[PATCH][SVM] Only save/restore MSRs when needed

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

[-- Attachment #1: Type: text/plain, Size: 325 bytes --]

I've tested this with 32-bit and 64-bit guests on a 64-bit host and with 
32-bit guests on a 32-bit host.

I *think* it's doing the right thing wrt to DEBUGCTL but an extra set of 
eyes would be helpful.

Depending on my machine's mood, we're at somewhere between 3200 and 2700 
cycles per VMEXIT.

Regards,

Anthony Liguori

[-- Attachment #2: svm-lazy-msrs.diff --]
[-- Type: text/x-patch, Size: 3881 bytes --]

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;

[-- Attachment #3: Type: text/plain, Size: 286 bytes --]

-------------------------------------------------------------------------
This SF.net email is sponsored by DB2 Express
Download DB2 Express C - the FREE version of DB2 express and take
control of your XML. No limits. Just data. Click to get it now.
http://sourceforge.net/powerbar/db2/

[-- Attachment #4: Type: text/plain, Size: 186 bytes --]

_______________________________________________
kvm-devel mailing list
kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
https://lists.sourceforge.net/lists/listinfo/kvm-devel