[PATCH] SVM: reliably detect if SVM was disabled by BIOS

["Joerg Roedel" <joerg.roedel@amd.com>]

From: Joerg Roedel <joerg.roedel@amd.com>

This patch adds an implementation to the svm is_disabled function to
detect reliably if the BIOS disabled the SVM feature in the CPU. This
fixes the issues with kernel panics when loading the kvm-amd module on
machines where SVM is available but disabled.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

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 System    |                  Register Court Dresden: HRA 4896
 Research  |              General Partner authorized to represent:
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diff --git a/drivers/kvm/svm.c b/drivers/kvm/svm.c
index fa17d6d..54aa83a 100644
--- a/drivers/kvm/svm.c
+++ b/drivers/kvm/svm.c
@@ -1727,6 +1727,12 @@ static void svm_inject_page_fault(struct kvm_vcpu *vcpu,
 
 static int is_disabled(void)
 {
+	uint64_t vm_cr;
+
+	rdmsrl(MSR_VM_CR, vm_cr);
+	if (vm_cr & (1 << SVM_VM_CR_SVM_DISABLE))
+		return 1;
+
 	return 0;
 }
 
diff --git a/drivers/kvm/svm.h b/drivers/kvm/svm.h
index 5e93814..005a9c5 100644
--- a/drivers/kvm/svm.h
+++ b/drivers/kvm/svm.h
@@ -175,8 +175,11 @@ struct __attribute__ ((__packed__)) vmcb {
 #define SVM_CPUID_FUNC 0x8000000a
 
 #define MSR_EFER_SVME_MASK (1ULL << 12)
+#define MSR_VM_CR       0xc0010114ULL
 #define MSR_VM_HSAVE_PA 0xc0010117ULL
 
+#define SVM_VM_CR_SVM_DISABLE 4
+
 #define SVM_SELECTOR_S_SHIFT 4
 #define SVM_SELECTOR_DPL_SHIFT 5
 #define SVM_SELECTOR_P_SHIFT 7