mbox series

[v9,00/17] KVM: Mapping guest_memfd backed memory at the host for software protected VMs

Message ID 20250513163438.3942405-1-tabba@google.com
Headers show
Series KVM: Mapping guest_memfd backed memory at the host for software protected VMs | expand

Message

Fuad Tabba May 13, 2025, 4:34 p.m. UTC 
Main changes since v8 [1]:
- Added guest_memfd flag that toggles support for in-place shared memory
- Added 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 x86
- Fixes based on feedback from the previous series
- Rebase on Linux 6.15-rc6

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 6 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 7 and 8 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 9 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.

Patches 16 and 17 add new selftests for the added 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 [1].

Cheers,
/fuad

[1] https://lore.kernel.org/all/20250430165655.605595-1-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/

Ackerley Tng (4):
  KVM: guest_memfd: Check that userspace_addr and fd+offset refer to
    same range
  KVM: x86/mmu: Handle guest page faults for guest_memfd with shared
    memory
  KVM: x86: Compute max_mapping_level with input from guest_memfd
  KVM: selftests: Test guest_memfd same-range validation

Fuad Tabba (13):
  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: guest_memfd: Allow host to map guest_memfd() pages
  KVM: arm64: Refactor user_mem_abort() calculation of force_pte
  KVM: arm64: Rename variables in user_mem_abort()
  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                |  18 +
 arch/arm64/include/asm/kvm_host.h             |  10 +
 arch/arm64/kvm/Kconfig                        |   1 +
 arch/arm64/kvm/mmu.c                          | 149 +++++----
 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                            |   3 +-
 include/linux/kvm_host.h                      |  76 ++++-
 include/uapi/linux/kvm.h                      |   2 +
 tools/testing/selftests/kvm/Makefile.kvm      |   1 +
 .../testing/selftests/kvm/guest_memfd_test.c  | 313 ++++++++++++++++--
 virt/kvm/Kconfig                              |  15 +-
 virt/kvm/Makefile.kvm                         |   2 +-
 virt/kvm/guest_memfd.c                        | 152 ++++++++-
 virt/kvm/kvm_main.c                           |  21 +-
 virt/kvm/kvm_mm.h                             |   4 +-
 19 files changed, 753 insertions(+), 183 deletions(-)


base-commit: 82f2b0b97b36ee3fcddf0f0780a9a0825d52fec3