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It would be nice to hear about your opinions on that. UML has been built with CONFIG_MMU since day 0. The patchset introduces the nommu mode on UML in a different angle in order to cover broader code to be executed over UML. More details are in the document which are included in this patchset. There are still several limitations/issues which we already found; here is the list of those issues. - memory mapped by loadable modules are not distinguished from userspace memory. - CONFIG_SMP is disabled as host_fs handling doesn't work with thread local storage. -- Hajime v14: - rebase with the latest uml/next branch - clean up fs register manipulation code ([07/13]) - fix compilation issue when time-travel mode is enabled ([02/13]) - refresh document to clarify the goals ([12/13]) v13: - rebase with the latest uml/next branch, fixing a conflict ([06/13]) - https://lore.kernel.org/all/cover.1762588860.git.thehajime@gmail.com/ v12: - rebase with the latest uml/next branch - disable SMP and tls as those doesn't work with host_fs handling ([11/13]) - https://lore.kernel.org/all/cover.1762075876.git.thehajime@gmail.com/ v11: - clean up userspace return routine and integrate to userspace() ([04/13]) - fix direction flag issue on using nolibc memcpy ([04/13]) - fix a crash issue when using usermode helper ([06/13]) - test with out-of-tree kunit-uapi patches (which uses umh) - https://lore.kernel.org/all/20250626-kunit-kselftests-v4-0-48760534fef5@linutronix.de/ - https://lore.kernel.org/all/20250626195714.2123694-3-benjamin@sipsolutions.net/ - https://lore.kernel.org/all/cover.1758181109.git.thehajime@gmail.com/ v10: - fix wrong comment on gs register handling ([09/13]) - remove unnecessary code of early syscall implementation ([04/13]) - https://lore.kernel.org/all/cover.1750594487.git.thehajime@gmail.com/ v9: - rebase with the latest uml/next branch - add performance numbers of new SECCOMP mode, and update results ([12/13]) - add a workaround for upstream change on MMU depedency to PCI drivers ([10/13]) - https://lore.kernel.org/all/cover.1750294482.git.thehajime@gmail.com/ v8: - rebase with the latest uml/next branch - clean up segv_handler to align with the latest uml ([9/12]) - https://lore.kernel.org/all/cover.1745980082.git.thehajime@gmail.com/ v7: - properly handle FP register upon signal delivery [10/13] - update benchmark result with new FP register handling [12/13] - fix arch_has_single_step() for !MMU case [07/13] - revert stack alignment as it is in uml/fixes tree [10/13] - https://lore.kernel.org/all/cover.1737348399.git.thehajime@gmail.com/ v6: - rebase to the latest uml/next tree - more clean up on mmu/nommu for signal handling [10/13] - rename functions of mcontext routines [06,10/13] - added Acked-by tag for binfmt_elf_fdpic [02/13] - https://lore.kernel.org/linux-um/cover.1736853925.git.thehajime@gmail.com/ v5: - clean up stack manipulation code [05,06,07,10/13] - https://lore.kernel.org/linux-um/cover.1733998168.git.thehajime@gmail.com/ v4: - add arch/um/nommu, arch/x86/um/nommu to contain !MMU specific codes - remove zpoline patch - drop binfmt_elf_fdpic patch - reduce ifndef CONFIG_MMU if possible - split to elf header cleanup patch [01/13] - fix kernel test robot warnings [06/13] - fix coding styles [07/13] - move task_top_of_stack definition [05/13] - https://lore.kernel.org/linux-um/cover.1733652929.git.thehajime@gmail.com/ v3: - https://lore.kernel.org/linux-um/cover.1733199769.git.thehajime@gmail.com/ - add seccomp-based syscall hook in addition to zpoline [06/13] - remove RFC, add a line to MAINTAINERS file - fix kernel test robot warnings [02/13,08/13,10/13] - add base-commit tag to cover letter - pull the latest uml/next - clean up SIGSEGV handling [10/13] - detect fsgsbase availability with elf aux vector [08/13] - simplify vdso code with macros [09/13] RFC v2: - https://lore.kernel.org/linux-um/cover.1731290567.git.thehajime@gmail.com/ - base branch is now uml/linux.git instead of torvalds/linux.git. - reorganize the patch series to clean up - fixed various coding styles issues - clean up exec code path [07/13] - fixed the crash/SIGSEGV case on userspace programs [10/13] - add seccomp filter to limit syscall caller address [06/13] - detect fsgsbase availability with sigsetjmp/siglongjmp [08/13] - removes unrelated changes - removes unneeded ifndef CONFIG_MMU - convert UML_CONFIG_MMU to CONFIG_MMU as using uml/linux.git - proposed a patch of maple-tree issue (resolving a limitation in RFC v1) https://lore.kernel.org/linux-mm/20241108222834.3625217-1-thehajime@gmail.com/ RFC: - https://lore.kernel.org/linux-um/cover.1729770373.git.thehajime@gmail.com/ Hajime Tazaki (13): x86/um: nommu: elf loader for fdpic um: decouple MMU specific code from the common part um: nommu: memory handling x86/um: nommu: syscall handling um: nommu: seccomp syscalls hook x86/um: nommu: process/thread handling um: nommu: configure fs register on host syscall invocation x86/um/vdso: nommu: vdso memory update x86/um: nommu: signal handling um: change machine name for uname output um: nommu: disable SMP on nommu UML um: nommu: add documentation of nommu UML um: nommu: plug nommu code into build system Documentation/virt/uml/nommu-uml.rst | 181 ++++++++++++++++++++++ MAINTAINERS | 1 + arch/um/Kconfig | 14 +- arch/um/Makefile | 10 ++ arch/um/configs/x86_64_nommu_defconfig | 54 +++++++ arch/um/include/asm/futex.h | 4 + arch/um/include/asm/mmu.h | 8 + arch/um/include/asm/mmu_context.h | 2 + arch/um/include/asm/ptrace-generic.h | 8 +- arch/um/include/asm/uaccess.h | 7 +- arch/um/include/shared/kern_util.h | 6 + arch/um/include/shared/os.h | 16 ++ arch/um/kernel/Makefile | 5 +- arch/um/kernel/mem-pgtable.c | 55 +++++++ arch/um/kernel/mem.c | 38 +---- arch/um/kernel/process.c | 38 +++++ arch/um/kernel/skas/process.c | 37 ----- arch/um/kernel/um_arch.c | 3 + arch/um/nommu/Makefile | 3 + arch/um/nommu/os-Linux/Makefile | 7 + arch/um/nommu/os-Linux/seccomp.c | 87 +++++++++++ arch/um/nommu/os-Linux/signal.c | 24 +++ arch/um/nommu/trap.c | 201 +++++++++++++++++++++++++ arch/um/os-Linux/Makefile | 3 +- arch/um/os-Linux/internal.h | 8 + arch/um/os-Linux/mem.c | 4 + arch/um/os-Linux/process.c | 139 ++++++++++++++++- arch/um/os-Linux/signal.c | 11 +- arch/um/os-Linux/skas/process.c | 128 +--------------- arch/um/os-Linux/start_up.c | 25 ++- arch/um/os-Linux/util.c | 3 +- arch/x86/um/Kconfig | 2 +- arch/x86/um/Makefile | 4 + arch/x86/um/asm/elf.h | 8 +- arch/x86/um/asm/syscall.h | 6 + arch/x86/um/nommu/Makefile | 8 + arch/x86/um/nommu/do_syscall_64.c | 49 ++++++ arch/x86/um/nommu/entry_64.S | 114 ++++++++++++++ arch/x86/um/nommu/os-Linux/Makefile | 6 + arch/x86/um/nommu/os-Linux/mcontext.c | 26 ++++ arch/x86/um/nommu/syscalls.h | 19 +++ arch/x86/um/nommu/syscalls_64.c | 86 +++++++++++ arch/x86/um/shared/sysdep/mcontext.h | 5 + arch/x86/um/shared/sysdep/ptrace.h | 2 +- arch/x86/um/syscalls_64.c | 2 +- arch/x86/um/vdso/vma.c | 17 ++- fs/Kconfig.binfmt | 2 +- 47 files changed, 1263 insertions(+), 223 deletions(-) create mode 100644 Documentation/virt/uml/nommu-uml.rst create mode 100644 arch/um/configs/x86_64_nommu_defconfig create mode 100644 arch/um/kernel/mem-pgtable.c create mode 100644 arch/um/nommu/Makefile create mode 100644 arch/um/nommu/os-Linux/Makefile create mode 100644 arch/um/nommu/os-Linux/seccomp.c create mode 100644 arch/um/nommu/os-Linux/signal.c create mode 100644 arch/um/nommu/trap.c create mode 100644 arch/x86/um/nommu/Makefile create mode 100644 arch/x86/um/nommu/do_syscall_64.c create mode 100644 arch/x86/um/nommu/entry_64.S create mode 100644 arch/x86/um/nommu/os-Linux/Makefile create mode 100644 arch/x86/um/nommu/os-Linux/mcontext.c create mode 100644 arch/x86/um/nommu/syscalls.h create mode 100644 arch/x86/um/nommu/syscalls_64.c base-commit: 68e25613ed4d06c987a42b0589f54ce88c13477c -- 2.43.0