linux-kernel - [PATCH 1/7] KVM: SVM: Initialize FRED VMCB fields

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Message-ID: <20260129063653.3553076-2-shivansh.dhiman@amd.com>
Date: Thu, 29 Jan 2026 06:36:47 +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 1/7] KVM: SVM: Initialize FRED VMCB fields

From: Neeraj Upadhyay <Neeraj.Upadhyay@....com>

The upcoming AMD FRED (Flexible Return and Event Delivery) feature
introduces several new fields to the VMCB save area. These fields include
FRED-specific stack pointers (fred_rsp[0-3], fred_ssp[1-3]), stack level
tracking (fred_stklvls), and configuration (fred_config).

Ensure that a vCPU starts with a clean and valid FRED state on
capable hardware. Also update the size of save areas of VMCB.

Signed-off-by: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
Co-developed-by: Shivansh Dhiman <shivansh.dhiman@....com>
Signed-off-by: Shivansh Dhiman <shivansh.dhiman@....com>
Reviewed-by: Nikunj A Dadhania <nikunj@....com>
---
 arch/x86/include/asm/svm.h | 33 ++++++++++++++++++++++++++++++---
 arch/x86/kvm/svm/svm.c     | 10 ++++++++++
 2 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
index 17f6c3fedeee..a42ed39aa8fb 100644
--- a/arch/x86/include/asm/svm.h
+++ b/arch/x86/include/asm/svm.h
@@ -165,7 +165,10 @@ struct __attribute__ ((__packed__)) vmcb_control_area {
 	u8 reserved_9[22];
 	u64 allowed_sev_features;	/* Offset 0x138 */
 	u64 guest_sev_features;		/* Offset 0x140 */
-	u8 reserved_10[664];
+	u8 reserved_10[40];
+	u64 exit_int_data;		/* Offset 0x170 */
+	u64 event_inj_data;
+	u8 reserved_11[608];
 	/*
 	 * Offset 0x3e0, 32 bytes reserved
 	 * for use by hypervisor/software.
@@ -360,6 +363,18 @@ struct vmcb_save_area {
 	u64 last_excp_to;
 	u8 reserved_0x298[72];
 	u64 spec_ctrl;		/* Guest version of SPEC_CTRL at 0x2E0 */
+	u8 reserved_0x2e8[448];
+	u64 guest_exit_int_data;        /* GUEST_EXITINTDATA 0x4A8 */
+	u64 guest_event_inj_data;
+	u64 fred_rsp0;
+	u64 fred_rsp1;
+	u64 fred_rsp2;
+	u64 fred_rsp3;
+	u64 fred_stklvls;
+	u64 fred_ssp1;
+	u64 fred_ssp2;
+	u64 fred_ssp3;
+	u64 fred_config;
 } __packed;
 
 /* Save area definition for SEV-ES and SEV-SNP guests */
@@ -472,6 +487,18 @@ struct sev_es_save_area {
 	u8 fpreg_x87[80];
 	u8 fpreg_xmm[256];
 	u8 fpreg_ymm[256];
+	u8 reserved_0x670[568];
+	u64 guest_exit_int_data;        /* GUEST_EXITINTDATA 0x8A8 */
+	u64 guest_event_inj_data;
+	u64 fred_rsp0;
+	u64 fred_rsp1;
+	u64 fred_rsp2;
+	u64 fred_rsp3;
+	u64 fred_stklvls;
+	u64 fred_ssp1;
+	u64 fred_ssp2;
+	u64 fred_ssp3;
+	u64 fred_config;
 } __packed;
 
 struct ghcb_save_area {
@@ -542,9 +569,9 @@ struct vmcb {
 	};
 } __packed;
 
-#define EXPECTED_VMCB_SAVE_AREA_SIZE		744
+#define EXPECTED_VMCB_SAVE_AREA_SIZE		1280
 #define EXPECTED_GHCB_SAVE_AREA_SIZE		1032
-#define EXPECTED_SEV_ES_SAVE_AREA_SIZE		1648
+#define EXPECTED_SEV_ES_SAVE_AREA_SIZE		2304
 #define EXPECTED_VMCB_CONTROL_AREA_SIZE		1024
 #define EXPECTED_GHCB_SIZE			PAGE_SIZE
 
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index f4ccb3e66635..5cec971a1f5a 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1110,6 +1110,16 @@ static void init_vmcb(struct kvm_vcpu *vcpu, bool init_event)
 	save->idtr.base = 0;
 	save->idtr.limit = 0xffff;
 
+	save->fred_rsp0 = 0;
+	save->fred_rsp1 = 0;
+	save->fred_rsp2 = 0;
+	save->fred_rsp3 = 0;
+	save->fred_stklvls = 0;
+	save->fred_ssp1 = 0;
+	save->fred_ssp2 = 0;
+	save->fred_ssp3 = 0;
+	save->fred_config = 0;
+
 	init_sys_seg(&save->ldtr, SEG_TYPE_LDT);
 	init_sys_seg(&save->tr, SEG_TYPE_BUSY_TSS16);
 
-- 
2.43.0