Re: [PATCH 01/22] KVM: x86: Drop unnecessary and confusing KVM_X86_OP_NULL macro

[Paolo Bonzini <pbonzini@redhat.com>]

On 1/28/22 01:51, Sean Christopherson wrote:
> Drop KVM_X86_OP_NULL, which is superfluous and confusing.  The macro is
> just a "pass-through" to KVM_X86_OP; it was added with the intent of
> actually using it in the future, but that obviously never happened.  The
> name is confusing because its intended use was to provide a way for
> vendor implementations to specify a NULL pointer, and even if it were
> used, wouldn't necessarily be synonymous with declaring a kvm_x86_op as
> DEFINE_STATIC_CALL_NULL.
> 
> Lastly, actually using KVM_X86_OP_NULL as intended isn't a maintanable
> approach, e.g. bleeds vendor details into common x86 code, and would
> either be prone to bit rot or would require modifying common x86 code
> when modifying a vendor implementation.

I have some patches that redefine KVM_X86_OP_NULL as "must be used with 
static_call_cond".  That's a more interesting definition, as it can be 
used to WARN if KVM_X86_OP is used with a NULL function pointer.

Paolo

> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>   arch/x86/include/asm/kvm-x86-ops.h | 76 ++++++++++++++----------------
>   arch/x86/include/asm/kvm_host.h    |  2 -
>   arch/x86/kvm/x86.c                 |  1 -
>   3 files changed, 35 insertions(+), 44 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
> index 631d5040b31e..e07151b2d1f6 100644
> --- a/arch/x86/include/asm/kvm-x86-ops.h
> +++ b/arch/x86/include/asm/kvm-x86-ops.h
> @@ -1,25 +1,20 @@
>   /* SPDX-License-Identifier: GPL-2.0 */
> -#if !defined(KVM_X86_OP) || !defined(KVM_X86_OP_NULL)
> +#ifndef KVM_X86_OP
>   BUILD_BUG_ON(1)
>   #endif
>   
>   /*
> - * KVM_X86_OP() and KVM_X86_OP_NULL() are used to help generate
> - * "static_call()"s. They are also intended for use when defining
> - * the vmx/svm kvm_x86_ops. KVM_X86_OP() can be used for those
> - * functions that follow the [svm|vmx]_func_name convention.
> - * KVM_X86_OP_NULL() can leave a NULL definition for the
> - * case where there is no definition or a function name that
> - * doesn't match the typical naming convention is supplied.
> + * Invoke KVM_X86_OP() on all functions in struct kvm_x86_ops, e.g. to generate
> + * static_call declarations, definitions and updates.
>    */
> -KVM_X86_OP_NULL(hardware_enable)
> -KVM_X86_OP_NULL(hardware_disable)
> -KVM_X86_OP_NULL(hardware_unsetup)
> -KVM_X86_OP_NULL(cpu_has_accelerated_tpr)
> +KVM_X86_OP(hardware_enable)
> +KVM_X86_OP(hardware_disable)
> +KVM_X86_OP(hardware_unsetup)
> +KVM_X86_OP(cpu_has_accelerated_tpr)
>   KVM_X86_OP(has_emulated_msr)
>   KVM_X86_OP(vcpu_after_set_cpuid)
>   KVM_X86_OP(vm_init)
> -KVM_X86_OP_NULL(vm_destroy)
> +KVM_X86_OP(vm_destroy)
>   KVM_X86_OP(vcpu_create)
>   KVM_X86_OP(vcpu_free)
>   KVM_X86_OP(vcpu_reset)
> @@ -33,9 +28,9 @@ KVM_X86_OP(get_segment_base)
>   KVM_X86_OP(get_segment)
>   KVM_X86_OP(get_cpl)
>   KVM_X86_OP(set_segment)
> -KVM_X86_OP_NULL(get_cs_db_l_bits)
> +KVM_X86_OP(get_cs_db_l_bits)
>   KVM_X86_OP(set_cr0)
> -KVM_X86_OP_NULL(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)
> @@ -51,15 +46,15 @@ KVM_X86_OP(set_rflags)
>   KVM_X86_OP(get_if_flag)
>   KVM_X86_OP(tlb_flush_all)
>   KVM_X86_OP(tlb_flush_current)
> -KVM_X86_OP_NULL(tlb_remote_flush)
> -KVM_X86_OP_NULL(tlb_remote_flush_with_range)
> +KVM_X86_OP(tlb_remote_flush)
> +KVM_X86_OP(tlb_remote_flush_with_range)
>   KVM_X86_OP(tlb_flush_gva)
>   KVM_X86_OP(tlb_flush_guest)
>   KVM_X86_OP(vcpu_pre_run)
>   KVM_X86_OP(run)
> -KVM_X86_OP_NULL(handle_exit)
> -KVM_X86_OP_NULL(skip_emulated_instruction)
> -KVM_X86_OP_NULL(update_emulated_instruction)
> +KVM_X86_OP(handle_exit)
> +KVM_X86_OP(skip_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)
> @@ -78,17 +73,17 @@ KVM_X86_OP(check_apicv_inhibit_reasons)
>   KVM_X86_OP(refresh_apicv_exec_ctrl)
>   KVM_X86_OP(hwapic_irr_update)
>   KVM_X86_OP(hwapic_isr_update)
> -KVM_X86_OP_NULL(guest_apic_has_interrupt)
> +KVM_X86_OP(guest_apic_has_interrupt)
>   KVM_X86_OP(load_eoi_exitmap)
>   KVM_X86_OP(set_virtual_apic_mode)
> -KVM_X86_OP_NULL(set_apic_access_page_addr)
> +KVM_X86_OP(set_apic_access_page_addr)
>   KVM_X86_OP(deliver_posted_interrupt)
> -KVM_X86_OP_NULL(sync_pir_to_irr)
> +KVM_X86_OP(sync_pir_to_irr)
>   KVM_X86_OP(set_tss_addr)
>   KVM_X86_OP(set_identity_map_addr)
>   KVM_X86_OP(get_mt_mask)
>   KVM_X86_OP(load_mmu_pgd)
> -KVM_X86_OP_NULL(has_wbinvd_exit)
> +KVM_X86_OP(has_wbinvd_exit)
>   KVM_X86_OP(get_l2_tsc_offset)
>   KVM_X86_OP(get_l2_tsc_multiplier)
>   KVM_X86_OP(write_tsc_offset)
> @@ -96,32 +91,31 @@ KVM_X86_OP(write_tsc_multiplier)
>   KVM_X86_OP(get_exit_info)
>   KVM_X86_OP(check_intercept)
>   KVM_X86_OP(handle_exit_irqoff)
> -KVM_X86_OP_NULL(request_immediate_exit)
> +KVM_X86_OP(request_immediate_exit)
>   KVM_X86_OP(sched_in)
> -KVM_X86_OP_NULL(update_cpu_dirty_logging)
> -KVM_X86_OP_NULL(vcpu_blocking)
> -KVM_X86_OP_NULL(vcpu_unblocking)
> -KVM_X86_OP_NULL(update_pi_irte)
> -KVM_X86_OP_NULL(start_assignment)
> -KVM_X86_OP_NULL(apicv_post_state_restore)
> -KVM_X86_OP_NULL(dy_apicv_has_pending_interrupt)
> -KVM_X86_OP_NULL(set_hv_timer)
> -KVM_X86_OP_NULL(cancel_hv_timer)
> +KVM_X86_OP(update_cpu_dirty_logging)
> +KVM_X86_OP(vcpu_blocking)
> +KVM_X86_OP(vcpu_unblocking)
> +KVM_X86_OP(update_pi_irte)
> +KVM_X86_OP(start_assignment)
> +KVM_X86_OP(apicv_post_state_restore)
> +KVM_X86_OP(dy_apicv_has_pending_interrupt)
> +KVM_X86_OP(set_hv_timer)
> +KVM_X86_OP(cancel_hv_timer)
>   KVM_X86_OP(setup_mce)
>   KVM_X86_OP(smi_allowed)
>   KVM_X86_OP(enter_smm)
>   KVM_X86_OP(leave_smm)
>   KVM_X86_OP(enable_smi_window)
> -KVM_X86_OP_NULL(mem_enc_op)
> -KVM_X86_OP_NULL(mem_enc_reg_region)
> -KVM_X86_OP_NULL(mem_enc_unreg_region)
> +KVM_X86_OP(mem_enc_op)
> +KVM_X86_OP(mem_enc_reg_region)
> +KVM_X86_OP(mem_enc_unreg_region)
>   KVM_X86_OP(get_msr_feature)
>   KVM_X86_OP(can_emulate_instruction)
>   KVM_X86_OP(apic_init_signal_blocked)
> -KVM_X86_OP_NULL(enable_direct_tlbflush)
> -KVM_X86_OP_NULL(migrate_timers)
> +KVM_X86_OP(enable_direct_tlbflush)
> +KVM_X86_OP(migrate_timers)
>   KVM_X86_OP(msr_filter_changed)
> -KVM_X86_OP_NULL(complete_emulated_msr)
> +KVM_X86_OP(complete_emulated_msr)
>   
>   #undef KVM_X86_OP
> -#undef KVM_X86_OP_NULL
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index b2c3721b1c98..756806d2e801 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1538,14 +1538,12 @@ 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_NULL KVM_X86_OP
>   #include <asm/kvm-x86-ops.h>
>   
>   static inline void kvm_ops_static_call_update(void)
>   {
>   #define KVM_X86_OP(func) \
>   	static_call_update(kvm_x86_##func, kvm_x86_ops.func);
> -#define KVM_X86_OP_NULL KVM_X86_OP
>   #include <asm/kvm-x86-ops.h>
>   }
>   
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 8033eca6f3a1..ebab514ec82a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -129,7 +129,6 @@ EXPORT_SYMBOL_GPL(kvm_x86_ops);
>   #define KVM_X86_OP(func)					     \
>   	DEFINE_STATIC_CALL_NULL(kvm_x86_##func,			     \
>   				*(((struct kvm_x86_ops *)0)->func));
> -#define KVM_X86_OP_NULL 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);