linux-kernel - [PATCH 7/7] KVM: SVM: Enable save/restore of FRED MSRs

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Message-ID: <20260129063653.3553076-8-shivansh.dhiman@amd.com>
Date: Thu, 29 Jan 2026 06:36:53 +0000
From: Shivansh Dhiman <shivansh.dhiman@....com>
To: <seanjc@...gle.com>, <pbonzini@...hat.com>,
	<linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>
CC: <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>, <x86@...nel.org>, <hpa@...or.com>,
	<xin@...or.com>, <nikunj.dadhania@....com>, <santosh.shukla@....com>
Subject: [PATCH 7/7] KVM: SVM: Enable save/restore of FRED MSRs

Set the FRED_VIRT_ENABLE bit (bit 4) in the VIRT_EXT field of VMCB to enable
FRED Virtualization for the guest. This enables automatic save/restore of
FRED MSRs. Also toggle this bit when setting CPUIDs, to support booting of
secure guests.

Signed-off-by: Shivansh Dhiman <shivansh.dhiman@....com>
---
 arch/x86/kvm/svm/svm.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 954df4eae90e..24579c149937 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1144,6 +1144,9 @@ static void init_vmcb(struct kvm_vcpu *vcpu, bool init_event)
 	save->fred_ssp3 = 0;
 	save->fred_config = 0;
 
+	if (guest_cpu_cap_has(vcpu, X86_FEATURE_FRED))
+		svm->vmcb->control.virt_ext |= FRED_VIRT_ENABLE_MASK;
+
 	init_sys_seg(&save->ldtr, SEG_TYPE_LDT);
 	init_sys_seg(&save->tr, SEG_TYPE_BUSY_TSS16);
 
@@ -4529,6 +4532,9 @@ 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.virt_ext |= FRED_VIRT_ENABLE_MASK;
+
 	if (sev_guest(vcpu->kvm))
 		sev_vcpu_after_set_cpuid(svm);
 }
-- 
2.43.0