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userfaultfd: non-cooperative: add ability to report non-PF events from uffd descriptor

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The custom events are queued in ctx->event_wqh not to disturb the
fast-path-ed PF queue-wait-wakeup functions.

The events to be generated (other than PF-s) are requested in UFFD_API
ioctl with the uffd_api.features bits. Those, known by the kernel, are
then turned on and reported back to the user-space.

Link: http://lkml.kernel.org/r/20161216144821.5183-7-aarcange@redhat.com
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Michael Rapoport <RAPOPORT@il.ibm.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Pavel Emelyanov 2017-02-22 15:42:21 -08:00 committed by Linus Torvalds
parent 6dcc27fd39
commit 9cd75c3cd4
1 changed files with 96 additions and 2 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

98
fs/userfaultfd.c
View file

@ -12,6 +12,7 @@
* mm/ksm.c (mm hashing).
*/
#include <linux/list.h>
#include <linux/hashtable.h>
#include <linux/sched.h>
#include <linux/mm.h>
@ -45,12 +46,16 @@ struct userfaultfd_ctx {
wait_queue_head_t fault_wqh;
/* waitqueue head for the pseudo fd to wakeup poll/read */
wait_queue_head_t fd_wqh;
/* waitqueue head for events */
wait_queue_head_t event_wqh;
/* a refile sequence protected by fault_pending_wqh lock */
struct seqcount refile_seq;
/* pseudo fd refcounting */
atomic_t refcount;
/* userfaultfd syscall flags */
unsigned int flags;
/* features requested from the userspace */
unsigned int features;
/* state machine */
enum userfaultfd_state state;
/* released */
@ -142,6 +147,8 @@ static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx)
VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh));
VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock));
VM_BUG_ON(waitqueue_active(&ctx->fault_wqh));
VM_BUG_ON(spin_is_locked(&ctx->event_wqh.lock));
VM_BUG_ON(waitqueue_active(&ctx->event_wqh));
VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock));
VM_BUG_ON(waitqueue_active(&ctx->fd_wqh));
mmdrop(ctx->mm);
@ -458,6 +465,59 @@ int handle_userfault(struct vm_fault *vmf, unsigned long reason)
return ret;
}
static int __maybe_unused userfaultfd_event_wait_completion(
struct userfaultfd_ctx *ctx,
struct userfaultfd_wait_queue *ewq)
{
int ret = 0;
ewq->ctx = ctx;
init_waitqueue_entry(&ewq->wq, current);
spin_lock(&ctx->event_wqh.lock);
/*
* After the __add_wait_queue the uwq is visible to userland
* through poll/read().
*/
__add_wait_queue(&ctx->event_wqh, &ewq->wq);
for (;;) {
set_current_state(TASK_KILLABLE);
if (ewq->msg.event == 0)
break;
if (ACCESS_ONCE(ctx->released) ||
fatal_signal_pending(current)) {
ret = -1;
__remove_wait_queue(&ctx->event_wqh, &ewq->wq);
break;
}
spin_unlock(&ctx->event_wqh.lock);
wake_up_poll(&ctx->fd_wqh, POLLIN);
schedule();
spin_lock(&ctx->event_wqh.lock);
}
__set_current_state(TASK_RUNNING);
spin_unlock(&ctx->event_wqh.lock);
/*
* ctx may go away after this if the userfault pseudo fd is
* already released.
*/
userfaultfd_ctx_put(ctx);
return ret;
}
static void userfaultfd_event_complete(struct userfaultfd_ctx *ctx,
struct userfaultfd_wait_queue *ewq)
{
ewq->msg.event = 0;
wake_up_locked(&ctx->event_wqh);
__remove_wait_queue(&ctx->event_wqh, &ewq->wq);
}
static int userfaultfd_release(struct inode *inode, struct file *file)
{
struct userfaultfd_ctx *ctx = file->private_data;
@ -546,6 +606,12 @@ static inline struct userfaultfd_wait_queue *find_userfault(
return find_userfault_in(&ctx->fault_pending_wqh);
}
static inline struct userfaultfd_wait_queue *find_userfault_evt(
struct userfaultfd_ctx *ctx)
{
return find_userfault_in(&ctx->event_wqh);
}
static unsigned int userfaultfd_poll(struct file *file, poll_table *wait)
{
struct userfaultfd_ctx *ctx = file->private_data;
@ -577,6 +643,9 @@ static unsigned int userfaultfd_poll(struct file *file, poll_table *wait)
smp_mb();
if (waitqueue_active(&ctx->fault_pending_wqh))
ret = POLLIN;
else if (waitqueue_active(&ctx->event_wqh))
ret = POLLIN;
return ret;
default:
WARN_ON_ONCE(1);
@ -641,6 +710,19 @@ static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
break;
}
spin_unlock(&ctx->fault_pending_wqh.lock);
spin_lock(&ctx->event_wqh.lock);
uwq = find_userfault_evt(ctx);
if (uwq) {
*msg = uwq->msg;
userfaultfd_event_complete(ctx, uwq);
spin_unlock(&ctx->event_wqh.lock);
ret = 0;
break;
}
spin_unlock(&ctx->event_wqh.lock);
if (signal_pending(current)) {
ret = -ERESTARTSYS;
break;
@ -1184,6 +1266,14 @@ static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
return ret;
}
static inline unsigned int uffd_ctx_features(__u64 user_features)
{
/*
* For the current set of features the bits just coincide
*/
return (unsigned int)user_features;
}
/*
* userland asks for a certain API version and we return which bits
* and ioctl commands are implemented in this kernel for such API
@ -1202,19 +1292,21 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx,
ret = -EFAULT;
if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api)))
goto out;
if (uffdio_api.api != UFFD_API || uffdio_api.features) {
if (uffdio_api.api != UFFD_API ||
(uffdio_api.features & ~UFFD_API_FEATURES)) {
memset(&uffdio_api, 0, sizeof(uffdio_api));
if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
goto out;
ret = -EINVAL;
goto out;
}
uffdio_api.features = UFFD_API_FEATURES;
uffdio_api.features &= UFFD_API_FEATURES;
uffdio_api.ioctls = UFFD_API_IOCTLS;
ret = -EFAULT;
if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
goto out;
ctx->state = UFFD_STATE_RUNNING;
ctx->features = uffd_ctx_features(uffdio_api.features);
ret = 0;
out:
return ret;
@ -1301,6 +1393,7 @@ static void init_once_userfaultfd_ctx(void *mem)
init_waitqueue_head(&ctx->fault_pending_wqh);
init_waitqueue_head(&ctx->fault_wqh);
init_waitqueue_head(&ctx->event_wqh);
init_waitqueue_head(&ctx->fd_wqh);
seqcount_init(&ctx->refile_seq);
}
@ -1341,6 +1434,7 @@ static struct file *userfaultfd_file_create(int flags)
atomic_set(&ctx->refcount, 1);
ctx->flags = flags;
ctx->features = 0;
ctx->state = UFFD_STATE_WAIT_API;
ctx->released = false;
ctx->mm = current->mm;