KVM: Open code kvm_set_memory_region() into its sole caller (ioctl() API)

Open code kvm_set_memory_region() into its sole caller in preparation for
adding a dedicated API for setting internal memslots.

Oppurtunistically use the fancy new guard(mutex) to avoid a local 'r'
variable.

Cc: Tao Su <tao1.su@linux.intel.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Acked-by: Christoph Schlameuss <schlameuss@linux.ibm.com>
Link: https://lore.kernel.org/r/20250111002022.1230573-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: sean-jc

include/linux/kvm_host.h

@@ -1192,8 +1192,6 @@ enum kvm_mr_change {
 	KVM_MR_FLAGS_ONLY,
 };
 
-int kvm_set_memory_region(struct kvm *kvm,
-			  const struct kvm_userspace_memory_region2 *mem);
 int __kvm_set_memory_region(struct kvm *kvm,
 			    const struct kvm_userspace_memory_region2 *mem);
 void kvm_arch_free_memslot(struct kvm *kvm, struct kvm_memory_slot *slot);

virt/kvm/kvm_main.c

@@ -2058,25 +2058,14 @@ int __kvm_set_memory_region(struct kvm *kvm,
 }
 EXPORT_SYMBOL_GPL(__kvm_set_memory_region);
 
-int kvm_set_memory_region(struct kvm *kvm,
-			  const struct kvm_userspace_memory_region2 *mem)
-{
-	int r;
-
-	mutex_lock(&kvm->slots_lock);
-	r = __kvm_set_memory_region(kvm, mem);
-	mutex_unlock(&kvm->slots_lock);
-	return r;
-}
-EXPORT_SYMBOL_GPL(kvm_set_memory_region);
-
 static int kvm_vm_ioctl_set_memory_region(struct kvm *kvm,
 					  struct kvm_userspace_memory_region2 *mem)
 {
 	if ((u16)mem->slot >= KVM_USER_MEM_SLOTS)
 		return -EINVAL;
 
-	return kvm_set_memory_region(kvm, mem);
+	guard(mutex)(&kvm->slots_lock);
+	return __kvm_set_memory_region(kvm, mem);
 }
 
 #ifndef CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT