KVM: guest_memfd: New hooks and functionality for SEV-SNP and TDX

[Matthew, you're Cc'd here for patches 1 and 3 which touch
 the mm/filemap code.  Since in the meanwhile the KVM side has
 taken a more definitive shape, this time through review/ack is
 welcome! And there is a proper commit message too. - Paolo]

This is the next version of the gmem common API patches,
adding target-independent functionality and hooks that are
needed by SEV-SNP and TDX.

The code in here is mostly taken from two series:

- [PATCH 00/21] TDX/SNP part 1 of n, for 6.9
  https://lore.kernel.org/kvm/20240227232100.478238-1-pbonz...

- [PATCH gmem 0/6] gmem fix-ups and interfaces for populating gmem pages
  https://lore.kernel.org/kvm/20240329212444.395559-1-micha...

1-2: This introduces an AS_INACCESSIBLE flag that prevents unexpected
     accesses to hole-punched gmem pages before invalidation hooks have had
     a chance to make them safely accessible to the host again.

3-9: This introduces an interface for preparing gmem pages either on first
     use or by populating them with user data.

     The latter interface, kvm_gmem_populate(), alternates calls
     to __kvm_gmem_get_pfn() with calls to a user provided callback.
     This implementation simplifies the handling of races and errors,
     by confining filemap rollback and locking in kvm_gmem_populate().
     The function's tasks are otherwise kept to the minimum so that
     it can be used by both SNP and TDX.

10-11: This introduces other hooks needed by SEV-SNP, and is unchanged
       from "[PATCH 00/21] TDX/SNP part 1 of n, for 6.9".

The main changes compared to the previous posting are in patch 9;
both the locking of kvm_gmem_populate() (which now takes the
filemap's invalidate_lock) and the operation of the function
(which now looks up the memslot, but OTOH does not do copy_from_user()
anymore) are pretty new.  I tested the logic slightly by adding a call
to it for sw-protected VMs.

Shout or post fixups if it breaks something for you.

Current state:

- kvm/queue has the SEV_INIT2 and some easy refactorings from
  the TDX series.  Both are expected to move to kvm/next soon.

- I have pushed this already at kvm-coco-queue, but I haven't
  finished the #VE series yet so tomorrow I'll post it and
  update kvm-coco-queue again.

Paolo


Michael Roth (4):
  mm: Introduce AS_INACCESSIBLE for encrypted/confidential memory
  KVM: guest_memfd: Use AS_INACCESSIBLE when creating guest_memfd inode
  KVM: guest_memfd: Add hook for invalidating memory
  KVM: x86: Add gmem hook for determining max NPT mapping level

Paolo Bonzini (7):
  KVM: guest_memfd: pass error up from filemap_grab_folio
  filemap: add FGP_CREAT_ONLY
  KVM: guest_memfd: limit overzealous WARN
  KVM: guest_memfd: Add hook for initializing memory
  KVM: guest_memfd: extract __kvm_gmem_get_pfn()
  KVM: guest_memfd: extract __kvm_gmem_punch_hole()
  KVM: guest_memfd: Add interface for populating gmem pages with user
    data

 arch/x86/include/asm/kvm-x86-ops.h |   3 +
 arch/x86/include/asm/kvm_host.h    |   4 +
 arch/x86/kvm/mmu/mmu.c             |   8 +
 arch/x86/kvm/x86.c                 |  13 ++
 include/linux/kvm_host.h           |  35 +++++
 include/linux/pagemap.h            |   3 +
 mm/filemap.c                       |   4 +
 mm/truncate.c                      |   3 +-
 virt/kvm/Kconfig                   |   8 +
 virt/kvm/guest_memfd.c             | 230 ++++++++++++++++++++++++-----
 10 files changed, 277 insertions(+), 34 deletions(-)

-- 
2.43.0