Main changes since v7 [1]: - Renaming/refactoring to decouple guest memory from whether the underlying memory is private vs being backed by guest_memfd - Drop folio_put() callback patches - Fixes based on feedback from the previous series - Rebase on Linux 6.15-rc4 The purpose of this series is to allow mapping guest_memfd backed memory at the host. This support enables VMMs like Firecracker to run VM guests backed completely by guest_memfd [2]. Combined with Patrick's series for direct map removal in guest_memfd [3], this would allow running VMs that offer additional hardening against Spectre-like transient execution attacks. This series will also serve as a base for _restricted_ mmap() support for guest_memfd backed memory at the host for CoCos that allow sharing guest memory in-place with the host [4]. Patches 1 to 7 are mainly about decoupling the concept of guest memory being private vs guest memory being backed by guest_memfd. They are mostly refactoring and renaming. Patch 8 adds support for in-place shared memory, as well as the ability to map it by the host as long as it is shared, gated by a new configuration option, and adviertised to userspace by a new capability. Patches 9 to 12 add arm64 and x86 support for in-place shared memory. Patch 13 expands the guest_memfd selftest to test in-place shared memory when avaialble. 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 Additional config options to enable: 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 [5] 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 [5] 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 [6]. Cheers, /fuad [1] https://lore.kernel.org/all/20250318161823.4005529-1-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://android-kvm.googlesource.com/kvmtool/+/refs/heads/tabba/guestmem-basic-6.15 [6] https://mirrors.edge.kernel.org/pub/linux/kernel/people/will/docs/qemu/qemu-arm64-howto.html Fuad Tabba (13): KVM: Rename CONFIG_KVM_PRIVATE_MEM to CONFIG_KVM_GMEM KVM: Rename CONFIG_KVM_GENERIC_PRIVATE_MEM to CONFIG_KVM_GENERIC_GMEM_POPULATE KVM: Rename kvm_arch_has_private_mem() to kvm_arch_supports_gmem() KVM: x86: Rename kvm->arch.has_private_mem to kvm->arch.supports_gmem KVM: Rename kvm_slot_can_be_private() to kvm_slot_has_gmem() KVM: x86: Generalize private fault lookups to guest_memfd fault lookups KVM: Fix comments that refer to slots_lock KVM: guest_memfd: Allow host to map guest_memfd() pages KVM: arm64: Refactor user_mem_abort() calculation of force_pte KVM: arm64: Handle guest_memfd()-backed guest page faults KVM: arm64: Enable mapping guest_memfd in arm64 KVM: x86: KVM_X86_SW_PROTECTED_VM to support guest_memfd shared memory KVM: guest_memfd: selftests: guest_memfd mmap() test when mapping is allowed arch/arm64/include/asm/kvm_host.h | 12 +++ arch/arm64/kvm/Kconfig | 1 + arch/arm64/kvm/mmu.c | 76 +++++++++------ arch/x86/include/asm/kvm_host.h | 17 ++-- arch/x86/kvm/Kconfig | 4 +- arch/x86/kvm/mmu/mmu.c | 31 +++--- arch/x86/kvm/svm/sev.c | 4 +- arch/x86/kvm/svm/svm.c | 4 +- arch/x86/kvm/x86.c | 3 +- include/linux/kvm_host.h | 44 +++++++-- include/uapi/linux/kvm.h | 1 + tools/testing/selftests/kvm/Makefile.kvm | 1 + .../testing/selftests/kvm/guest_memfd_test.c | 75 +++++++++++++-- virt/kvm/Kconfig | 15 ++- virt/kvm/Makefile.kvm | 2 +- virt/kvm/guest_memfd.c | 96 ++++++++++++++++++- virt/kvm/kvm_main.c | 21 ++-- virt/kvm/kvm_mm.h | 4 +- 18 files changed, 316 insertions(+), 95 deletions(-) base-commit: b4432656b36e5cc1d50a1f2dc15357543add530e -- 2.49.0.901.g37484f566f-goog
