mbox series

[v12,00/18] KVM: Mapping guest_memfd backed memory at the host for software protected VMs

Message ID 20250611133330.1514028-1-tabba@google.com
Headers show
Series KVM: Mapping guest_memfd backed memory at the host for software protected VMs | expand

Message

Fuad Tabba June 11, 2025, 1:33 p.m. UTC 
Main changes since v11 [1]:
- Addressed various points of feedback from the last revision.
- Rebased on Linux 6.16-rc1.

This patch series enables mapping of guest_memfd backed memory in the
host. This is useful for VMMs like Firecracker that aim to run guests
entirely backed by guest_memfd [2]. When combined with Patrick's series
for direct map removal [3], this provides additional hardening against
Spectre-like transient execution attacks.

This series also lays the groundwork for restricted mmap() support for
guest_memfd backed memory in the host for Confidential Computing
platforms that permit in-place sharing of guest memory with the host
[4].

Patch breakdown:

Patches 1-7: Primarily refactoring and renaming to decouple the concept
of guest memory being "private" from it being backed by guest_memfd.

Patches 8-9: Add support for in-place shared memory and the ability for
the host to map it. This is gated by a new configuration option, toggled
by a new flag, and advertised to userspace by a new capability
(introduced in patch 16).

Patches 10-15: Implement the x86 and arm64 support for this feature.

Patch 16: Introduces the new capability to advertise this support and
updates the documentation.

Patches 17-18: Add and fix selftests for the new functionality.

For details on how to test this patch series, and on how to boot a guest
that uses the new features, please refer to the instructions in v8 [5],
but use the updated kvmtool for 6.16 (KVM_CAP_GMEM_SHARED_MEM number has
changed) [6].

Cheers,
/fuad

[1] https://lore.kernel.org/all/20250605153800.557144-1-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/
[6] https://android-kvm.googlesource.com/kvmtool/+/refs/heads/tabba/guestmem-basic-6.16

Ackerley Tng (2):
  KVM: x86/mmu: Handle guest page faults for guest_memfd with shared
    memory
  KVM: x86: Consult guest_memfd when computing max_mapping_level

Fuad Tabba (16):
  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: x86: Enable guest_memfd shared memory for non-CoCo VMs
  KVM: arm64: Refactor user_mem_abort()
  KVM: arm64: Handle guest_memfd-backed guest page faults
  KVM: arm64: Enable host mapping of shared guest_memfd memory
  KVM: Introduce the KVM capability KVM_CAP_GMEM_SHARED_MEM
  KVM: selftests: Don't use hardcoded page sizes in guest_memfd test
  KVM: selftests: guest_memfd mmap() test when mapping is allowed

 Documentation/virt/kvm/api.rst                |   9 +
 arch/arm64/include/asm/kvm_host.h             |   4 +
 arch/arm64/kvm/Kconfig                        |   1 +
 arch/arm64/kvm/mmu.c                          | 189 ++++++++++++----
 arch/x86/include/asm/kvm_host.h               |  22 +-
 arch/x86/kvm/Kconfig                          |   5 +-
 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  | 212 +++++++++++++++---
 virt/kvm/Kconfig                              |  14 +-
 virt/kvm/Makefile.kvm                         |   2 +-
 virt/kvm/guest_memfd.c                        |  91 +++++++-
 virt/kvm/kvm_main.c                           |  16 +-
 virt/kvm/kvm_mm.h                             |   4 +-
 19 files changed, 630 insertions(+), 169 deletions(-)


base-commit: 19272b37aa4f83ca52bdf9c16d5d81bdd1354494