[RFC PATCH v2 1/3] KVM: x86: add DSM IRQ forwarding ABI and state

[muliang.shou]

Add the Kconfig knob, request id, per-vCPU state, and userspace ABI
needed to report DSM IRQ forwarding events to userspace.

Signed-off-by: muliang.shou <muliang.shou@xxxxxxxxxxx>
---
 arch/x86/include/asm/kvm_host.h | 17 +++++++++++++++++
 arch/x86/kvm/Kconfig            | 12 ++++++++++++
 include/uapi/linux/kvm.h        | 33 ++++++++++++++++++++++++++++++++-
 3 files changed, 61 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index f14009f25a3b6..7dccfeaee432d 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -131,6 +131,11 @@
 #define KVM_REQ_UPDATE_PROTECTED_GUEST_STATE \
 	KVM_ARCH_REQ_FLAGS(34, KVM_REQUEST_WAIT)
 
+#ifdef CONFIG_KVM_DSM_IRQ_FORWARD
+#define KVM_REQ_DSM_IRQ_FORWARD	\
+	KVM_ARCH_REQ(33)
+#endif
+
 #define CR0_RESERVED_BITS                                               \
 	(~(unsigned long)(X86_CR0_PE | X86_CR0_MP | X86_CR0_EM | X86_CR0_TS \
 			  | X86_CR0_ET | X86_CR0_NE | X86_CR0_WP | X86_CR0_AM \
@@ -1074,6 +1079,14 @@ struct kvm_vcpu_arch {
 	/* AMD MSRC001_0015 Hardware Configuration */
 	u64 msr_hwcr;
 
+#ifdef CONFIG_KVM_DSM_IRQ_FORWARD
+	/* DSM interrupt forwarding */
+	bool dsm_irq_forward_pending;
+	u32 dsm_irq_forward_reg;
+	u32 dsm_irq_forward_val;
+	u32 dsm_irq_forward_dest_id;
+#endif
+
 	/* pv related cpuid info */
 	struct {
 		/*
@@ -1667,6 +1680,10 @@ struct kvm_arch {
 	 * current VM.
 	 */
 	int cpu_dirty_log_size;
+
+#ifdef CONFIG_KVM_DSM_IRQ_FORWARD
+	int dsm_id;
+#endif
 };
 
 struct kvm_vm_stat {
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 801bf9e520db3..bd3a97f115284 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -240,4 +240,16 @@ config KVM_MAX_NR_VCPUS
 	  the memory footprint of each KVM guest, regardless of how many vCPUs are
 	  created for a given VM.
 
+config KVM_DSM_IRQ_FORWARD
+	bool "KVM DSM interrupt forwarding support"
+	depends on KVM && KVM_INTEL
+	default n
+	help
+	  Provide support for interrupt forwarding in distributed KVM.
+	  When enabled, guest ICR/ICR2 writes are intercepted and
+	  forwarded to userspace via KVM_EXIT_DSM_SEND_IRQ exit,
+	  allowing cross-node IPI delivery in a distributed KVM setup.
+	  This feature can be used independently of the full DSM memory
+	  coherence framework.
+
 endif # VIRTUALIZATION
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 6c8afa2047bf3..75a11e72e232e 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -194,6 +194,17 @@ struct kvm_exit_snp_req_certs {
 #define KVM_EXIT_ARM_LDST64B      42
 #define KVM_EXIT_SNP_REQ_CERTS    43
 
+#ifdef CONFIG_KVM_DSM_IRQ_FORWARD
+/* DSM exit reason: distributed APIC region access */
+#define KVM_EXIT_DAPIC            44
+/* DSM exit reason: IPI forwarding to userspace */
+#define KVM_EXIT_DSM_SEND_IRQ     45
+/* DSM exit reason: X2APIC ICR write forwarding to userspace */
+#define KVM_EXIT_DSM_X2_ICR       46
+/* DSM exit reason: APIC base MSR write forwarding to userspace */
+#define KVM_EXIT_DSM_APIC_BASE    47
+#endif
+
 /* For KVM_EXIT_INTERNAL_ERROR */
 /* Emulate instruction failed. */
 #define KVM_INTERNAL_ERROR_EMULATION	1
@@ -243,7 +254,27 @@ struct kvm_run {
 	__u64 psw_addr; /* psw lower half */
 #endif
 	union {
-		/* KVM_EXIT_UNKNOWN */
+#ifdef CONFIG_KVM_DSM_IRQ_FORWARD
+		/* DSM IPI forwarding data (KVM_EXIT_DSM_SEND_IRQ) */
+		struct {
+			__u32 id;
+			__u32 val;
+			__u32 val2;
+			__u32 dest_id;
+		} lapic_irq;
+		/* DSM X2APIC write data (KVM_EXIT_DSM_X2APIC) */
+		struct {
+			__u32 id;
+			__u64 data;
+		} x2apic;
+		/* DSM APIC base write data (KVM_EXIT_DSM_APIC_BASE) */
+		struct {
+			__u32 id;
+			bool host;
+			__u32 index;
+			__u64 data;
+		} x2msr_base;
+#endif
 		struct {
 			__u64 hardware_exit_reason;
 		} hw;
-- 
2.43.0