[PATCH v4 04/21] KVM: x86: Extend VCPU registers for EGPRs

["Chang S. Bae" <chang.seok.bae@intel.com>]

Extend the storage to include extended general-purpose registers (EGPRs:
R16-R31) when CONFIG_KVM_APX=y. This option is for VMX only.

Although EGPR state is XSAVE-managed, and thus could be stored in the
guest fpstate, VCPU storage provides a more convenient and efficient
access path for KVM.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Link: https://lore.kernel.org/abL8SW5JS1aV5goa@google.com
---
Dependency: Based on Sean's APX preparatory series
            https://lore.kernel.org/20260409224236.2021562-1-seanjc@google.com/
---
 arch/x86/include/asm/kvm_host.h | 18 ++++++++++++++++++
 arch/x86/kvm/Kconfig            |  4 ++++
 2 files changed, 22 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index a70ed9a6a4fa..76c91efca722 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -189,6 +189,24 @@ enum kvm_reg {
 	VCPU_REGS_R13,
 	VCPU_REGS_R14,
 	VCPU_REGS_R15,
+#endif
+#ifdef CONFIG_KVM_APX
+	VCPU_REGS_R16,
+	VCPU_REGS_R17,
+	VCPU_REGS_R18,
+	VCPU_REGS_R19,
+	VCPU_REGS_R20,
+	VCPU_REGS_R21,
+	VCPU_REGS_R22,
+	VCPU_REGS_R23,
+	VCPU_REGS_R24,
+	VCPU_REGS_R25,
+	VCPU_REGS_R26,
+	VCPU_REGS_R27,
+	VCPU_REGS_R28,
+	VCPU_REGS_R29,
+	VCPU_REGS_R30,
+	VCPU_REGS_R31,
 #endif
 	NR_VCPU_GENERAL_PURPOSE_REGS,
 
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 801bf9e520db..f27e3f2937f0 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -93,10 +93,14 @@ config KVM_SW_PROTECTED_VM
 
 	  If unsure, say "N".
 
+config KVM_APX
+	bool
+
 config KVM_INTEL
 	tristate "KVM for Intel (and compatible) processors support"
 	depends on KVM && IA32_FEAT_CTL
 	select X86_FRED if X86_64
+	select KVM_APX if X86_64
 	help
 	  Provides support for KVM on processors equipped with Intel's VT
 	  extensions, a.k.a. Virtual Machine Extensions (VMX).
-- 
2.51.0