[PATCH 3/7] KVM: MMU: document write_flooding_count

From: Xiao Guangrong
Date: Wed Jun 19 2013 - 05:13:44 EST

Document write_flooding_count to Documentation/virtual/kvm/mmu.txt

Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
Documentation/virtual/kvm/mmu.txt | 8 ++++++++
arch/x86/include/asm/kvm_host.h | 5 +++++
2 files changed, 13 insertions(+)

diff --git a/Documentation/virtual/kvm/mmu.txt b/Documentation/virtual/kvm/mmu.txt
index ce6df51..5a6b2e2 100644
--- a/Documentation/virtual/kvm/mmu.txt
+++ b/Documentation/virtual/kvm/mmu.txt
@@ -214,6 +214,14 @@ Shadow pages contain the following information:
It is only used on 32bit host which helps us to detect whether updating the
64bit spte is complete so that we can avoid reading the truncated value out
of mmu-lock.
+ write_flooding_count:
+ In order to sync the page table between guest and host, the page sometimes
+ needs to be write-protected (see "Synchronized and unsynchronized pages"
+ below), any write to the page can cause write emulation. If the emulation
+ on the page is too frequent we'd better unmap the page to avoid the
+ future emulation. write_flooding_count aims at this optimization which is
+ increased when the page needs to be write emulated and cleared when the
+ page is actually used.

Reverse map
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 1dac2c1..5eb5382 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -234,6 +234,11 @@ struct kvm_mmu_page {
int clear_spte_count;

+ /*
+ * Increased when the page needs to be write emulated, cleared
+ * when the page is actually used as page table to avoid frequent
+ * emulation on the page.
+ */
int write_flooding_count;


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