[PATCH v10 00/16] KVM: Mapping guest_memfd backed memory at the host for software protected VMs

[Fuad Tabba <tabba@google.com>]

Main changes since v9 [1]:
- Dropped best-effort validation that the userspace memory address range
  matches the shared memory backed by guest_memfd
- Rework handling faults for shared guest_memfd memory in arm64
- Track in the memslot whether it's backed by guest_memfd with shared
  memory support
- Various fixes based on feedback from v9
- Rebase on Linux 6.15

The purpose of this series is to allow mapping guest_memfd backed memory
at the host. This support enables VMMs like Firecracker to run guests
backed completely by guest_memfd [2]. Combined with Patrick's series for
direct map removal in guest_memfd [3], this would allow running VMs that
offer additional hardening against Spectre-like transient execution
attacks.

This series will also serve as a base for _restricted_ mmap() support
for guest_memfd backed memory at the host for CoCos that allow sharing
guest memory in-place with the host [4].

Patches 1 to 7 are mainly about decoupling the concept of guest memory
being private vs guest memory being backed by guest_memfd. They are
mostly refactoring and renaming.

Patches 8 and 9 add support for in-place shared memory, as well as the
ability to map it by the host as long as it is shared, gated by a new
configuration option, toggled by a new flag, and advertised to userspace
by a new capability (introduced in patch 15).

Patches 10 to 14 add x86 and arm64 support for in-place shared memory.

Patch 15 introduces the capability that advertises support for in-place
shared memory, and updates the documentation.

Patch 16 adds selftests for the new features.

For details on how to test this patch series, and on how to boot a guest
has uses the new features, please refer to v8 [5].

Cheers,
/fuad

[1] https://lore.kernel.org/all/20250513163438.3942405-1-tabba@google.com/
[2] https://github.com/firecracker-microvm/firecracker/tree/feature/secret-hiding
[3] https://lore.kernel.org/all/20250221160728.1584559-1-roypat@amazon.co.uk/
[4] https://lore.kernel.org/all/20250328153133.3504118-1-tabba@google.com/
[5] https://lore.kernel.org/all/20250430165655.605595-1-tabba@google.com/

Ackerley Tng (2):
  KVM: x86/mmu: Handle guest page faults for guest_memfd with shared
    memory
  KVM: x86: Compute max_mapping_level with input from guest_memfd

Fuad Tabba (14):
  KVM: Rename CONFIG_KVM_PRIVATE_MEM to CONFIG_KVM_GMEM
  KVM: Rename CONFIG_KVM_GENERIC_PRIVATE_MEM to
    CONFIG_KVM_GENERIC_GMEM_POPULATE
  KVM: Rename kvm_arch_has_private_mem() to kvm_arch_supports_gmem()
  KVM: x86: Rename kvm->arch.has_private_mem to kvm->arch.supports_gmem
  KVM: Rename kvm_slot_can_be_private() to kvm_slot_has_gmem()
  KVM: Fix comments that refer to slots_lock
  KVM: Fix comment that refers to kvm uapi header path
  KVM: guest_memfd: Allow host to map guest_memfd pages
  KVM: guest_memfd: Track shared memory support in memslot
  KVM: arm64: Refactor user_mem_abort() calculation of force_pte
  KVM: arm64: Handle guest_memfd-backed guest page faults
  KVM: arm64: Enable mapping guest_memfd in arm64
  KVM: Introduce the KVM capability KVM_CAP_GMEM_SHARED_MEM
  KVM: selftests: guest_memfd mmap() test when mapping is allowed

 Documentation/virt/kvm/api.rst                |   9 +
 arch/arm64/include/asm/kvm_host.h             |   5 +
 arch/arm64/kvm/Kconfig                        |   1 +
 arch/arm64/kvm/mmu.c                          | 109 ++++++++++--
 arch/x86/include/asm/kvm_host.h               |  22 ++-
 arch/x86/kvm/Kconfig                          |   4 +-
 arch/x86/kvm/mmu/mmu.c                        | 135 +++++++++------
 arch/x86/kvm/svm/sev.c                        |   4 +-
 arch/x86/kvm/svm/svm.c                        |   4 +-
 arch/x86/kvm/x86.c                            |   4 +-
 include/linux/kvm_host.h                      |  80 +++++++--
 include/uapi/linux/kvm.h                      |   2 +
 tools/testing/selftests/kvm/Makefile.kvm      |   1 +
 .../testing/selftests/kvm/guest_memfd_test.c  | 162 +++++++++++++++---
 virt/kvm/Kconfig                              |  15 +-
 virt/kvm/Makefile.kvm                         |   2 +-
 virt/kvm/guest_memfd.c                        | 101 ++++++++++-
 virt/kvm/kvm_main.c                           |  16 +-
 virt/kvm/kvm_mm.h                             |   4 +-
 19 files changed, 553 insertions(+), 127 deletions(-)


base-commit: 0ff41df1cb268fc69e703a08a57ee14ae967d0ca
-- 
2.49.0.1164.gab81da1b16-goog