Turn on/off SVM dynamically at run time.

This is needed for coexistence with VirtualBox.

Author: Taogle2018

arch/x86/kvm/svm.c

@@ -542,35 +542,24 @@ static int has_svm(void)
 	return static_cpu_has(X86_FEATURE_SVM);
 }
 
-static inline void cpu_svm_disable(void)
-{
-	uint64_t efer;
-
-	wrmsrl(MSR_VM_HSAVE_PA, 0);
-	rdmsrl(MSR_EFER, efer);
-	wrmsrl(MSR_EFER, efer & ~EFER_SVME);
-}
-
 static void svm_hardware_disable(void)
 {
-	cpu_svm_disable();
-
 	//amd_pmu_disable_virt();
 }
 
+/*
+ * This does not turn on SVM as Linus does now, as on Windows coexistence with
+ * other VMMs is important and requires turning on/off SVM dynamically at run
+ * time.
+ */
 static int svm_hardware_enable(void)
 {
 
 	struct svm_cpu_data *sd;
-	uint64_t efer;
 	struct desc_ptr gdt_descr;
 	struct desc_struct *gdt;
 	int me = raw_smp_processor_id();
 
-	rdmsrl(MSR_EFER, efer);
-	if (efer & EFER_SVME)
-		return -EBUSY;
-
 	if (!has_svm()) {
 		pr_err("%s: err EOPNOTSUPP on %d\n", __func__, me);
 		return -EINVAL;
@@ -589,11 +578,6 @@ static int svm_hardware_enable(void)
 	gdt = (struct desc_struct *)gdt_descr.address;
 	sd->tss_desc = (struct kvm_ldttss_desc *)(gdt + GDT_ENTRY_TSS);
 
-	wrmsrl(MSR_EFER, efer | EFER_SVME);
-
-	wrmsrl(MSR_VM_HSAVE_PA, page_to_pfn(sd->save_area) << PAGE_SHIFT);
-
-
 	/*
 	 * Get OSVW bits.
 	 *
@@ -4220,6 +4204,10 @@ static void svm_cancel_injection(struct kvm_vcpu *vcpu)
 static void svm_vcpu_run(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
+	int me = raw_smp_processor_id();
+	struct svm_cpu_data *sd;
+	uint64_t efer, hsave_pa = 0;
+	uint64_t svm_enabled;
 
 	svm->vmcb->save.rax = vcpu->arch.regs[VCPU_REGS_RAX];
 	svm->vmcb->save.rsp = vcpu->arch.regs[VCPU_REGS_RSP];
@@ -4238,6 +4226,15 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
 
 	svm->vmcb->save.cr2 = vcpu->arch.cr2;
 
+	sd = per_cpu(svm_data, me);
+	rdmsrl(MSR_EFER, efer);
+	svm_enabled = !!(efer & EFER_SVME);
+	if (!svm_enabled)
+		wrmsrl(MSR_EFER, efer | EFER_SVME);
+	else
+		rdmsrl(MSR_VM_HSAVE_PA, hsave_pa);
+	wrmsrl(MSR_VM_HSAVE_PA, page_to_pfn(sd->save_area) << PAGE_SHIFT);
+
 	clgi();
 
 	local_irq_enable();
@@ -4265,6 +4262,10 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
 
 	stgi();
 
+	wrmsrl(MSR_VM_HSAVE_PA, hsave_pa);
+	if (!svm_enabled)
+		wrmsrl(MSR_EFER, efer);
+
 	/* Any pending NMI will happen here */
 
 	if (unlikely(svm->vmcb->control.exit_code == SVM_EXIT_NMI))