Main changes since v13 [1]: * 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 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 1-7: Primarily infrastructure refactorings and renames to decouple guest_memfd from the concept of "private" memory. Patches 8-9: 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 18). Patches 10-14: Implement x86 guest_memfd mmap support. Patches 15-18: Implement arm64 guest_memfd mmap support. Patch 19: Introduce the new capability to advertise this support and update the documentation. Patches 20-21: 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/20250709105946.4009897-1-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 (4): KVM: x86/mmu: Generalize private_max_mapping_level x86 op to max_mapping_level KVM: x86/mmu: Allow NULL-able fault in kvm_max_private_mapping_level KVM: x86/mmu: Consult guest_memfd when computing max_mapping_level KVM: x86/mmu: Handle guest page faults for guest_memfd with shared memory Fuad Tabba (17): KVM: Rename CONFIG_KVM_PRIVATE_MEM to CONFIG_KVM_GMEM KVM: Rename CONFIG_KVM_GENERIC_PRIVATE_MEM to CONFIG_KVM_GENERIC_GMEM_POPULATE KVM: Introduce kvm_arch_supports_gmem() KVM: x86: Introduce 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 guest_memfd mmap support in memslot KVM: x86: Enable guest_memfd mmap for default VM type 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 host mapping of shared guest_memfd memory KVM: Introduce the KVM capability KVM_CAP_GMEM_MMAP KVM: selftests: Do not use hardcoded page sizes in guest_memfd test KVM: selftests: guest_memfd mmap() test when mmap is supported Documentation/virt/kvm/api.rst | 9 + arch/arm64/include/asm/kvm_host.h | 4 + arch/arm64/kvm/Kconfig | 2 + 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 | 18 +- arch/x86/kvm/Kconfig | 7 +- arch/x86/kvm/mmu/mmu.c | 114 ++++++---- arch/x86/kvm/svm/sev.c | 12 +- arch/x86/kvm/svm/svm.c | 3 +- arch/x86/kvm/svm/svm.h | 4 +- arch/x86/kvm/vmx/main.c | 6 +- arch/x86/kvm/vmx/tdx.c | 6 +- arch/x86/kvm/vmx/x86_ops.h | 2 +- arch/x86/kvm/x86.c | 5 +- include/linux/kvm_host.h | 64 +++++- include/uapi/linux/kvm.h | 2 + tools/testing/selftests/kvm/Makefile.kvm | 1 + .../testing/selftests/kvm/guest_memfd_test.c | 208 +++++++++++++++--- virt/kvm/Kconfig | 14 +- virt/kvm/Makefile.kvm | 2 +- virt/kvm/guest_memfd.c | 96 +++++++- virt/kvm/kvm_main.c | 14 +- virt/kvm/kvm_mm.h | 4 +- 25 files changed, 664 insertions(+), 179 deletions(-) base-commit: 347e9f5043c89695b01e66b3ed111755afcf1911 -- 2.50.0.727.gbf7dc18ff4-goog
