Main changes since v1 [1]: - Added x86 support for mapping guest_memfd at the host, enabled only for the KVM_X86_SW_PROTECTED_VM type. - Require setting memslot userspace_addr for guest_memfd slots even if shared, and remove patches that worked around that. - Brought in more of the infrastructure from the patch series that allows restricted mapping of guest_memfd backed memory. - Renamed references to "mappable" -> "shared". - Expanded the selftests. - Added instructions to test on x86 and arm64 (below). - Rebased on Linux 6.13. The purpose of this series is to serve as a base for _restricted_ mmap() support for guest_memfd backed memory at the host [2]. It would allow experimentation with what that support would be like in the safe environment of the software VM types, which are meant for testing and experimentation. This series adds a new VM type for arm64, KVM_VM_TYPE_ARM_SW_PROTECTED, analogous to the x86 KVM_X86_SW_PROTECTED_VM. This type is to serve as a development and testing vehicle for Confidential (CoCo) VMs. Similar to its x86 counterpart, SW_PROTECTED is meant only for development and testing. It's not meant to be used for "real" VMs, and especially not in production. The behavior and effective ABI for software-protected VMs is unstable. This series enables mmap() and fault() support for guest_memfd backed memory specifically for the software-protected VM types (in x86 and arm64), only when explicitly enabled in the config. The series is based on Linux 6.13 and much of the code within is a subset of the latest series I sent [2], with the addition of the new software protected vm type. To test this series, I've pushed a kvmtool branch with support for guest_memfd for x86 and arm64 and the new runtime options of --guest_memfd and --sw_protected, which marks the VM as software protected [3]. I plan on upstreaming this branch once I've tested it more and tidied it up a bit (or a lot). To test this patch series on x86 (I use a standard Debian image): Build: - Build the kernel with the following config options enabled: defconfigs: x86_64_defconfig kvm_guest.config config options: KVM KVM_INTEL KVM_PRIVATE_MEM KVM_SW_PROTECTED_VM KVM_GMEM_SHARED_MEM - Build the kernel kvm selftest tools/testing/selftests/kvm, you only need guest_memfd_test, e.g.: make EXTRA_CFLAGS="-static -DDEBUG" -C tools/testing/selftests/kvm - Build kvmtool [3] lkvm-static (I build it on a different machine). make lkvm-static Run: Boot your Linux image with the kernel you built above. The selftest you can run as it is: ./guest_memfd_test For kvmtool, where bzImage is the same as the host's: ./lkvm-static run -c 2 -m 512 -p "break=mount" --kernel bzImage --debug --guest_memfd --sw_protected To test this patch series on arm64 (I use a standard Debian image): Build: - Build the kernel with defconfig - Build the kernel kvm selftest tools/testing/selftests/kvm, you only need guest_memfd_test. - Build kvmtool [3] lkvm-static (I cross compile it on a different machine). You are likely to need libfdt as well. For libfdt (in the same directory as kvmtool): git clone git://git.kernel.org/pub/scm/utils/dtc/dtc.git cd dtc export CC=aarch64-linux-gnu-gcc make cd .. Then for kvmtool: make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- LIBFDT_DIR=./dtc/libfdt/ lkvm-static Run: Boot your Linux image with the kernel you built above. The selftest you can run as it is: ./guest_memfd_test For kvmtool, where Image is the same as the host's, and rootfs is your rootfs image (in case kvmtool can't figure it out): ./lkvm-static run -c 2 -m 512 -d rootfs --kernel Image --force-pci --irqchip gicv3 --debug --guest_memfd --sw_protected You can find (potentially slightly outdated) instructions on how to a full arm64 system stack under QEMU here [4]. Cheers, /fuad [1] https://lore.kernel.org/all/20250122152738.1173160-1-tabba@xxxxxxxxxx/ [2] https://lore.kernel.org/all/20250117163001.2326672-1-tabba@xxxxxxxxxx/ [3] https://android-kvm.googlesource.com/kvmtool/+/refs/heads/tabba/guestmem-6.13 [4] https://mirrors.edge.kernel.org/pub/linux/kernel/people/will/docs/qemu/qemu-arm64-howto.html Fuad Tabba (11): mm: Consolidate freeing of typed folios on final folio_put() KVM: guest_memfd: Handle final folio_put() of guest_memfd pages KVM: guest_memfd: Allow host to map guest_memfd() pages KVM: guest_memfd: Add KVM capability to check if guest_memfd is shared KVM: guest_memfd: Handle in-place shared memory as guest_memfd backed memory KVM: x86: Mark KVM_X86_SW_PROTECTED_VM as supporting guest_memfd shared memory KVM: arm64: Refactor user_mem_abort() calculation of force_pte KVM: arm64: Handle guest_memfd()-backed guest page faults KVM: arm64: Introduce KVM_VM_TYPE_ARM_SW_PROTECTED machine type KVM: arm64: Enable mapping guest_memfd in arm64 KVM: guest_memfd: selftests: guest_memfd mmap() test when mapping is allowed Documentation/virt/kvm/api.rst | 5 + arch/arm64/include/asm/kvm_host.h | 10 ++ arch/arm64/kvm/Kconfig | 1 + arch/arm64/kvm/arm.c | 5 + arch/arm64/kvm/mmu.c | 91 ++++++++++++------- arch/x86/include/asm/kvm_host.h | 5 + arch/x86/kvm/Kconfig | 3 +- include/linux/kvm_host.h | 19 +++- include/linux/page-flags.h | 22 +++++ include/uapi/linux/kvm.h | 7 ++ mm/debug.c | 1 + mm/swap.c | 27 +++++- tools/testing/selftests/kvm/Makefile | 1 + .../testing/selftests/kvm/guest_memfd_test.c | 75 +++++++++++++-- tools/testing/selftests/kvm/lib/kvm_util.c | 3 +- virt/kvm/Kconfig | 4 + virt/kvm/guest_memfd.c | 90 ++++++++++++++++++ virt/kvm/kvm_main.c | 9 +- 18 files changed, 326 insertions(+), 52 deletions(-) base-commit: ffd294d346d185b70e28b1a28abe367bbfe53c04 -- 2.48.1.262.g85cc9f2d1e-goog
