeof(feature_mask)))
> + return -EFAULT;
> +
> + return 0;
> +}
> +
> +static long ummunotify_register_region(struct ummunotify_file *priv,
> + void __user *arg)
> +{
> + struct ummunotify_register_ioctl parm;
> + struct ummunotify_reg *reg, *treg;
> + struct rb_node **n = &priv->reg_tree.rb_node;
> + struct rb_node *pn;
> + int ret = 0;
> +
> + if (copy_from_user(&parm, arg, sizeof parm))
> + return -EFAULT;
> +
> + priv->used = 1;
> +
> + reg = kmalloc(sizeof *reg, GFP_KERNEL);
> + if (!reg)
> + return -ENOMEM;
> +
> + reg->user_cookie = parm.user_cookie;
> + reg->start = parm.start;
> + reg->end = parm.end;
> + reg->flags = 0;
> +
> + spin_lock_irq(&priv->lock);
> +
> + for (pn = rb_first(&priv->reg_tree); pn; pn = rb_next(pn)) {
> + treg = rb_entry(pn, struct ummunotify_reg, node);
> +
> + if (treg->user_cookie == parm.user_cookie) {
> + kfree(reg);
> + ret = -EINVAL;
> + goto out;
> + }
> + }
> +
> + pn = NULL;
> + while (*n) {
> + pn = *n;
> + treg = rb_entry(pn, struct ummunotify_reg, node);
> +
> + if (reg->start <= treg->start)
> + n = &pn->rb_left;
> + else
> + n = &pn->rb_right;
> + }
> +
> + rb_link_node(®->node, pn, n);
> + rb_insert_color(®->node, &priv->reg_tree);
> +
> +out:
> + spin_unlock_irq(&priv->lock);
> +
> + return ret;
> +}
> +
> +static long ummunotify_unregister_region(struct ummunotify_file *priv,
> + __u64 __user *arg)
> +{
> + u64 user_cookie;
> + struct rb_node *n;
> + struct ummunotify_reg *reg;
> + int ret = -EINVAL;
> +
> + if (copy_from_user(&user_cookie, arg, sizeof(user_cookie)))
> + return -EFAULT;
> +
> + spin_lock_irq(&priv->lock);
> +
> + for (n = rb_first(&priv->reg_tree); n; n = rb_next(n)) {
> + reg = rb_entry(n, struct ummunotify_reg, node);
> +
> + if (reg->user_cookie == user_cookie) {
> + rb_erase(n, &priv->reg_tree);
> + if (test_bit(UMMUNOTIFY_FLAG_INVALID, ®->flags))
> + list_del(®->list);
> + kfree(reg);
> + ret = 0;
> + break;
> + }
> + }
> +
> + spin_unlock_irq(&priv->lock);
> +
> + return ret;
> +}
> +
> +static long ummunotify_ioctl(struct file *filp, unsigned int cmd,
> + unsigned long arg)
> +{
> + struct ummunotify_file *priv = filp->private_data;
> + void __user *argp = (void __user *) arg;
> +
> + switch (cmd) {
> + case UMMUNOTIFY_EXCHANGE_FEATURES:
> + return ummunotify_exchange_features(priv, argp);
> + case UMMUNOTIFY_REGISTER_REGION:
> + return ummunotify_register_region(priv, argp);
> + case UMMUNOTIFY_UNREGISTER_REGION:
> + return ummunotify_unregister_region(priv, argp);
> + default:
> + return -ENOIOCTLCMD;
> + }
> +}
> +
> +static int ummunotify_fault(struct vm_area_struct *vma, struct vm_fault
> *vmf)
> +{
> + struct ummunotify_file *priv = vma->vm_private_data;
> +
> + if (vmf->pgoff != 0)
> + return VM_FAULT_SIGBUS;
> +
> + vmf->page = virt_to_page(priv->counter);
> + get_page(vmf->page);
> +
> + return 0;
> +
> +}
> +
> +static struct vm_operations_struct ummunotify_vm_ops = {
> + .fault = ummunotify_fault,
> +};
> +
> +static int ummunotify_mmap(struct file *filp, struct vm_area_struct *vma)
> +{
> + struct ummunotify_file *priv = filp->private_data;
> +
> + if (vma->vm_end - vma->vm_start != PAGE_SIZE || vma->vm_pgoff != 0)
> + return -EINVAL;
> +
> + vma->vm_ops = &ummunotify_vm_ops;
> + vma->vm_private_data = priv;
> +
> + return 0;
> +}
> +
> +static int ummunotify_fasync(int fd, struct file *filp, int on)
> +{
> + struct ummunotify_file *priv = filp->private_data;
> +
> + return fasync_helper(fd, filp, on, &priv->async_queue);
> +}
> +
> +static const struct file_operations ummunotify_fops = {
> + .owner = THIS_MODULE,
> + .open = ummunotify_open,
> + .release = ummunotify_close,
> + .read = ummunotify_read,
> + .poll = ummunotify_poll,
> + .unlocked_ioctl = ummunotify_ioctl,
> +#ifdef CONFIG_COMPAT
> + .compat_ioctl = ummunotify_ioctl,
> +#endif
> + .mmap = ummunotify_mmap,
> + .fasync = ummunotify_fasync,
> +};
> +
> +static struct miscdevice ummunotify_misc = {
> + .minor = MISC_DYNAMIC_MINOR,
> + .name = "ummunotify",
> + .fops = &ummunotify_fops,
> +};
> +
> +static int __init ummunotify_init(void)
> +{
> + return misc_register(&ummunotify_misc);
> +}
> +
> +static void __exit ummunotify_cleanup(void)
> +{
> + misc_deregister(&ummunotify_misc);
> +}
> +
> +module_init(ummunotify_init);
> +module_exit(ummunotify_cleanup);
> diff --git a/include/linux/Kbuild b/include/linux/Kbuild
> index e2ea0b2..e086b39 100644
> --- a/include/linux/Kbuild
> +++ b/include/linux/Kbuild
> @@ -163,6 +163,7 @@ header-y += tipc_config.h
> header-y += toshiba.h
> header-y += udf_fs_i.h
> header-y += ultrasound.h
> +header-y += ummunotify.h
> header-y += un.h
> header-y += utime.h
> header-y += veth.h
> diff --git a/include/linux/ummunotify.h b/include/linux/ummunotify.h
> new file mode 100644
> index 0000000..21b0d03
> --- /dev/null
> +++ b/include/linux/ummunotify.h
> @@ -0,0 +1,121 @@
> +/*
> + * Copyright (c) 2009 Cisco Systems. All rights reserved.
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License version
> + * 2 as published by the Free Software Foundation.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
> + * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
> + * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
> + * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
> + * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
> + * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
> + * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
> + * SOFTWARE.
> + */
> +
> +#ifndef _LINUX_UMMUNOTIFY_H
> +#define _LINUX_UMMUNOTIFY_H
> +
> +#include <linux/types.h>
> +#include <linux/ioctl.h>
> +
> +/*
> + * Ummunotify relays MMU notifier events to userspace. A userspace
> + * process uses it by opening /dev/ummunotify, which returns a file
> + * descriptor. Interest in address ranges is registered using ioctl()
> + * and MMU notifier events are retrieved using read(), as described in
> + * more detail below.
> + *
> + * Userspace can also mmap() a single read-only page at offset 0 on
> + * this file descriptor. This page contains (at offest 0) a single
> + * 64-bit generation counter that the kernel increments each time an
> + * MMU notifier event occurs. Userspace can use this to very quickly
> + * check if there are any events to retrieve without needing to do a
> + * system call.
> + */
> +
> +/*
> + * struct ummunotify_register_ioctl describes an address range from
> + * start to end (including start but not including end) to be
> + * monitored. user_cookie is an opaque handle that userspace assigns,
> + * and which is used to unregister. flags and reserved are currently
> + * unused and should be set to 0 for forward compatibility.
> + */
> +struct ummunotify_register_ioctl {
> + __u64 start;
> + __u64 end;
> + __u64 user_cookie;
> + __u32 flags;
> + __u32 reserved;
> +};
> +
> +#define UMMUNOTIFY_MAGIC 'U'
> +
> +/*
> + * Forward compatibility: Userspace passes in a 32-bit feature mask
> + * with feature flags set indicating which extensions it wishes to
> + * use. The kernel will return a feature mask with the bits of
> + * userspace's mask that the kernel implements; from that point on
> + * both userspace and the kernel should behave as described by the
> + * kernel's feature mask.
> + *
> + * If userspace does not perform a UMMUNOTIFY_EXCHANGE_FEATURES ioctl,
> + * then the kernel will use a feature mask of 0.
> + *
> + * No feature flags are currently defined, so the kernel will always
> + * return a feature mask of 0 at present.
> + */
> +#define UMMUNOTIFY_EXCHANGE_FEATURES _IOWR(UMMUNOTIFY_MAGIC, 1, __u32)
> +
> +/*
> + * Register interest in an address range; userspace should pass in a
> + * struct ummunotify_register_ioctl describing the region.
> + */
> +#define UMMUNOTIFY_REGISTER_REGION _IOW(UMMUNOTIFY_MAGIC, 2, \
> + struct
> ummunotify_register_ioctl)
> +/*
> + * Unregister interest in an address range; userspace should pass in
> + * the user_cookie value that was used to register the address range.
> + * No events for the address range will be reported once it is
> + * unregistered.
> + */
> +#define UMMUNOTIFY_UNREGISTER_REGION _IOW(UMMUNOTIFY_MAGIC, 3, __u64)
> +
> +/*
> + * Invalidation events are returned whenever the kernel changes the
> + * mapping for a monitored address. These events are retrieved by
> + * read() on the ummunotify file descriptor, which will fill the
> + * read() buffer with struct ummunotify_event.
> + *
> + * If type field is INVAL, then user_cookie_counter holds the
> + * user_cookie for the region being reported; if the HINT flag is set
> + * then hint_start/hint_end hold the start and end of the mapping that
> + * was invalidated. (If HINT is not set, then multiple events
> + * invalidated parts of the registered range and hint_start/hint_end
> + * and set to the start/end of the whole registered range)
> + *
> + * If type is LAST, then the read operation has emptied the list of
> + * invalidated regions, and user_cookie_counter holds the value of the
> + * kernel's generation counter when the empty list occurred. The
> + * other fields are not filled in for this event.
> + */
> +enum {
> + UMMUNOTIFY_EVENT_TYPE_INVAL = 0,
> + UMMUNOTIFY_EVENT_TYPE_LAST = 1,
> +};
> +
> +enum {
> + UMMUNOTIFY_EVENT_FLAG_HINT = 1 << 0,
> +};
> +
> +struct ummunotify_event {
> + __u32 type;
> + __u32 flags;
> + __u64 hint_start;
> + __u64 hint_end;
> + __u64 user_cookie_counter;
> +};
> +
> +#endif /* _LINUX_UMMUNOTIFY_H */
> --
> 1.6.3.3
>
>
--
Sayantan Sur
Research Scientist
Department of Computer Science
The Ohio State University.
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