linux-kernel - [PATCH] KVM: document lock orders

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Message-Id: <1476357057-17899-1-git-send-email-pbonzini@redhat.com>
Date:   Thu, 13 Oct 2016 13:10:57 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     rkrcmar@...hat.com
Subject: [PATCH] KVM: document lock orders

This is long overdue, and not really hard.

Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 Documentation/virtual/kvm/locking.txt | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/Documentation/virtual/kvm/locking.txt b/Documentation/virtual/kvm/locking.txt
index f2491a8c68b4..e5dd9f4d6100 100644
--- a/Documentation/virtual/kvm/locking.txt
+++ b/Documentation/virtual/kvm/locking.txt
@@ -4,7 +4,17 @@ KVM Lock Overview
 1. Acquisition Orders
 ---------------------
 
-(to be written)
+The acquisition orders for mutexes are as follows:
+
+- kvm->lock is taken outside vcpu->mutex
+
+- kvm->lock is taken outside kvm->slots_lock and kvm->irq_lock
+
+- kvm->slots_lock is taken outside kvm->irq_lock, though acquiring
+  them together is quite rare.
+
+For spinlocks, kvm_lock is taken outside kvm->mmu_lock.  Everything
+else is a leaf: no other lock is taken inside the critical sections.
 
 2: Exception
 ------------
-- 
2.7.4