Main changes since v15 [1]:
* 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'").
This patch series enables host userspace mapping of guest_memfd-backed
memory for non-CoCo VMs. This is required for several evolving KVM use
cases:
* Allows VMMs like Firecracker to run guests entirely backed by
guest_memfd [2]. 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 [3], 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 [4] that permit in-place
sharing of guest memory with the host.
Patch breakdown:
* Patches 1-9: Primarily infrastructure refactoring, Kconfig cleaning,
and renames to decouple guest_memfd from the concept of "private"
memory.
* Patches 10-11: Add support for the host to map guest_memfd backed
memory for non-CoCo VMs, which includes support for mmap() and fault
handling. This is gated by a new configuration option, toggled by a
new flag, and advertised to userspace by a new capability (introduced
in patch 20).
* Patches 12-15: Implement x86 guest_memfd mmap support.
* Patches 16-19: Implement arm64 guest_memfd mmap support.
* Patch 20: Introduce the new capability to advertise this support and
update the documentation.
* Patches 21-22: Update and expand selftests for guest_memfd to include
mmap functionality and improve portability.
To test this patch series and boot a guest utilizing the new features,
please refer to the instructions in v8 of the series [5]. Note that
kvmtool for Linux 6.16 (available at [6]) is required, as the
KVM_CAP_GMEM_MMAP capability number has changed, additionally, drop the
--sw_protected kvmtool parameter to test with the default VM type.
Cheers,
/fuad
[1] https://lore.kernel.org/all/20250717162731.446579-1-tabba@xxxxxxxxxx/
[2] https://github.com/firecracker-microvm/firecracker/tree/feature/secret-hiding
[3] https://lore.kernel.org/all/20250221160728.1584559-1-roypat@xxxxxxxxxxxx/
[4] https://lore.kernel.org/all/20250328153133.3504118-1-tabba@xxxxxxxxxx/
[5] https://lore.kernel.org/all/20250430165655.605595-1-tabba@xxxxxxxxxx/
[6] https://android-kvm.googlesource.com/kvmtool/+/refs/heads/tabba/guestmem-basic-6.16
Ackerley Tng (1):
KVM: x86/mmu: Rename .private_max_mapping_level() to
.gmem_max_mapping_level()
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 (6):
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
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 | 143 +++++++-----
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 | 205 +++++++++++++++---
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, 623 insertions(+), 209 deletions(-)
base-commit: 33f843444e28920d6e624c6c24637b4bb5d3c8de
--
2.50.1.470.g6ba607880d-goog
