From: Anthony Liguori <aliguori-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
Subject: [PATCH][SVM] Only save/restore MSRs when needed

  We only have to save/restore MSR_GS_BASE on every VMEXIT.  The rest can be
  saved/restored when we leave the VCPU.  As a special case, MSR_IA32_DEBUGCTL
  only needs to be saved/restored on every exit if debugging is enabled in
  either the host or the guest.

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

Index: kernel/drivers/kvm/svm.c
===================================================================
--- kernel.orig/drivers/kvm/svm.c	2007-04-27 17:52:37.200780944 -0500
+++ kernel/drivers/kvm/svm.c	2007-04-27 18:14:02.098446808 -0500
@@ -611,7 +611,7 @@
 
 static void svm_vcpu_load(struct kvm_vcpu *vcpu)
 {
-	int cpu;
+	int cpu, i;
 
 	cpu = get_cpu();
 	if (unlikely(cpu != vcpu->cpu)) {
@@ -626,10 +626,24 @@
 		vcpu->svm->vmcb->control.tsc_offset += delta;
 		vcpu->cpu = cpu;
 	}
+
+	for (i = 0; i < NR_HOST_SAVE_USER_MSRS; i++)
+		rdmsrl(host_save_user_msrs[i], vcpu->svm->host_user_msrs[i]);
+
+	rdmsrl(MSR_IA32_DEBUGCTLMSR, vcpu->svm->host_ia32_debugctl);
 }
 
 static void svm_vcpu_put(struct kvm_vcpu *vcpu)
 {
+	int i;
+
+	for (i = 0; i < NR_HOST_SAVE_USER_MSRS; i++)
+		wrmsrl(host_save_user_msrs[i], vcpu->svm->host_user_msrs[i]);
+
+	wrmsrl(MSR_IA32_DEBUGCTLMSR, vcpu->svm->host_ia32_debugctl);
+	/* FIXME: LASTBRANCHFROMIP, LASTBRANCHTOIP, LASTINTFROMIP,
+	   LASTINTTOIP */
+
 	rdtscll(vcpu->host_tsc);
 	put_cpu();
 }
@@ -815,18 +829,16 @@
 
 static void load_host_msrs(struct kvm_vcpu *vcpu)
 {
-	int i;
-
-	for ( i = 0; i < NR_HOST_SAVE_MSRS; i++)
-		wrmsrl(host_save_msrs[i], vcpu->svm->host_msrs[i]);
+#ifdef CONFIG_X86_64
+	wrmsrl(MSR_GS_BASE, vcpu->svm->host_gs_base);
+#endif
 }
 
 static void save_host_msrs(struct kvm_vcpu *vcpu)
 {
-	int i;
-
-	for ( i = 0; i < NR_HOST_SAVE_MSRS; i++)
-		rdmsrl(host_save_msrs[i], vcpu->svm->host_msrs[i]);
+#ifdef CONFIG_X86_64
+	rdmsrl(MSR_GS_BASE, vcpu->svm->host_gs_base);
+#endif
 }
 
 static void new_asid(struct kvm_vcpu *vcpu, struct svm_cpu_data *svm_data)
@@ -1498,6 +1510,11 @@
 		load_db_regs(vcpu->svm->db_regs);
 	}
 
+	if ((vcpu->svm->vmcb->save.dr7 & 0xff) ||
+	    (vcpu->svm->host_dr7 & 0xff)) {
+		wrmsrl(MSR_IA32_DEBUGCTLMSR, vcpu->svm->host_ia32_debugctl);
+	}
+
 	if (vcpu->fpu_active) {
 		fx_save(vcpu->host_fx_image);
 		fx_restore(vcpu->guest_fx_image);
@@ -1617,6 +1634,11 @@
 		fx_restore(vcpu->host_fx_image);
 	}
 
+	if ((vcpu->svm->vmcb->save.dr7 & 0xff) ||
+	    (vcpu->svm->host_dr7 & 0xff)) {
+		rdmsrl(MSR_IA32_DEBUGCTLMSR, vcpu->svm->host_ia32_debugctl);
+	}
+
 	if ((vcpu->svm->vmcb->save.dr7 & 0xff))
 		load_db_regs(vcpu->svm->host_db_regs);
 
Index: kernel/drivers/kvm/kvm_svm.h
===================================================================
--- kernel.orig/drivers/kvm/kvm_svm.h	2007-04-27 17:52:37.240774864 -0500
+++ kernel/drivers/kvm/kvm_svm.h	2007-04-27 17:53:42.509852456 -0500
@@ -9,17 +9,15 @@
 #include "svm.h"
 #include "kvm.h"
 
-static const u32 host_save_msrs[] = {
+static const u32 host_save_user_msrs[] = {
 #ifdef CONFIG_X86_64
 	MSR_STAR, MSR_LSTAR, MSR_CSTAR, MSR_SYSCALL_MASK, MSR_KERNEL_GS_BASE,
-	MSR_FS_BASE, MSR_GS_BASE,
+	MSR_FS_BASE,
 #endif
 	MSR_IA32_SYSENTER_CS, MSR_IA32_SYSENTER_ESP, MSR_IA32_SYSENTER_EIP,
-	MSR_IA32_DEBUGCTLMSR, /*MSR_IA32_LASTBRANCHFROMIP,
-	MSR_IA32_LASTBRANCHTOIP, MSR_IA32_LASTINTFROMIP,MSR_IA32_LASTINTTOIP,*/
 };
 
-#define NR_HOST_SAVE_MSRS ARRAY_SIZE(host_save_msrs)
+#define NR_HOST_SAVE_USER_MSRS ARRAY_SIZE(host_save_user_msrs)
 #define NUM_DB_REGS 4
 
 struct vcpu_svm {
@@ -32,7 +30,9 @@
 
 	u64 next_rip;
 
-	u64 host_msrs[NR_HOST_SAVE_MSRS];
+	u64 host_user_msrs[NR_HOST_SAVE_USER_MSRS];
+	u64 host_ia32_debugctl;
+	u64 host_gs_base;
 	unsigned long host_cr2;
 	unsigned long host_db_regs[NUM_DB_REGS];
 	unsigned long host_dr6;