[PATCH 4/6] KVM MMU: optimize for writing cr4

[Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>]

Usually, OS changes CR4.PGE bit to flush all global page, under this
case, no need reset mmu and just flush tlb

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
---
 arch/x86/kvm/x86.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fd5c3d3..2aaa6fb 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -463,6 +463,15 @@ void kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 	unsigned long old_cr4 = kvm_read_cr4(vcpu);
 	unsigned long pdptr_bits = X86_CR4_PGE | X86_CR4_PSE | X86_CR4_PAE;
 
+	if (cr4 == old_cr4)
+		return;
+
+	if ((cr4 ^ old_cr4) == X86_CR4_PGE) {
+		kvm_mmu_sync_roots(vcpu);
+		kvm_mmu_flush_tlb(vcpu);
+		return;
+	}
+
 	if (cr4 & CR4_RESERVED_BITS) {
 		kvm_inject_gp(vcpu, 0);
 		return;
-- 
1.6.1.2