[RFC PATCH v2 4/5] KVM: x86: Remove KVM_X86_OP_OPTIONAL

[Wei Wang <wei.w.wang@intel.com>]

KVM_X86_OP and KVM_X86_OP_OPTIONAL were utilized to define and execute
static_call_update() calls on mandatory and optional hooks, respectively.
Mandatory hooks were invoked via static_call() and necessitated definition
due to the presumption that an undefined hook (i.e., NULL) would cause
static_call() to fail. This assumption no longer holds true as
static_call() has been updated to treat a "NULL" hook as a NOP on x86.
Consequently, the so-called mandatory hooks are no longer required to be
defined, rendering them non-mandatory. This eliminates the need to
differentiate between mandatory and optional hooks, allowing a single
KVM_X86_OP to suffice.

So KVM_X86_OP_OPTIONAL and the WARN_ON() associated with KVM_X86_OP are
removed to simplify usage, and KVM_X86_OP_OPTIONAL_RET0 is renamed to
KVM_X86_OP_RET0, as the term "optional" is now redundant (every hook
can be optional).

Signed-off-by: Wei Wang <wei.w.wang@intel.com>
---
 arch/x86/include/asm/kvm-x86-ops.h | 100 ++++++++++++++---------------
 arch/x86/include/asm/kvm_host.h    |   3 +-
 arch/x86/kvm/x86.c                 |  11 +---
 3 files changed, 52 insertions(+), 62 deletions(-)

diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
index 110d7f29ca9a..306c9820e373 100644
--- a/arch/x86/include/asm/kvm-x86-ops.h
+++ b/arch/x86/include/asm/kvm-x86-ops.h
@@ -1,18 +1,15 @@
 /* SPDX-License-Identifier: GPL-2.0 */
-#if !defined(KVM_X86_OP) || !defined(KVM_X86_OP_OPTIONAL)
+#if !defined(KVM_X86_OP)
 BUILD_BUG_ON(1)
 #endif
 
 /*
- * KVM_X86_OP() and KVM_X86_OP_OPTIONAL() are used to help generate
- * both DECLARE/DEFINE_STATIC_CALL() invocations and
- * "static_call_update()" calls.
- *
- * KVM_X86_OP_OPTIONAL() can be used for those functions that can have
- * a NULL definition, for example if "static_call_cond()" will be used
- * at the call sites.  KVM_X86_OP_OPTIONAL_RET0() can be used likewise
- * to make a definition optional, but in this case the default will
- * be __static_call_return0.
+ * KVM_X86_OP() is used to help generate both DECLARE/DEFINE_STATIC_CALL()
+ * invocations and static_call_update() calls. All the hooks defined can be
+ * optional now, as invocation to an undefined hook (i.e.) has now been treated
+ * as a NOP by static_call().
+ * KVM_X86_OP_RET0() can be used to make an undefined operation be
+ * __static_call_return0.
  */
 KVM_X86_OP(check_processor_compatibility)
 KVM_X86_OP(hardware_enable)
@@ -21,8 +18,8 @@ KVM_X86_OP(hardware_unsetup)
 KVM_X86_OP(has_emulated_msr)
 KVM_X86_OP(vcpu_after_set_cpuid)
 KVM_X86_OP(vm_init)
-KVM_X86_OP_OPTIONAL(vm_destroy)
-KVM_X86_OP_OPTIONAL_RET0(vcpu_precreate)
+KVM_X86_OP(vm_destroy)
+KVM_X86_OP_RET0(vcpu_precreate)
 KVM_X86_OP(vcpu_create)
 KVM_X86_OP(vcpu_free)
 KVM_X86_OP(vcpu_reset)
@@ -39,7 +36,7 @@ KVM_X86_OP(set_segment)
 KVM_X86_OP(get_cs_db_l_bits)
 KVM_X86_OP(is_valid_cr0)
 KVM_X86_OP(set_cr0)
-KVM_X86_OP_OPTIONAL(post_set_cr3)
+KVM_X86_OP(post_set_cr3)
 KVM_X86_OP(is_valid_cr4)
 KVM_X86_OP(set_cr4)
 KVM_X86_OP(set_efer)
@@ -56,8 +53,8 @@ KVM_X86_OP(get_if_flag)
 KVM_X86_OP(flush_tlb_all)
 KVM_X86_OP(flush_tlb_current)
 #if IS_ENABLED(CONFIG_HYPERV)
-KVM_X86_OP_OPTIONAL(flush_remote_tlbs)
-KVM_X86_OP_OPTIONAL(flush_remote_tlbs_range)
+KVM_X86_OP(flush_remote_tlbs)
+KVM_X86_OP(flush_remote_tlbs_range)
 #endif
 KVM_X86_OP(flush_tlb_gva)
 KVM_X86_OP(flush_tlb_guest)
@@ -65,14 +62,14 @@ KVM_X86_OP(vcpu_pre_run)
 KVM_X86_OP(vcpu_run)
 KVM_X86_OP(handle_exit)
 KVM_X86_OP(skip_emulated_instruction)
-KVM_X86_OP_OPTIONAL(update_emulated_instruction)
+KVM_X86_OP(update_emulated_instruction)
 KVM_X86_OP(set_interrupt_shadow)
 KVM_X86_OP(get_interrupt_shadow)
 KVM_X86_OP(patch_hypercall)
 KVM_X86_OP(inject_irq)
 KVM_X86_OP(inject_nmi)
-KVM_X86_OP_OPTIONAL_RET0(is_vnmi_pending)
-KVM_X86_OP_OPTIONAL_RET0(set_vnmi_pending)
+KVM_X86_OP_RET0(is_vnmi_pending)
+KVM_X86_OP_RET0(set_vnmi_pending)
 KVM_X86_OP(inject_exception)
 KVM_X86_OP(cancel_injection)
 KVM_X86_OP(interrupt_allowed)
@@ -81,19 +78,19 @@ KVM_X86_OP(get_nmi_mask)
 KVM_X86_OP(set_nmi_mask)
 KVM_X86_OP(enable_nmi_window)
 KVM_X86_OP(enable_irq_window)
-KVM_X86_OP_OPTIONAL(update_cr8_intercept)
+KVM_X86_OP(update_cr8_intercept)
 KVM_X86_OP(refresh_apicv_exec_ctrl)
-KVM_X86_OP_OPTIONAL(hwapic_irr_update)
-KVM_X86_OP_OPTIONAL(hwapic_isr_update)
-KVM_X86_OP_OPTIONAL_RET0(guest_apic_has_interrupt)
-KVM_X86_OP_OPTIONAL(load_eoi_exitmap)
-KVM_X86_OP_OPTIONAL(set_virtual_apic_mode)
-KVM_X86_OP_OPTIONAL(set_apic_access_page_addr)
+KVM_X86_OP(hwapic_irr_update)
+KVM_X86_OP(hwapic_isr_update)
+KVM_X86_OP_RET0(guest_apic_has_interrupt)
+KVM_X86_OP(load_eoi_exitmap)
+KVM_X86_OP(set_virtual_apic_mode)
+KVM_X86_OP(set_apic_access_page_addr)
 KVM_X86_OP(deliver_interrupt)
-KVM_X86_OP_OPTIONAL(sync_pir_to_irr)
-KVM_X86_OP_OPTIONAL_RET0(set_tss_addr)
-KVM_X86_OP_OPTIONAL_RET0(set_identity_map_addr)
-KVM_X86_OP_OPTIONAL_RET0(get_mt_mask)
+KVM_X86_OP(sync_pir_to_irr)
+KVM_X86_OP_RET0(set_tss_addr)
+KVM_X86_OP_RET0(set_identity_map_addr)
+KVM_X86_OP_RET0(get_mt_mask)
 KVM_X86_OP(load_mmu_pgd)
 KVM_X86_OP(has_wbinvd_exit)
 KVM_X86_OP(get_l2_tsc_offset)
@@ -104,16 +101,16 @@ KVM_X86_OP(get_exit_info)
 KVM_X86_OP(check_intercept)
 KVM_X86_OP(handle_exit_irqoff)
 KVM_X86_OP(sched_in)
-KVM_X86_OP_OPTIONAL(update_cpu_dirty_logging)
-KVM_X86_OP_OPTIONAL(vcpu_blocking)
-KVM_X86_OP_OPTIONAL(vcpu_unblocking)
-KVM_X86_OP_OPTIONAL(pi_update_irte)
-KVM_X86_OP_OPTIONAL(pi_start_assignment)
-KVM_X86_OP_OPTIONAL(apicv_pre_state_restore)
-KVM_X86_OP_OPTIONAL(apicv_post_state_restore)
-KVM_X86_OP_OPTIONAL_RET0(dy_apicv_has_pending_interrupt)
-KVM_X86_OP_OPTIONAL(set_hv_timer)
-KVM_X86_OP_OPTIONAL(cancel_hv_timer)
+KVM_X86_OP(update_cpu_dirty_logging)
+KVM_X86_OP(vcpu_blocking)
+KVM_X86_OP(vcpu_unblocking)
+KVM_X86_OP(pi_update_irte)
+KVM_X86_OP(pi_start_assignment)
+KVM_X86_OP(apicv_pre_state_restore)
+KVM_X86_OP(apicv_post_state_restore)
+KVM_X86_OP_RET0(dy_apicv_has_pending_interrupt)
+KVM_X86_OP(set_hv_timer)
+KVM_X86_OP(cancel_hv_timer)
 KVM_X86_OP(setup_mce)
 #ifdef CONFIG_KVM_SMM
 KVM_X86_OP(smi_allowed)
@@ -121,24 +118,23 @@ KVM_X86_OP(enter_smm)
 KVM_X86_OP(leave_smm)
 KVM_X86_OP(enable_smi_window)
 #endif
-KVM_X86_OP_OPTIONAL(mem_enc_ioctl)
-KVM_X86_OP_OPTIONAL(mem_enc_register_region)
-KVM_X86_OP_OPTIONAL(mem_enc_unregister_region)
-KVM_X86_OP_OPTIONAL(vm_copy_enc_context_from)
-KVM_X86_OP_OPTIONAL(vm_move_enc_context_from)
-KVM_X86_OP_OPTIONAL(guest_memory_reclaimed)
+KVM_X86_OP(mem_enc_ioctl)
+KVM_X86_OP(mem_enc_register_region)
+KVM_X86_OP(mem_enc_unregister_region)
+KVM_X86_OP(vm_copy_enc_context_from)
+KVM_X86_OP(vm_move_enc_context_from)
+KVM_X86_OP(guest_memory_reclaimed)
 KVM_X86_OP(get_msr_feature)
 KVM_X86_OP(check_emulate_instruction)
 KVM_X86_OP(apic_init_signal_blocked)
-KVM_X86_OP_OPTIONAL(enable_l2_tlb_flush)
-KVM_X86_OP_OPTIONAL(migrate_timers)
+KVM_X86_OP(enable_l2_tlb_flush)
+KVM_X86_OP(migrate_timers)
 KVM_X86_OP(msr_filter_changed)
 KVM_X86_OP(complete_emulated_msr)
 KVM_X86_OP(vcpu_deliver_sipi_vector)
-KVM_X86_OP_OPTIONAL_RET0(vcpu_get_apicv_inhibit_reasons);
-KVM_X86_OP_OPTIONAL(get_untagged_addr)
-KVM_X86_OP_OPTIONAL(alloc_apic_backing_page)
+KVM_X86_OP_RET0(vcpu_get_apicv_inhibit_reasons);
+KVM_X86_OP(get_untagged_addr)
+KVM_X86_OP(alloc_apic_backing_page)
 
 #undef KVM_X86_OP
-#undef KVM_X86_OP_OPTIONAL
-#undef KVM_X86_OP_OPTIONAL_RET0
+#undef KVM_X86_OP_RET0
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 3a2e42bb6969..647e7ec7c381 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1857,8 +1857,7 @@ extern struct kvm_x86_ops kvm_x86_ops;
 
 #define KVM_X86_OP(func) \
 	DECLARE_STATIC_CALL(kvm_x86_##func, *(((struct kvm_x86_ops *)0)->func));
-#define KVM_X86_OP_OPTIONAL KVM_X86_OP
-#define KVM_X86_OP_OPTIONAL_RET0 KVM_X86_OP
+#define KVM_X86_OP_RET0 KVM_X86_OP
 #include <asm/kvm-x86-ops.h>
 
 int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 2467e053cb35..58c13bf68057 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -138,8 +138,7 @@ struct kvm_x86_ops kvm_x86_ops __read_mostly;
 #define KVM_X86_OP(func)					     \
 	DEFINE_STATIC_CALL_NULL(kvm_x86_##func,			     \
 				*(((struct kvm_x86_ops *)0)->func));
-#define KVM_X86_OP_OPTIONAL KVM_X86_OP
-#define KVM_X86_OP_OPTIONAL_RET0 KVM_X86_OP
+#define KVM_X86_OP_RET0 KVM_X86_OP
 #include <asm/kvm-x86-ops.h>
 EXPORT_STATIC_CALL_GPL(kvm_x86_get_cs_db_l_bits);
 EXPORT_STATIC_CALL_GPL(kvm_x86_cache_reg);
@@ -9656,16 +9655,12 @@ static inline void kvm_ops_update(struct kvm_x86_init_ops *ops)
 {
 	memcpy(&kvm_x86_ops, ops->runtime_ops, sizeof(kvm_x86_ops));
 
-#define __KVM_X86_OP(func) \
-	static_call_update(kvm_x86_##func, kvm_x86_ops.func);
 #define KVM_X86_OP(func) \
-	WARN_ON(!kvm_x86_ops.func); __KVM_X86_OP(func)
-#define KVM_X86_OP_OPTIONAL __KVM_X86_OP
-#define KVM_X86_OP_OPTIONAL_RET0(func) \
+	static_call_update(kvm_x86_##func, kvm_x86_ops.func);
+#define KVM_X86_OP_RET0(func) \
 	static_call_update(kvm_x86_##func, (void *)kvm_x86_ops.func ? : \
 					   (void *)__static_call_return0);
 #include <asm/kvm-x86-ops.h>
-#undef __KVM_X86_OP
 
 	kvm_pmu_ops_update(ops->pmu_ops);
 }
-- 
2.27.0