KVM: Unconditionally export KVM_CAP_READONLY_MEM

The idea between capabilities and the KVM_CHECK_EXTENSION ioctl is that
userspace can, at run-time, determine if a feature is supported or not.
This allows KVM to being supporting a new feature with a new kernel
version without any need to update user space.  Unfortunately, since the
definition of KVM_CAP_READONLY_MEM was guarded by #ifdef
__KVM_HAVE_READONLY_MEM, such discovery still required a user space
update.

Therefore, unconditionally export KVM_CAP_READONLY_MEM and change the
in-kernel conditional to rely on __KVM_HAVE_READONLY_MEM.
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/uapi/linux/kvm.h

@@ -738,9 +738,7 @@ struct kvm_ppc_smmu_info {
 #define KVM_CAP_PPC_GET_SMMU_INFO 78
 #define KVM_CAP_S390_COW 79
 #define KVM_CAP_PPC_ALLOC_HTAB 80
-#ifdef __KVM_HAVE_READONLY_MEM
 #define KVM_CAP_READONLY_MEM 81
-#endif
 #define KVM_CAP_IRQFD_RESAMPLE 82
 #define KVM_CAP_PPC_BOOKE_WATCHDOG 83
 #define KVM_CAP_PPC_HTAB_FD 84

virt/kvm/kvm_main.c

@@ -708,7 +708,7 @@ static int check_memory_region_flags(struct kvm_userspace_memory_region *mem)
 {
 	u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
 
-#ifdef KVM_CAP_READONLY_MEM
+#ifdef __KVM_HAVE_READONLY_MEM
 	valid_flags |= KVM_MEM_READONLY;
 #endif