And I think it's in this patch that you missed a conversion to the alias, in the
prototype for check_memory_region_flags() (looks like it gets fixed up later in
the series).

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 0f81bf0407be..8765b334477d 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c

@@ -1466,7 +1466,7 @@ static void kvm_replace_memslot(struct kvm *kvm,
        }
 }

-static int check_memory_region_flags(const struct kvm_userspace_memory_region *mem)
+static int check_memory_region_flags(const struct kvm_user_mem_region *mem)
 {
        u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;

@@ -4514,6 +4514,33 @@ static int kvm_vm_ioctl_get_stats_fd(struct kvm *kvm)
        return fd;
 }

+#define SANITY_CHECK_MEM_REGION_FIELD(field)                                   \
+do {                                                                           \
+       BUILD_BUG_ON(offsetof(struct kvm_user_mem_region, field) !=             \
+                    offsetof(struct kvm_userspace_memory_region, field));      \
+       BUILD_BUG_ON(sizeof_field(struct kvm_user_mem_region, field) !=         \
+                    sizeof_field(struct kvm_userspace_memory_region, field));  \
+} while (0)
+
+#define SANITY_CHECK_MEM_REGION_EXT_FIELD(field)                                       \
+do {                                                                                   \
+       BUILD_BUG_ON(offsetof(struct kvm_user_mem_region, field) !=                     \
+                    offsetof(struct kvm_userspace_memory_region_ext, field));          \
+       BUILD_BUG_ON(sizeof_field(struct kvm_user_mem_region, field) !=                 \
+                    sizeof_field(struct kvm_userspace_memory_region_ext, field));      \
+} while (0)
+
+static void kvm_sanity_check_user_mem_region_alias(void)
+{
+       SANITY_CHECK_MEM_REGION_FIELD(slot);
+       SANITY_CHECK_MEM_REGION_FIELD(flags);
+       SANITY_CHECK_MEM_REGION_FIELD(guest_phys_addr);
+       SANITY_CHECK_MEM_REGION_FIELD(memory_size);
+       SANITY_CHECK_MEM_REGION_FIELD(userspace_addr);
+       SANITY_CHECK_MEM_REGION_EXT_FIELD(private_offset);
+       SANITY_CHECK_MEM_REGION_EXT_FIELD(private_fd);
+}
+
 static long kvm_vm_ioctl(struct file *filp,
                           unsigned int ioctl, unsigned long arg)
 {

@@ -4541,6 +4568,8 @@ static long kvm_vm_ioctl(struct file *filp,
                unsigned long size;
                u32 flags;

+               kvm_sanity_check_user_mem_region_alias();
+
                memset(&mem, 0, sizeof(mem));

                r = -EFAULT;

quoted

+struct kvm_user_mem_region {
+	__u32 slot;
+	__u32 flags;
+	__u64 guest_phys_addr;
+	__u64 memory_size;
+	__u64 userspace_addr;
+	__u64 private_offset;
+	__u32 private_fd;
+	__u32 pad1;
+	__u64 pad2[14];
+};
+#endif
+
 /*
  * The bit 0 ~ bit 15 of kvm_memory_region::flags are visible for userspace,
  * other bits are reserved for kvm internal use which are defined in

@@ -110,6 +133,7 @@ struct kvm_userspace_memory_region {
  */
 #define KVM_MEM_LOG_DIRTY_PAGES	(1UL << 0)
 #define KVM_MEM_READONLY	(1UL << 1)
+#define KVM_MEM_PRIVATE		(1UL << 2)

Hmm, KVM_MEM_PRIVATE is technically wrong now that a "private" memslot maps private
and/or shared memory.  Strictly speaking, we don't actually need a new flag.  Valid
file descriptors must be >=0, so the logic for specifying a memslot that can be
converted between private and shared could be that "(int)private_fd < 0" means
"not convertible", i.e. derive the flag from private_fd.