[PATCH v8 00/13] Direct Map Removal Support for guest_memfd

["Kalyazin, Nikita" <kalyazin@amazon.co.uk>]

[ based on kvm/next ]

Unmapping virtual machine guest memory from the host kernel's direct map
is a successful mitigation against Spectre-style transient execution
issues: if the kernel page tables do not contain entries pointing to
guest memory, then any attempted speculative read through the direct map
will necessarily be blocked by the MMU before any observable
microarchitectural side-effects happen.  This means that Spectre-gadgets
and similar cannot be used to target virtual machine memory.  Roughly
60% of speculative execution issues fall into this category [1, Table
1].

This patch series extends guest_memfd with the ability to remove its
memory from the host kernel's direct map, to be able to attain the above
protection for KVM guests running inside guest_memfd.

Additionally, a Firecracker branch with support for these VMs can be
found on GitHub [2].

For more details, please refer to the v5 cover letter.  No substantial
changes in design have taken place since.

See also related write() syscall support in guest_memfd [3] where
the interoperation between the two features is described.

Changes since v7:
 - David: separate patches for adding x86 and ARM support
 - Dave/Will: drop support for disabling TLB flushes

v7: https://lore.kernel.org/kvm/20250924151101.2225820-1-patrick.roy@campus.lmu.de
v6: https://lore.kernel.org/kvm/20250912091708.17502-1-roypat@amazon.co.uk
v5: https://lore.kernel.org/kvm/20250828093902.2719-1-roypat@amazon.co.uk
v4: https://lore.kernel.org/kvm/20250221160728.1584559-1-roypat@amazon.co.uk
RFCv3: https://lore.kernel.org/kvm/20241030134912.515725-1-roypat@amazon.co.uk
RFCv2: https://lore.kernel.org/kvm/20240910163038.1298452-1-roypat@amazon.co.uk
RFCv1: https://lore.kernel.org/kvm/20240709132041.3625501-1-roypat@amazon.co.uk

[1] https://download.vusec.net/papers/quarantine_raid23.pdf
[2] https://github.com/firecracker-microvm/firecracker/tree/feature/secret-hiding
[3] https://lore.kernel.org/kvm/20251114151828.98165-1-kalyazin@amazon.com

Patrick Roy (13):
  x86: export set_direct_map_valid_noflush to KVM module
  x86/tlb: export flush_tlb_kernel_range to KVM module
  mm: introduce AS_NO_DIRECT_MAP
  KVM: guest_memfd: Add stub for kvm_arch_gmem_invalidate
  KVM: guest_memfd: Add flag to remove from direct map
  KVM: x86: define kvm_arch_gmem_supports_no_direct_map()
  KVM: arm64: define kvm_arch_gmem_supports_no_direct_map()
  KVM: selftests: load elf via bounce buffer
  KVM: selftests: set KVM_MEM_GUEST_MEMFD in vm_mem_add() if guest_memfd
    != -1
  KVM: selftests: Add guest_memfd based vm_mem_backing_src_types
  KVM: selftests: cover GUEST_MEMFD_FLAG_NO_DIRECT_MAP in existing
    selftests
  KVM: selftests: stuff vm_mem_backing_src_type into vm_shape
  KVM: selftests: Test guest execution from direct map removed gmem

 Documentation/virt/kvm/api.rst                | 22 ++++---
 arch/arm64/include/asm/kvm_host.h             | 13 ++++
 arch/x86/include/asm/kvm_host.h               |  9 +++
 arch/x86/include/asm/tlbflush.h               |  3 +-
 arch/x86/mm/pat/set_memory.c                  |  1 +
 arch/x86/mm/tlb.c                             |  1 +
 include/linux/kvm_host.h                      | 14 ++++
 include/linux/pagemap.h                       | 16 +++++
 include/linux/secretmem.h                     | 18 ------
 include/uapi/linux/kvm.h                      |  1 +
 lib/buildid.c                                 |  4 +-
 mm/gup.c                                      | 19 ++----
 mm/mlock.c                                    |  2 +-
 mm/secretmem.c                                |  8 +--
 .../testing/selftests/kvm/guest_memfd_test.c  | 17 ++++-
 .../testing/selftests/kvm/include/kvm_util.h  | 37 ++++++++---
 .../testing/selftests/kvm/include/test_util.h |  8 +++
 tools/testing/selftests/kvm/lib/elf.c         |  8 +--
 tools/testing/selftests/kvm/lib/io.c          | 23 +++++++
 tools/testing/selftests/kvm/lib/kvm_util.c    | 59 +++++++++--------
 tools/testing/selftests/kvm/lib/test_util.c   |  8 +++
 tools/testing/selftests/kvm/lib/x86/sev.c     |  1 +
 .../selftests/kvm/pre_fault_memory_test.c     |  1 +
 .../selftests/kvm/set_memory_region_test.c    | 52 +++++++++++++--
 .../kvm/x86/private_mem_conversions_test.c    |  7 +-
 virt/kvm/guest_memfd.c                        | 64 +++++++++++++++++--
 26 files changed, 314 insertions(+), 102 deletions(-)


base-commit: e0c26d47def7382d7dbd9cad58bc653aed75737a
-- 
2.50.1