On Thu, Sep 15, 2022 at 10:29:13PM +0800, Chao Peng wrote:

Expose KVM_MEM_PRIVATE and memslot fields private_fd/offset to
userspace. KVM will register/unregister private memslot to fd-based
memory backing store and response to invalidation event from
inaccessible_notifier to zap the existing memory mappings in the
secondary page table.

Whether KVM_MEM_PRIVATE is actually exposed to userspace is determined
by architecture code which can turn on it by overriding the default
kvm_arch_has_private_mem().

A 'kvm' reference is added in memslot structure since in
inaccessible_notifier callback we can only obtain a memslot reference
but 'kvm' is needed to do the zapping.

Co-developed-by: Yu Zhang <redacted>
Signed-off-by: Yu Zhang <redacted>
Signed-off-by: Chao Peng <redacted>

ld: arch/x86/../../virt/kvm/kvm_main.o: in function `kvm_free_memslot':
kvm_main.c:(.text+0x1385): undefined reference to `inaccessible_unregister_notifier'
ld: arch/x86/../../virt/kvm/kvm_main.o: in function `kvm_set_memslot':
kvm_main.c:(.text+0x1b86): undefined reference to `inaccessible_register_notifier'
ld: kvm_main.c:(.text+0x1c85): undefined reference to `inaccessible_unregister_notifier'
ld: arch/x86/kvm/mmu/mmu.o: in function `kvm_faultin_pfn':
mmu.c:(.text+0x1e38): undefined reference to `inaccessible_get_pfn'
ld: arch/x86/kvm/mmu/mmu.o: in function `direct_page_fault':
mmu.c:(.text+0x67ca): undefined reference to `inaccessible_put_pfn'
make: *** [Makefile:1169: vmlinux] Error 1

I attached kernel config for reproduction.

The problem is that CONFIG_MEMFD_CREATE does not get enabled:

mm/Makefile:obj-$(CONFIG_MEMFD_CREATE) += memfd.o memfd_inaccessible.o

BR, Jarkko