KVM: MMU: document write_flooding_count

[karo-tx-linux.git] / Documentation / virtual / kvm / mmu.txt

diff --git a/Documentation/virtual/kvm/mmu.txt b/Documentation/virtual/kvm/mmu.txt
index f514a3fad9b983be1d03af8fb2fd86b390579979..0db7743c55e15e60a32ed2ded4bd6bd51813bb28 100644 (file)
--- a/Documentation/virtual/kvm/mmu.txt
+++ b/Documentation/virtual/kvm/mmu.txt
@@ -215,6 +215,15 @@ Shadow pages contain the following information:
     atomically.  The reader uses this while running out of the MMU lock
     to detect in-progress updates and retry them until the writer has
     finished the write.
+  write_flooding_count:
+    A guest may write to a page table many times, causing a lot of
+    emulations if the page needs to be write-protected (see "Synchronized
+    and unsynchronized pages" below).  Leaf pages can be unsynchronized
+    so that they do not trigger frequent emulation, but this is not
+    possible for non-leafs.  This field counts the number of emulations
+    since the last time the page table was actually used; if emulation
+    is triggered too frequently on this page, KVM will unmap the page
+    to avoid emulation in the future.
 
 Reverse map
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