From: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
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.
Signed-off-by: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
---
fs/userfaultfd.c | 98 ++++++++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 96 insertions(+), 2 deletions(-)
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index b4f790f..76205b3 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -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 */
@@ -135,6 +140,8 @@ 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);
@@ -423,6 +430,59 @@ int handle_userfault(struct fault_env *fe, 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;
@@ -511,6 +571,12 @@ 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;
@@ -542,6 +608,9 @@ 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);
@@ -606,6 +675,19 @@ 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;
@@ -1149,6 +1231,14 @@ 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
@@ -1167,19 +1257,21 @@ 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;
@@ -1266,6 +1358,7 @@ 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);
}
@@ -1306,6 +1399,7 @@ 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;
--
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