KVM: MMU: document write_flooding_count
Document write_flooding_count to Documentation/virtual/kvm/mmu.txt
Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/Documentation/virtual/kvm/mmu.txt b/Documentation/virtual/kvm/mmu.txt
index f514a3f..0db7743 100644
--- a/Documentation/virtual/kvm/mmu.txt
+++ b/Documentation/virtual/kvm/mmu.txt
@@ -215,6 +215,15 @@
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
===========
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 5d28c11..6b636fd 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -233,6 +233,7 @@
int clear_spte_count;
#endif
+ /* Number of writes since the last time traversal visited this page. */
int write_flooding_count;
};