Set the FRED_VIRT_ENABLE bit (bit 4) in the misc_ctl2 field of the VMCB to
enable FRED virtualization. This enables hardware to automatically save and
restore the FRED MSRs on VMRUN and #VMEXIT.

Set the bit in svm_vcpu_after_set_cpuid() when FRED is exposed to the
guest, and clear it otherwise.

FRED virtualization requires vNMI to handle guest NMIs correctly, so, clear
FRED when vNMI is unavailable.

Signed-off-by: Shivansh Dhiman <shivansh.dhiman@amd.com>
---

Changes in v3:
* Renamed FRED_VIRT_ENABLE_MASK to SVM_MISC2_ENABLE_V_FRED.
* Set the bit in misc_ctl2, the current name of the VMCB field.
* Removed the unconditional kvm_cpu_cap_clear(X86_FEATURE_FRED).
* Clear FRED when vNMI is unavailable (Andrew Cooper).

Changes in v2:
* Confined the enabling of vFRED to svm_vcpu_after_set_cpuid() only
  (Sean Christopherson).

---
 arch/x86/include/asm/svm.h |  1 +
 arch/x86/kvm/svm/svm.c     | 11 ++++++++---
 2 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
index 1a6d4509b05b..288a8a78f1c7 100644
--- a/arch/x86/include/asm/svm.h
+++ b/arch/x86/include/asm/svm.h
@@ -250,6 +250,7 @@ struct __attribute__ ((__packed__)) vmcb_control_area {
 
 #define SVM_MISC2_ENABLE_V_LBR	BIT_ULL(0)
 #define SVM_MISC2_ENABLE_V_VMLOAD_VMSAVE	BIT_ULL(1)
+#define SVM_MISC2_ENABLE_V_FRED BIT_ULL(4)
 
 #define SVM_TSC_RATIO_RSVD	0xffffff0000000000ULL
 #define SVM_TSC_RATIO_MIN	0x0000000000000001ULL
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 86a3ba54aab2..25dd379725d4 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4912,6 +4912,11 @@ static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 	if (guest_cpuid_is_intel_compatible(vcpu))
 		guest_cpu_cap_clear(vcpu, X86_FEATURE_V_VMSAVE_VMLOAD);
 
+	if (guest_cpu_cap_has(vcpu, X86_FEATURE_FRED))
+		svm->vmcb->control.misc_ctl2 |= SVM_MISC2_ENABLE_V_FRED;
+	else
+		svm->vmcb->control.misc_ctl2 &= ~SVM_MISC2_ENABLE_V_FRED;
+
 	if (is_sev_guest(vcpu))
 		sev_vcpu_after_set_cpuid(svm);
 }
@@ -5675,9 +5680,6 @@ static __init void svm_set_cpu_caps(void)
 
 	kvm_cpu_cap_clear(X86_FEATURE_IBT);
 
-	/* SVM FRED virtualization not implemented yet */
-	kvm_cpu_cap_clear(X86_FEATURE_FRED);
-
 	/* CPUID 0x80000001 and 0x8000000A (SVM features) */
 	if (nested) {
 		kvm_cpu_cap_set(X86_FEATURE_SVM);
@@ -5751,6 +5753,9 @@ static __init void svm_set_cpu_caps(void)
 	/* CPUID 0x8000001F (SME/SEV features) */
 	sev_set_cpu_caps();
 
+	if (!vnmi)
+		kvm_cpu_cap_clear(X86_FEATURE_FRED);
+
 	/*
 	 * Clear capabilities that are automatically configured by common code,
 	 * but that require explicit SVM support (that isn't yet implemented).
-- 
2.43.0