[PATCH] KVM: Start lock documentation

[Jan Kiszka <jan.kiszka@siemens.com>]

The goal of this document shall be
- overview of all locks used in KVM core
- provide details on the scope of each lock
- explain the lock type, specifically of a raw spin locks
- provide a lock ordering guide

Start with one dependency chain and two locks.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---
 Documentation/kvm/locking.txt |   30 ++++++++++++++++++++++++++++++
 1 files changed, 30 insertions(+), 0 deletions(-)
 create mode 100644 Documentation/kvm/locking.txt

diff --git a/Documentation/kvm/locking.txt b/Documentation/kvm/locking.txt
new file mode 100644
index 0000000..23f9092
--- /dev/null
+++ b/Documentation/kvm/locking.txt
@@ -0,0 +1,30 @@
+KVM Lock Overview
+=================
+
+1. Acquisition Orders
+---------------------
+
+kvm_lock
++-> kvm::srcu / kvm::lock
+    +-> kvm::slots_lock
+        +-> kvm::mmu_lock
+...
+
+
+2. Reference
+------------
+
+Name:		kvm_lock
+Type:		raw_spinlock
+Arch:		any
+Protects:	- vm_list
+		- hardware virtualization enable/disable
+Comment:	'raw' because hardware enabling/disabling must be atomic /wrt
+		migration.
+
+Name:		kvm_arch::tsc_write_lock
+Type:		raw_spinlock
+Arch:		x86
+Protects:	- kvm_arch::{last_tsc_write,last_tsc_nsec,last_tsc_offset}
+		- tsc offset in vmcb
+Comment:	'raw' because updating the tsc offsets must not be preempted.
-- 
1.7.1