[PATCH 3/3] Eliminate read_cr3 on TLB flush

[Anthony Liguori <aliguori-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

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Regards,

Anthony Liguori

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Subject: [PATCH][PARAVIRT] Eliminate unnecessary CR3 read in TLB flush

This patch eliminates the CR3 read (which would cause a VM exit) in the TLB
flush path.  The patch is based on Ingo Molnar's paravirt series.

Signed-off-by: Anthony Liguori <aliguori-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>

Index: kvm/arch/i386/kernel/kvm.c
===================================================================
--- kvm.orig/arch/i386/kernel/kvm.c	2007-05-30 09:13:48.000000000 -0500
+++ kvm/arch/i386/kernel/kvm.c	2007-05-30 09:14:24.000000000 -0500
@@ -24,11 +24,35 @@
 #include <linux/kernel.h>
 #include <linux/kvm_para.h>
 #include <linux/cpu.h>
+#include <linux/mm.h>
+#include <asm/processor.h>
+#include <asm/tlbflush.h>
 
 static DEFINE_PER_CPU(struct kvm_vcpu_para_state, para_state);
 extern unsigned char hypercall_addr[4];
 
 /*
+ * Avoid the VM exit upon cr3 load by using the cached
+ * ->active_mm->pgd value:
+ */
+static void kvm_flush_tlb_user(void)
+{
+	write_cr3(__pa(current->active_mm->pgd));
+}
+
+/*
+ * Avoid VM exit for cr3 read by calling into kvm_flush_tlb_user
+ */
+static fastcall void kvm_flush_tlb_kernel(void)
+{
+	unsigned long orig_cr4 = read_cr4();
+
+	write_cr4(orig_cr4 & ~X86_CR4_PGE);
+	kvm_flush_tlb_user();
+	write_cr4(orig_cr4);
+}
+
+/*
  * No need for any "IO delay" on KVM
  */
 static void kvm_io_delay(void)
@@ -38,6 +62,8 @@
 static void kvm_guest_setup(void)
 {
 	paravirt_ops.name = "KVM";
+	paravirt_ops.flush_tlb_user = kvm_flush_tlb_user;
+	paravirt_ops.flush_tlb_kernel = kvm_flush_tlb_kernel;
 	paravirt_ops.io_delay = kvm_io_delay;
 	paravirt_ops.paravirt_enabled = 1;
 }

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