linux-kernel - [PATCH 07/16] KVM: nVMX: Propagate the extended instruction info field

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Message-ID: <20251221040742.29749-8-chang.seok.bae@intel.com>
Date: Sun, 21 Dec 2025 04:07:33 +0000
From: "Chang S. Bae" <chang.seok.bae@...el.com>
To: pbonzini@...hat.com,
	seanjc@...gle.com
Cc: kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	chao.gao@...el.com,
	chang.seok.bae@...el.com
Subject: [PATCH 07/16] KVM: nVMX: Propagate the extended instruction info field

Define the VMCS field offset for the extended instruction information.
Then, propagate the field to nested VMX.

When a virtual CPU enumerates the APX capability, nested VMX should
expose the extended field to address higher register indices.

Link: https://lore.kernel.org/CABgObfa-vqWCenVvvTAoB773AQ+9a1OOT9n5hjqT=zZBDQbb+Q@mail.gmail.com
Suggested-by: Chao Gao <chao.gao@...el.com>
Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
---
Changes since last version:
* Check the availability based on the guest APX capability (Chao)
* Massage the changelog to reflect this fact.
---
 arch/x86/include/asm/vmx.h | 2 ++
 arch/x86/kvm/vmx/nested.c  | 6 ++++++
 arch/x86/kvm/vmx/vmcs12.c  | 1 +
 arch/x86/kvm/vmx/vmcs12.h  | 3 ++-
 4 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
index c85c50019523..ab0684948c56 100644
--- a/arch/x86/include/asm/vmx.h
+++ b/arch/x86/include/asm/vmx.h
@@ -264,6 +264,8 @@ enum vmcs_field {
 	PID_POINTER_TABLE_HIGH		= 0x00002043,
 	GUEST_PHYSICAL_ADDRESS          = 0x00002400,
 	GUEST_PHYSICAL_ADDRESS_HIGH     = 0x00002401,
+	EXTENDED_INSTRUCTION_INFO	= 0x00002406,
+	EXTENDED_INSTRUCTION_INFO_HIGH	= 0x00002407,
 	VMCS_LINK_POINTER               = 0x00002800,
 	VMCS_LINK_POINTER_HIGH          = 0x00002801,
 	GUEST_IA32_DEBUGCTL             = 0x00002802,
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 1e35e1923aec..ce972eeaa6f7 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -4746,6 +4746,12 @@ static void prepare_vmcs12(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
 		vmcs12->vm_exit_intr_info = exit_intr_info;
 		vmcs12->vm_exit_instruction_len = exit_insn_len;
 		vmcs12->vmx_instruction_info = vmcs_read32(VMX_INSTRUCTION_INFO);
+		/*
+		 * The APX enumeration guarantees the presence of the extended
+		 * fields. This CPUID bit alone is sufficient to rely on it.
+		 */
+		if (guest_cpu_cap_has(vcpu, X86_FEATURE_APX))
+			vmcs12->extended_instruction_info = vmcs_read64(EXTENDED_INSTRUCTION_INFO);
 
 		/*
 		 * According to spec, there's no need to store the guest's
diff --git a/arch/x86/kvm/vmx/vmcs12.c b/arch/x86/kvm/vmx/vmcs12.c
index 4233b5ca9461..ea2b690a419e 100644
--- a/arch/x86/kvm/vmx/vmcs12.c
+++ b/arch/x86/kvm/vmx/vmcs12.c
@@ -53,6 +53,7 @@ const unsigned short vmcs12_field_offsets[] = {
 	FIELD64(XSS_EXIT_BITMAP, xss_exit_bitmap),
 	FIELD64(ENCLS_EXITING_BITMAP, encls_exiting_bitmap),
 	FIELD64(GUEST_PHYSICAL_ADDRESS, guest_physical_address),
+	FIELD64(EXTENDED_INSTRUCTION_INFO, extended_instruction_info),
 	FIELD64(VMCS_LINK_POINTER, vmcs_link_pointer),
 	FIELD64(GUEST_IA32_DEBUGCTL, guest_ia32_debugctl),
 	FIELD64(GUEST_IA32_PAT, guest_ia32_pat),
diff --git a/arch/x86/kvm/vmx/vmcs12.h b/arch/x86/kvm/vmx/vmcs12.h
index 4ad6b16525b9..2146e45aaade 100644
--- a/arch/x86/kvm/vmx/vmcs12.h
+++ b/arch/x86/kvm/vmx/vmcs12.h
@@ -71,7 +71,7 @@ struct __packed vmcs12 {
 	u64 pml_address;
 	u64 encls_exiting_bitmap;
 	u64 tsc_multiplier;
-	u64 padding64[1]; /* room for future expansion */
+	u64 extended_instruction_info;
 	/*
 	 * To allow migration of L1 (complete with its L2 guests) between
 	 * machines of different natural widths (32 or 64 bit), we cannot have
@@ -261,6 +261,7 @@ static inline void vmx_check_vmcs12_offsets(void)
 	CHECK_OFFSET(pml_address, 312);
 	CHECK_OFFSET(encls_exiting_bitmap, 320);
 	CHECK_OFFSET(tsc_multiplier, 328);
+	CHECK_OFFSET(extended_instruction_info, 336);
 	CHECK_OFFSET(cr0_guest_host_mask, 344);
 	CHECK_OFFSET(cr4_guest_host_mask, 352);
 	CHECK_OFFSET(cr0_read_shadow, 360);
-- 
2.51.0