KVM: Make support for kvm_arch_vcpu_async_ioctl() mandatory

Implement kvm_arch_vcpu_async_ioctl() "natively" in x86 and arm64 instead
of relying on an #ifdef'd stub, and drop HAVE_KVM_VCPU_ASYNC_IOCTL in
anticipation of using the API on x86.  Once x86 uses the API, providing a
stub for one architecture and having all other architectures opt-in
requires more code than simply implementing the API in the lone holdout.

Eliminating the Kconfig will also reduce churn if the API is renamed in
the future (spoiler alert).

No functional change intended.

Acked-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Reviewed-by: Yan Zhao <yan.y.zhao@intel.com>
Tested-by: Yan Zhao <yan.y.zhao@intel.com>
Tested-by: Kai Huang <kai.huang@intel.com>
Link: https://patch.msgid.link/20251030200951.3402865-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

arch/arm64/kvm/arm.c

@@ -1835,6 +1835,12 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 	return r;
 }
 
+long kvm_arch_vcpu_async_ioctl(struct file *filp, unsigned int ioctl,
+			       unsigned long arg)
+{
+	return -ENOIOCTLCMD;
+}
+
 void kvm_arch_sync_dirty_log(struct kvm *kvm, struct kvm_memory_slot *memslot)
 {
 

arch/loongarch/kvm/Kconfig

@@ -25,7 +25,6 @@ config KVM
 	select HAVE_KVM_IRQCHIP
 	select HAVE_KVM_MSI
 	select HAVE_KVM_READONLY_MEM
-	select HAVE_KVM_VCPU_ASYNC_IOCTL
 	select KVM_COMMON
 	select KVM_GENERIC_DIRTYLOG_READ_PROTECT
 	select KVM_GENERIC_HARDWARE_ENABLING

arch/mips/kvm/Kconfig

@@ -22,7 +22,6 @@ config KVM
 	select EXPORT_UASM
 	select KVM_COMMON
 	select KVM_GENERIC_DIRTYLOG_READ_PROTECT
-	select HAVE_KVM_VCPU_ASYNC_IOCTL
 	select KVM_MMIO
 	select KVM_GENERIC_MMU_NOTIFIER
 	select KVM_GENERIC_HARDWARE_ENABLING

arch/powerpc/kvm/Kconfig

@@ -20,7 +20,6 @@ if VIRTUALIZATION
 config KVM
 	bool
 	select KVM_COMMON
-	select HAVE_KVM_VCPU_ASYNC_IOCTL
 	select KVM_VFIO
 	select HAVE_KVM_IRQ_BYPASS
 

arch/riscv/kvm/Kconfig

@@ -23,7 +23,6 @@ config KVM
 	select HAVE_KVM_IRQCHIP
 	select HAVE_KVM_IRQ_ROUTING
 	select HAVE_KVM_MSI
-	select HAVE_KVM_VCPU_ASYNC_IOCTL
 	select HAVE_KVM_READONLY_MEM
 	select HAVE_KVM_DIRTY_RING_ACQ_REL
 	select KVM_COMMON

arch/s390/kvm/Kconfig

@@ -20,7 +20,6 @@ config KVM
 	def_tristate y
 	prompt "Kernel-based Virtual Machine (KVM) support"
 	select HAVE_KVM_CPU_RELAX_INTERCEPT
-	select HAVE_KVM_VCPU_ASYNC_IOCTL
 	select KVM_ASYNC_PF
 	select KVM_ASYNC_PF_SYNC
 	select KVM_COMMON

arch/x86/kvm/x86.c

@@ -7240,6 +7240,12 @@ static int kvm_vm_ioctl_set_clock(struct kvm *kvm, void __user *argp)
 	return 0;
 }
 
+long kvm_arch_vcpu_async_ioctl(struct file *filp, unsigned int ioctl,
+			       unsigned long arg)
+{
+	return -ENOIOCTLCMD;
+}
+
 int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
 {
 	struct kvm *kvm = filp->private_data;

include/linux/kvm_host.h

@@ -2437,18 +2437,8 @@ static inline bool kvm_arch_no_poll(struct kvm_vcpu *vcpu)
 }
 #endif /* CONFIG_HAVE_KVM_NO_POLL */
 
-#ifdef CONFIG_HAVE_KVM_VCPU_ASYNC_IOCTL
 long kvm_arch_vcpu_async_ioctl(struct file *filp,
 			       unsigned int ioctl, unsigned long arg);
-#else
-static inline long kvm_arch_vcpu_async_ioctl(struct file *filp,
-					     unsigned int ioctl,
-					     unsigned long arg)
-{
-	return -ENOIOCTLCMD;
-}
-#endif /* CONFIG_HAVE_KVM_VCPU_ASYNC_IOCTL */
-
 void kvm_arch_guest_memory_reclaimed(struct kvm *kvm);
 
 #ifdef CONFIG_HAVE_KVM_VCPU_RUN_PID_CHANGE

virt/kvm/Kconfig

@@ -78,9 +78,6 @@ config HAVE_KVM_IRQ_BYPASS
        tristate
        select IRQ_BYPASS_MANAGER
 
-config HAVE_KVM_VCPU_ASYNC_IOCTL
-       bool
-
 config HAVE_KVM_VCPU_RUN_PID_CHANGE
        bool