KVM: Add documentation for kvm->srcu lock

This patch documents the kvm->srcu lock (using the information from
a mail which has been posted by Marcelo Tosatti to the kvm mailing
list some months ago, see the following URL for details:
http://www.mail-archive.com/kvm@vger.kernel.org/msg90040.html )

Signed-off-by: Thomas Huth <thuth@linux.vnet.ibm.com>
Reviewed-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/Documentation/virtual/kvm/locking.txt b/Documentation/virtual/kvm/locking.txt
index 41b7ac9884b5..a9f366e73c8e 100644
--- a/Documentation/virtual/kvm/locking.txt
+++ b/Documentation/virtual/kvm/locking.txt
@@ -151,3 +151,14 @@ Type:		spinlock_t
 Arch:           any
 Protects:       -shadow page/shadow tlb entry
 Comment:        it is a spinlock since it is used in mmu notifier.
+
+Name:           kvm->srcu
+Type:           srcu lock
+Arch:           any
+Protects:       - kvm->memslots
+                - kvm->buses
+Comment:        The srcu read lock must be held while accessing memslots (e.g.
+                when using gfn_to_* functions) and while accessing in-kernel
+                MMIO/PIO address->device structure mapping (kvm->buses).
+                The srcu index can be stored in kvm_vcpu->srcu_idx per vcpu
+                if it is needed by multiple functions.