[PATCH v17 00/24] KVM: Enable mmap() for guest_memfd

[Sean Christopherson <seanjc@google.com>]

Paolo,

The arm64 patches have been Reviewed-by Marc, and AFAICT the x86 side of
things is a go.  Barring a screwup on my end, this just needs your approval.

Assuming everything looks good, it'd be helpful to get this into kvm/next
shortly after rc1.  The x86 Kconfig changes in particular create semantic
conflicts with in-flight series.


Add support for host userspace mapping of guest_memfd-backed memory for VM
types that do NOT use support KVM_MEMORY_ATTRIBUTE_PRIVATE (which isn't
precisely the same thing as CoCo VMs, since x86's SEV-MEM and SEV-ES have
no way to detect private vs. shared).

mmap() support paves the way for several evolving KVM use cases:

 * Allows VMMs like Firecracker to run guests entirely backed by
   guest_memfd [1]. This provides a unified memory management model for
   both confidential and non-confidential guests, simplifying VMM design.

 * Enhanced Security via direct map removal: When combined with Patrick's
   series for direct map removal [2], this provides additional hardening
   against Spectre-like transient execution attacks by eliminating the
   need for host kernel direct maps of guest memory.

 * Lays the groundwork for *restricted* mmap() support for guest_memfd-backed
   memory on CoCo platforms [3] that permit in-place
   sharing of guest memory with the host.

Based on kvm/queue.

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

v17:
 - Collect reviews. [Xiaoyao, David H.]
 - Write a better changelog for the CONFIG_KVM_GENERIC_PRIVATE_MEM =>
   CONFIG_HAVE_KVM_ARCH_GMEM_POPULATE rename. [Xiaoyao]
 - Correctly gmem_max_mapping_level()'s '0' return in the right patch. [Xiaoyao]
 - Replace call to kvm_gmem_get_pfn() with a WARN_ONCE() in the hugepage
   recovery path. [Ackerley]
 - Add back "KVM: x86/mmu: Handle guest page faults for guest_memfd with
   shared memory". [Ackerley]
 - Rework the selftest flags testcase to query MMAP support for a given VM
   type instead of hardcoding expectations in the test. [Sean]
 - Add a testcase to verify KVM can map guest_memfd memory into the guest
   even if the userspace address in the memslot isn't (properly) mmap'd. [Sean]

v16:
 - https://lore.kernel.org/all/20250723104714.1674617-1-tabba@google.com
 - Rework and simplify Kconfig selection and dependencies.
 - Always enable guest_memfd for KVM x86 (64-bit) and arm64, which
   simplifies the enablement checks.
 - Based on kvm-x86/next: commit 33f843444e28 ("Merge branch 'vmx'").

v15:
 - https://lore.kernel.org/all/20250717162731.446579-1-tabba@google.com
 - Removed KVM_SW_PROTECTED_VM dependency on KVM_GENERIC_GMEM_POPULATE
 - Fixed some commit messages

v14:
 - https://lore.kernel.org/all/20250715093350.2584932-1-tabba@google.com
 - Fixed handling of guest faults in case of invalidation in arm64
 - Handle VNCR_EL2-triggered faults backed by guest_memfd (arm64 nested
   virt)
 - Applied suggestions from latest feedback
 - Rebase on Linux 6.16-rc6

Ackerley Tng (2):
  KVM: x86/mmu: Rename .private_max_mapping_level() to
    .gmem_max_mapping_level()
  KVM: x86/mmu: Handle guest page faults for guest_memfd with shared
    memory

Fuad Tabba (15):
  KVM: Rename CONFIG_KVM_PRIVATE_MEM to CONFIG_KVM_GUEST_MEMFD
  KVM: Rename CONFIG_KVM_GENERIC_PRIVATE_MEM to
    CONFIG_HAVE_KVM_ARCH_GMEM_POPULATE
  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: x86: Enable KVM_GUEST_MEMFD for all 64-bit builds
  KVM: guest_memfd: Add plumbing to host to map guest_memfd pages
  KVM: guest_memfd: Track guest_memfd mmap support in memslot
  KVM: arm64: Refactor user_mem_abort()
  KVM: arm64: Handle guest_memfd-backed guest page faults
  KVM: arm64: nv: Handle VNCR_EL2-triggered faults backed by guest_memfd
  KVM: arm64: Enable support for guest_memfd backed memory
  KVM: Allow and advertise support for host mmap() on guest_memfd files
  KVM: selftests: Do not use hardcoded page sizes in guest_memfd test
  KVM: selftests: guest_memfd mmap() test when mmap is supported

Sean Christopherson (7):
  KVM: x86: Have all vendor neutral sub-configs depend on KVM_X86, not
    just KVM
  KVM: x86: Select KVM_GENERIC_PRIVATE_MEM directly from
    KVM_SW_PROTECTED_VM
  KVM: x86: Select TDX's KVM_GENERIC_xxx dependencies iff
    CONFIG_KVM_INTEL_TDX=y
  KVM: x86/mmu: Hoist guest_memfd max level/order helpers "up" in mmu.c
  KVM: x86/mmu: Enforce guest_memfd's max order when recovering
    hugepages
  KVM: x86/mmu: Extend guest_memfd's max mapping level to shared
    mappings
  KVM: selftests: Add guest_memfd testcase to fault-in on !mmap()'d
    memory

 Documentation/virt/kvm/api.rst                |   9 +
 arch/arm64/kvm/Kconfig                        |   1 +
 arch/arm64/kvm/mmu.c                          | 203 +++++++++++----
 arch/arm64/kvm/nested.c                       |  41 ++-
 arch/x86/include/asm/kvm-x86-ops.h            |   2 +-
 arch/x86/include/asm/kvm_host.h               |   6 +-
 arch/x86/kvm/Kconfig                          |  26 +-
 arch/x86/kvm/mmu/mmu.c                        | 142 ++++++-----
 arch/x86/kvm/mmu/mmu_internal.h               |   2 +-
 arch/x86/kvm/mmu/tdp_mmu.c                    |   2 +-
 arch/x86/kvm/svm/sev.c                        |   6 +-
 arch/x86/kvm/svm/svm.c                        |   2 +-
 arch/x86/kvm/svm/svm.h                        |   4 +-
 arch/x86/kvm/vmx/main.c                       |   7 +-
 arch/x86/kvm/vmx/tdx.c                        |   5 +-
 arch/x86/kvm/vmx/x86_ops.h                    |   2 +-
 arch/x86/kvm/x86.c                            |  11 +
 include/linux/kvm_host.h                      |  38 +--
 include/uapi/linux/kvm.h                      |   2 +
 tools/testing/selftests/kvm/Makefile.kvm      |   1 +
 .../testing/selftests/kvm/guest_memfd_test.c  | 236 ++++++++++++++++--
 virt/kvm/Kconfig                              |  15 +-
 virt/kvm/Makefile.kvm                         |   2 +-
 virt/kvm/guest_memfd.c                        |  81 +++++-
 virt/kvm/kvm_main.c                           |  12 +-
 virt/kvm/kvm_mm.h                             |   4 +-
 26 files changed, 648 insertions(+), 214 deletions(-)


base-commit: beafd7ecf2255e8b62a42dc04f54843033db3d24
-- 
2.50.1.552.g942d659e1b-goog