[PATCH 3/5] ioeventfd: Introduce KVM_IOEVENTFD_FLAG_READ

[Sasha Levin <levinsasha928@gmail.com>]

The new flag specifies whether reads from the address specified
in the ioeventfd will raise the event like writes do.

The read value will be the one passed in datamatch.

Cc: Avi Kivity <avi@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
---
 Documentation/virtual/kvm/api.txt |    5 +++++
 include/linux/kvm.h               |    2 ++
 virt/kvm/eventfd.c                |   24 ++++++++++++++++++++++++
 3 files changed, 31 insertions(+), 0 deletions(-)

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 7994840..8179bc1 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1346,10 +1346,15 @@ The following flags are defined:
 #define KVM_IOEVENTFD_FLAG_DATAMATCH (1 << kvm_ioeventfd_flag_nr_datamatch)
 #define KVM_IOEVENTFD_FLAG_PIO       (1 << kvm_ioeventfd_flag_nr_pio)
 #define KVM_IOEVENTFD_FLAG_DEASSIGN  (1 << kvm_ioeventfd_flag_nr_deassign)
+#define KVM_IOEVENTFD_FLAG_READ      (1 << kvm_ioeventfd_flag_nr_read)
 
 If datamatch flag is set, the event will be signaled only if the written value
 to the registered address is equal to datamatch in struct kvm_ioeventfd.
 
+If the read flag is set, the event will be signaled when the specified address
+is being read from. The value actually read by the guest will be the value
+passed in datamatch.
+
 5. The kvm_run structure
 
 Application code obtains a pointer to the kvm_run structure by
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 81cd295..ce4cc89 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -387,12 +387,14 @@ enum {
 	kvm_ioeventfd_flag_nr_datamatch,
 	kvm_ioeventfd_flag_nr_pio,
 	kvm_ioeventfd_flag_nr_deassign,
+	kvm_ioeventfd_flag_nr_read,
 	kvm_ioeventfd_flag_nr_max,
 };
 
 #define KVM_IOEVENTFD_FLAG_DATAMATCH (1 << kvm_ioeventfd_flag_nr_datamatch)
 #define KVM_IOEVENTFD_FLAG_PIO       (1 << kvm_ioeventfd_flag_nr_pio)
 #define KVM_IOEVENTFD_FLAG_DEASSIGN  (1 << kvm_ioeventfd_flag_nr_deassign)
+#define KVM_IOEVENTFD_FLAG_READ      (1 << kvm_ioeventfd_flag_nr_read)
 
 #define KVM_IOEVENTFD_VALID_FLAG_MASK  ((1 << kvm_ioeventfd_flag_nr_max) - 1)
 
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index a1a3f66..e0f24bf 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -428,6 +428,7 @@ struct _ioeventfd {
 	u64                  datamatch;
 	struct kvm_io_device dev;
 	bool                 wildcard;
+	bool                 track_reads;
 };
 
 static inline struct _ioeventfd *
@@ -522,6 +523,24 @@ ioeventfd_write(struct kvm_io_device *this, gpa_t addr, int len,
 	return 0;
 }
 
+/* MMIO/PIO reads trigger an event if the addr/val match */
+static int
+ioeventfd_read(struct kvm_io_device *this, gpa_t addr, int len,
+		void *val)
+{
+	struct _ioeventfd *p = to_ioeventfd(this);
+
+	/* Exit if signaling on reads isn't requested */
+	if (!p->track_reads)
+		return -EOPNOTSUPP;
+
+	if (!ioeventfd_in_range(p, addr, len, val))
+		return -EOPNOTSUPP;
+
+	eventfd_signal(p->eventfd, 1);
+	return 0;
+}
+
 /*
  * This function is called as KVM is completely shutting down.  We do not
  * need to worry about locking just nuke anything we have as quickly as possible
@@ -535,6 +554,7 @@ ioeventfd_destructor(struct kvm_io_device *this)
 }
 
 static const struct kvm_io_device_ops ioeventfd_ops = {
+	.read       = ioeventfd_read,
 	.write      = ioeventfd_write,
 	.destructor = ioeventfd_destructor,
 };
@@ -600,6 +620,10 @@ kvm_assign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
 		goto unlock_fail;
 	}
 
+	/* Raise signal on reads from address if requested */
+	if (args->flags & KVM_IOEVENTFD_FLAG_READ)
+		p->track_reads = true;
+
 	kvm_iodevice_init(&p->dev, &ioeventfd_ops);
 
 	ret = kvm_io_bus_register_dev(kvm, bus_idx, &p->dev);
-- 
1.7.6