[PATCH] SVM: enable LBRV virtualization if available

["Joerg Roedel" <joerg.roedel-5C7GfCeVMHo@public.gmane.org>]

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From: Joerg Roedel <joerg.roedel-5C7GfCeVMHo@public.gmane.org>

This patch enables the virtualization of the last branch record MSRs on
SVM if this feature is available in hardware. It also introduces a small
and simple check feature for specific SVM extensions.

Signed-off-by: Joerg Roedel <joerg.roedel-5C7GfCeVMHo@public.gmane.org>

-- 
Joerg Roedel
Operating System Research Center
AMD Saxony LLC & Co. KG

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diff --git a/drivers/kvm/svm.c b/drivers/kvm/svm.c
index ddc0505..421eeb8 100644
--- a/drivers/kvm/svm.c
+++ b/drivers/kvm/svm.c
@@ -44,6 +44,12 @@ MODULE_LICENSE("GPL");
 #define KVM_EFER_LMA (1 << 10)
 #define KVM_EFER_LME (1 << 8)
 
+#define SVM_FEATURE_NPT  (1 << 0)
+#define SVM_FEATURE_LBRV (1 << 1)
+#define SVM_DEATURE_SVML (1 << 2)
+
+#define svm_has(feat) (svm_features & (feat))
+
 unsigned long iopm_base;
 unsigned long msrpm_base;
 
@@ -68,6 +74,7 @@ struct svm_cpu_data {
 };
 
 static DEFINE_PER_CPU(struct svm_cpu_data *, svm_data);
+static uint32_t svm_features;
 
 struct svm_init_data {
 	int cpu;
@@ -309,6 +316,7 @@ static void svm_hardware_enable(void *garbage)
 	svm_data->asid_generation = 1;
 	svm_data->max_asid = cpuid_ebx(SVM_CPUID_FUNC) - 1;
 	svm_data->next_asid = svm_data->max_asid + 1;
+	svm_features = cpuid_edx(SVM_CPUID_FUNC);
 
 	asm volatile ( "sgdt %0" : "=m"(gdt_descr) );
 	gdt = (struct desc_struct *)gdt_descr.address;
@@ -518,6 +526,8 @@ static void init_vmcb(struct vmcb *vmcb)
 	rdtscll(tsc);
 	control->tsc_offset = -tsc;
 	control->int_ctl = V_INTR_MASKING_MASK;
+	if (svm_has(SVM_FEATURE_LBRV))
+		control->lbr_ctl = 1ULL;
 
 	init_seg(&save->es);
 	init_seg(&save->ss);

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