[PATCH v10 11/28] KVM: x86: Add a helper to detect if FRED is enabled for a vCPU

[Sohil Mehta <sohil.mehta@intel.com>]

From: "Xin Li (Intel)" <xin@zytor.com>

Add is_fred_enabled() to detect if FRED is enabled on a vCPU.

Signed-off-by: Xin Li (Intel) <xin@zytor.com>
[ Sean: removed the "kvm_" prefix from the function name ]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sohil Mehta <sohil.mehta@intel.com>
Tested-by: Shan Kang <shan.kang@intel.com>
Tested-by: Xuelian Guo <xuelian.guo@intel.com>
Reviewed-by: Chao Gao <chao.gao@intel.com>
---
v10:
 - Add back the change log (Binbin Wu and Sean).
---
 arch/x86/kvm/regs.h | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/arch/x86/kvm/regs.h b/arch/x86/kvm/regs.h
index 447f0ec3e63e..4e641a6c20f9 100644
--- a/arch/x86/kvm/regs.h
+++ b/arch/x86/kvm/regs.h
@@ -364,6 +364,21 @@ static __always_inline bool kvm_is_cr4_bit_set(struct kvm_vcpu *vcpu,
 	return !!kvm_read_cr4_bits(vcpu, cr4_bit);
 }
 
+/*
+ * It's enough to check just CR4.FRED (X86_CR4_FRED) to tell if
+ * a vCPU is running with FRED enabled, because:
+ * 1) CR4.FRED can be set to 1 only _after_ IA32_EFER.LMA = 1.
+ * 2) To leave IA-32e mode, CR4.FRED must be cleared first.
+ */
+static inline bool is_fred_enabled(struct kvm_vcpu *vcpu)
+{
+#ifdef CONFIG_X86_64
+	return kvm_is_cr4_bit_set(vcpu, X86_CR4_FRED);
+#else
+	return false;
+#endif
+}
+
 static inline ulong kvm_read_cr3(struct kvm_vcpu *vcpu)
 {
 	if (!kvm_register_is_available(vcpu, VCPU_REG_CR3))
-- 
2.43.0