[RFC PATCH 08/46] KVM: x86: Add x86 vCPU LUO preservation ABI and register helpers

[Pasha Tatashin <pasha.tatashin@soleen.com>]

Add struct kvm_vcpu_arch_ser in include/linux/kho/abi/kvm_x86.h
and export x86 register and MSR access helpers for LUO state save/restore.

Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
---
 arch/x86/kvm/cpuid.c            |  4 +-
 arch/x86/kvm/cpuid.h            |  1 +
 arch/x86/kvm/msrs.c             | 15 ++++++
 arch/x86/kvm/msrs.h             |  2 +
 arch/x86/kvm/regs.c             |  8 ++--
 arch/x86/kvm/regs.h             |  4 ++
 arch/x86/kvm/x86.c              |  8 ++--
 arch/x86/kvm/x86.h              |  4 ++
 include/linux/kho/abi/kvm_x86.h | 84 +++++++++++++++++++++++++++++++++
 9 files changed, 120 insertions(+), 10 deletions(-)
 create mode 100644 include/linux/kho/abi/kvm_x86.h

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 851f151efb35..5aba16e0610b 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -507,8 +507,8 @@ u64 kvm_vcpu_reserved_gpa_bits_raw(struct kvm_vcpu *vcpu)
 	return rsvd_bits(cpuid_maxphyaddr(vcpu), 63);
 }
 
-static int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2,
-                        int nent)
+int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2,
+		  int nent)
 {
 	u32 vcpu_caps[NR_KVM_CPU_CAPS];
 	int r;
diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index 8d863f45585d..e5ec112d39cc 100644
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -21,6 +21,7 @@ static inline void kvm_finalize_cpu_caps(void)
 }
 
 void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu);
+int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2, int nent);
 struct kvm_cpuid_entry2 *kvm_find_cpuid_entry2(struct kvm_cpuid_entry2 *entries,
 					       int nent, u32 function, u64 index);
 /*
diff --git a/arch/x86/kvm/msrs.c b/arch/x86/kvm/msrs.c
index dd3bb04878ca..ae849e0b7d14 100644
--- a/arch/x86/kvm/msrs.c
+++ b/arch/x86/kvm/msrs.c
@@ -339,6 +339,21 @@ static u32 msr_based_features[ARRAY_SIZE(msr_based_features_all_except_vmx) +
 			      (KVM_LAST_EMULATED_VMX_MSR - KVM_FIRST_EMULATED_VMX_MSR + 1)];
 static unsigned int num_msr_based_features;
 
+unsigned int kvm_num_msrs_to_save(void)
+{
+	return num_msrs_to_save + num_emulated_msrs;
+}
+
+u32 kvm_get_msr_to_save_index(unsigned int i)
+{
+	if (i < num_msrs_to_save)
+		return msrs_to_save[i];
+	i -= num_msrs_to_save;
+	if (i < num_emulated_msrs)
+		return emulated_msrs[i];
+	return 0;
+}
+
 int kvm_get_msr_index_list(struct kvm_msr_list __user *user_msr_list)
 {
 	struct kvm_msr_list msr_list;
diff --git a/arch/x86/kvm/msrs.h b/arch/x86/kvm/msrs.h
index 7cc182a15b3b..3a5e39041d99 100644
--- a/arch/x86/kvm/msrs.h
+++ b/arch/x86/kvm/msrs.h
@@ -65,6 +65,8 @@ int __kvm_emulate_msr_read(struct kvm_vcpu *vcpu, u32 index, u64 *data);
 int __kvm_emulate_msr_write(struct kvm_vcpu *vcpu, u32 index, u64 data);
 int kvm_msr_read(struct kvm_vcpu *vcpu, u32 index, u64 *data);
 int kvm_msr_write(struct kvm_vcpu *vcpu, u32 index, u64 data);
+unsigned int kvm_num_msrs_to_save(void);
+u32 kvm_get_msr_to_save_index(unsigned int i);
 int kvm_emulate_rdmsr(struct kvm_vcpu *vcpu);
 int kvm_emulate_rdmsr_imm(struct kvm_vcpu *vcpu, u32 msr, int reg);
 int kvm_emulate_wrmsr(struct kvm_vcpu *vcpu);
diff --git a/arch/x86/kvm/regs.c b/arch/x86/kvm/regs.c
index 8f66438989e4..02f041c355cc 100644
--- a/arch/x86/kvm/regs.c
+++ b/arch/x86/kvm/regs.c
@@ -51,7 +51,7 @@ void kvm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
 }
 EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_set_rflags);
 
-static void __get_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
+void __get_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
 {
 	if (vcpu->arch.emulate_regs_need_sync_to_vcpu) {
 		/*
@@ -99,7 +99,7 @@ int kvm_arch_vcpu_ioctl_get_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
 	return 0;
 }
 
-static void __set_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
+void __set_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
 {
 	vcpu->arch.emulate_regs_need_sync_from_vcpu = true;
 	vcpu->arch.emulate_regs_need_sync_to_vcpu = false;
@@ -498,7 +498,7 @@ static void __get_sregs_common(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs)
 	sregs->apic_base = vcpu->arch.apic_base;
 }
 
-static void __get_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs)
+void __get_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs)
 {
 	__get_sregs_common(vcpu, sregs);
 
@@ -635,7 +635,7 @@ static int __set_sregs_common(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs,
 	return 0;
 }
 
-static int __set_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs)
+int __set_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs)
 {
 	int pending_vec, max_bits;
 	int mmu_reset_needed = 0;
diff --git a/arch/x86/kvm/regs.h b/arch/x86/kvm/regs.h
index 447f0ec3e63e..40947b1be404 100644
--- a/arch/x86/kvm/regs.h
+++ b/arch/x86/kvm/regs.h
@@ -517,5 +517,9 @@ int kvm_vcpu_ioctl_x86_get_debugregs(struct kvm_vcpu *vcpu,
 int kvm_vcpu_ioctl_x86_set_debugregs(struct kvm_vcpu *vcpu,
 				     struct kvm_debugregs *dbgregs);
 
+void __get_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs);
+void __set_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs);
+void __get_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs);
+int __set_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs);
 
 #endif
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 79468ddfe473..69e0d67a309b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2959,8 +2959,8 @@ void kvm_handle_exception_payload_quirk(struct kvm_vcpu *vcpu)
 		kvm_deliver_exception_payload(vcpu, ex);
 }
 
-static void kvm_vcpu_ioctl_x86_get_vcpu_events(struct kvm_vcpu *vcpu,
-					       struct kvm_vcpu_events *events)
+void kvm_vcpu_ioctl_x86_get_vcpu_events(struct kvm_vcpu *vcpu,
+					struct kvm_vcpu_events *events)
 {
 	struct kvm_queued_exception *ex = kvm_get_exception_to_save(vcpu);
 
@@ -3028,8 +3028,8 @@ static void kvm_vcpu_ioctl_x86_get_vcpu_events(struct kvm_vcpu *vcpu,
 	}
 }
 
-static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
-					      struct kvm_vcpu_events *events)
+int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
+				       struct kvm_vcpu_events *events)
 {
 	if (events->flags & ~(KVM_VCPUEVENT_VALID_NMI_PENDING
 			      | KVM_VCPUEVENT_VALID_SIPI_VECTOR
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 0f5919b092e4..936ee660ccec 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -492,6 +492,10 @@ int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int idt_index,
 		    int reason, bool has_error_code, u32 error_code);
 
 int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr);
+void kvm_vcpu_ioctl_x86_get_vcpu_events(struct kvm_vcpu *vcpu,
+					struct kvm_vcpu_events *events);
+int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
+				       struct kvm_vcpu_events *events);
 int kvm_emulate_xsetbv(struct kvm_vcpu *vcpu);
 int kvm_emulate_rdpmc(struct kvm_vcpu *vcpu);
 
diff --git a/include/linux/kho/abi/kvm_x86.h b/include/linux/kho/abi/kvm_x86.h
new file mode 100644
index 000000000000..316250482db5
--- /dev/null
+++ b/include/linux/kho/abi/kvm_x86.h
@@ -0,0 +1,84 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2026, Google LLC.
+ * Pasha Tatashin <pasha.tatashin@soleen.com>
+ */
+#ifndef _LINUX_KHO_ABI_KVM_X86_H
+#define _LINUX_KHO_ABI_KVM_X86_H
+
+#ifdef CONFIG_X86_64
+
+#include <linux/build_bug.h>
+#include <linux/stddef.h>
+#include <linux/types.h>
+#include <linux/kho/abi/kvm.h>
+#include <uapi/linux/kvm.h>
+#include <uapi/asm/kvm.h>
+
+/**
+ * DOC: x86 KVM Live Update ABI
+ *
+ * x86 KVM uses the ABI defined below for preserving architectural VM and vCPU
+ * state across a kexec reboot using LUO.
+ *
+ * The vCPU-level architectural state contains the compact register sets and
+ * CPUID table for each vCPU.
+ *
+ * All sub-structures (struct kvm_regs, struct kvm_sregs, struct kvm_mp_state,
+ * struct kvm_cpuid_entry2) are uAPI contracts.
+ */
+
+/**
+ * struct kvm_vcpu_arch_ser - Preserved x86 architectural vCPU state in RAM.
+ * @regs:          General-purpose registers (uAPI struct kvm_regs).
+ * @sregs:         Segment and control registers (uAPI struct kvm_sregs).
+ * @mp_state:      Multiprocessor state (uAPI struct kvm_mp_state).
+ * @pad:           Padding to maintain 64-bit alignment after mp_state.
+ * @xcrs:          Extended control registers including XCR0 (uAPI struct kvm_xcrs).
+ * @lapic:         In-kernel local APIC register state (uAPI struct kvm_lapic_state).
+ * @pad_xsave:     Padding that aligns @xsave to 64 bytes; see the static_assert
+ *                 below.  Must be zero.
+ * @xsave:         Extended processor state (uAPI struct kvm_xsave).  This is the
+ *                 only copy of the guest FPU state; there is no kvm_fpu twin.
+ * @events:        vCPU exception, interrupt, NMI and SMI events (uAPI struct kvm_vcpu_events).
+ * @debugregs:     Hardware debug registers DR0-DR7 (uAPI struct kvm_debugregs).
+ * @num_msrs:      Number of valid MSR entries in msrs.
+ * @cpuid_nent:    Number of valid CPUID entries immediately following msrs[num_msrs].
+ * @msrs:          Array of preserved architectural and paravirtual MSR entries,
+ *                 followed by @cpuid_nent struct kvm_cpuid_entry2 entries.
+ */
+struct kvm_vcpu_arch_ser {
+	struct kvm_regs regs;
+	struct kvm_sregs sregs;
+	struct kvm_mp_state mp_state;
+	u32 pad;
+	struct kvm_xcrs xcrs;
+	struct kvm_lapic_state lapic;
+	u8 pad_xsave[40];
+	struct kvm_xsave xsave;
+	struct kvm_vcpu_events events;
+	struct kvm_debugregs debugregs;
+	u32 num_msrs;
+	u32 cpuid_nent;
+	struct kvm_msr_entry msrs[];
+} __packed;
+
+static_assert(offsetof(struct kvm_vcpu_arch_ser, msrs) % sizeof(u64) == 0,
+	      "msrs must be 64-bit aligned");
+
+/*
+ * @xsave must be a legal XSAVE destination.  The structure is __packed, so
+ * without @pad_xsave the member lands at offset 1880, which is not even
+ * 16-byte aligned, and the XSAVE/XRSTOR family faults on anything less than
+ * 64.  The allocation itself is fine: kho_alloc_preserve() returns a folio
+ * address, so the base is page aligned.
+ *
+ * If this assert fires, a member above @xsave changed size; adjust
+ * @pad_xsave rather than deleting the assert.
+ */
+static_assert(offsetof(struct kvm_vcpu_arch_ser, xsave) % 64 == 0,
+	      "xsave must be 64-byte aligned to be XSAVE-able in place");
+
+#endif /* CONFIG_X86_64 */
+
+#endif /* _LINUX_KHO_ABI_KVM_X86_H */
-- 
2.55.0.1082.g2b9226bbc0-goog