lwn.git/arch/x86/um, branch docs-mw

Merge tag 'uml-for-7.1-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/uml/linux

2026-04-20T23:36:46+00:00

Pull uml updates from Johannes Berg: "Mostly cleanups and small things, notably: - musl libc compatibility - vDSO installation fix - TLB sync race fix for recent SMP support - build fix for 32-bit with Clang 20/21" * tag 'uml-for-7.1-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/uml/linux: um: Disable GCOV_PROFILE_ALL on 32-bit UML with Clang 20/21 um: drivers: call kernel_strrchr() explicitly in cow_user.c um: Replace strncpy() with strnlen()+memcpy_and_pad() in strncpy_chunk_from_user() x86/um: fix vDSO installation um: Remove CONFIG_FRAME_WARN from x86_64_defconfig um: Fix pte_read() and pte_exec() for kernel mappings um: Fix potential race condition in TLB sync um: time-travel: clean up kernel-doc warnings um: avoid struct sigcontext redefinition with musl um: fix address-of CMSG_DATA() rvalue in stub

mm: convert do_brk_flags() to use vma_flags_t

2026-04-05T20:53:40+00:00

In order to be able to do this, we need to change VM_DATA_DEFAULT_FLAGS and friends and update the architecture-specific definitions also. We then have to update some KSM logic to handle VMA flags, and introduce VMA_STACK_FLAGS to define the vma_flags_t equivalent of VM_STACK_FLAGS. We also introduce two helper functions for use during the time we are converting legacy flags to vma_flags_t values - vma_flags_to_legacy() and legacy_to_vma_flags(). This enables us to iteratively make changes to break these changes up into separate parts. We use these explicitly here to keep VM_STACK_FLAGS around for certain users which need to maintain the legacy vm_flags_t values for the time being. We are no longer able to rely on the simple VM_xxx being set to zero if the feature is not enabled, so in the case of VM_DROPPABLE we introduce VMA_DROPPABLE as the vma_flags_t equivalent, which is set to EMPTY_VMA_FLAGS if the droppable flag is not available. While we're here, we make the description of do_brk_flags() into a kdoc comment, as it almost was already. We use vma_flags_to_legacy() to not need to update the vm_get_page_prot() logic as this time. Note that in create_init_stack_vma() we have to replace the BUILD_BUG_ON() with a VM_WARN_ON_ONCE() as the tested values are no longer build time available. We also update mprotect_fixup() to use VMA flags where possible, though we have to live with a little duplication between vm_flags_t and vma_flags_t values for the time being until further conversions are made. While we're here, update VM_SPECIAL to be defined in terms of VMA_SPECIAL_FLAGS now we have vma_flags_to_legacy(). Finally, we update the VMA tests to reflect these changes. Link: https://lkml.kernel.org/r/d02e3e45d9a33d7904b149f5604904089fd640ae.1774034900.git.ljs@kernel.org Signed-off-by: Lorenzo Stoakes (Oracle) Acked-by: Paul Moore [SELinux] Acked-by: Vlastimil Babka (SUSE) Cc: Albert Ou Cc: Alexander Gordeev Cc: Alexandre Ghiti Cc: Al Viro Cc: Anton Ivanov Cc: "Borislav Petkov (AMD)" Cc: Catalin Marinas Cc: Chengming Zhou Cc: Christian Borntraeger Cc: Christian Brauner Cc: David Hildenbrand Cc: Dinh Nguyen Cc: Heiko Carstens Cc: "H. Peter Anvin" Cc: Huacai Chen Cc: Ingo Molnar Cc: Jan Kara Cc: Jann Horn Cc: Johannes Berg Cc: Kees Cook Cc: Liam Howlett Cc: Madhavan Srinivasan Cc: Michael Ellerman Cc: Michal Hocko Cc: Mike Rapoport Cc: Nicholas Piggin Cc: Ondrej Mosnacek Cc: Palmer Dabbelt Cc: Pedro Falcato Cc: Richard Weinberger Cc: Russell King Cc: Stephen Smalley Cc: Suren Baghdasaryan Cc: Sven Schnelle Cc: Thomas Bogendoerfer Cc: Vasily Gorbik Cc: Vineet Gupta Cc: WANG Xuerui Cc: Will Deacon Cc: xu xin Signed-off-by: Andrew Morton

x86/um: fix vDSO installation

2026-03-21T09:43:21+00:00

The generic vDSO installation logic used by 'make vdso_install' requires that $(vdso-install-y) is defined by the top-level architecture Makefile and that it contains a path relative to the root of the tree. For UML neither of these is satisfied. Move the definition of $(vdso-install-y) to a place which is included by the arch/um/Makefile and use the full relative path. Fixes: f1c2bb8b9964 ("um: implement a x86_64 vDSO") Signed-off-by: Thomas Weißschuh Link: https://patch.msgid.link/20260318-um-vdso-install-v1-1-26a4ca5c4210@weissschuh.net Signed-off-by: Johannes Berg

um: avoid struct sigcontext redefinition with musl

2026-03-21T09:41:44+00:00

mcontext.c includes both and . With musl libc, this causes a struct sigcontext redefinition error: pulls in musl's , which defines struct sigcontext directly. The kernel's then provides a second, conflicting definition of the same struct. With glibc this does not conflict because glibc's signal headers source their struct sigcontext from the kernel's own UAPI headers, so the include guard in makes the second inclusion a no-op. mcontext.c does not actually use struct sigcontext by name -- it only needs the FP-state types (_fpstate, _xstate, etc.) that are defined in independently of the sigcontext struct. Temporarily rename sigcontext to __kernel_sigcontext during the inclusion of so that the kernel's definition does not collide with musl's. The #undef restores normal name resolution immediately afterward. No functional change with glibc; fixes the build with musl. Signed-off-by: Marcel W. Wysocki Link: https://patch.msgid.link/20260215142803.1455757-2-maci.stgn@gmail.com Signed-off-by: Johannes Berg

arch: um/x86: Select ARCH_SUPPORTS_ATOMIC_RMW for UML_X86

2026-01-09T11:01:41+00:00

x86 atomic instructions are used for um on UML_X86, therefore atomics on UML_X86 support native atomic RmW as x86 does, hence select ARCH_SUPPORTS_ATOMIC_RMW. Reviewed-by: FUJITA Tomonori Acked-by: Richard Weinberger Signed-off-by: Boqun Feng Link: https://patch.msgid.link/20260106034034.60074-1-boqun.feng@gmail.com

um: Always set up AT_HWCAP and AT_PLATFORM

2025-11-06T12:02:34+00:00

Historically the code to set up AT_HWCAP and AT_PLATFORM was only built for 32bit x86 as it was intermingled with the vDSO passthrough code. Now that vDSO passthrough has been removed, always pass through AT_HWCAP and AT_PLATFORM. Signed-off-by: Thomas Weißschuh Link: https://patch.msgid.link/20251028-uml-remove-32bit-pseudo-vdso-v1-10-e930063eff5f@weissschuh.net Signed-off-by: Johannes Berg

x86/um: Remove FIXADDR_USER_START and FIXADDR_USE_END

2025-11-06T12:02:34+00:00

There are no users left. Signed-off-by: Thomas Weißschuh Link: https://patch.msgid.link/20251028-uml-remove-32bit-pseudo-vdso-v1-9-e930063eff5f@weissschuh.net Signed-off-by: Johannes Berg

x86/um: Drop gate area handling

2025-11-06T12:02:33+00:00

With the removal of the vDSO passthrough from the host, FIXADDR_USER_START is always 0 and the gate area setup code is dead. Remove it. Signed-off-by: Thomas Weißschuh Link: https://patch.msgid.link/20251028-uml-remove-32bit-pseudo-vdso-v1-5-e930063eff5f@weissschuh.net Signed-off-by: Johannes Berg

x86/um: Do not inherit vDSO from host

2025-11-06T12:02:33+00:00

Inheriting the vDSO from the host is problematic. The values read from the time functions will not be correct for the UML kernel. Furthermore the start and end of the vDSO are not stable or detectable by userspace. Specifically the vDSO datapages start before AT_SYSINFO_EHDR and the vDSO itself is larger than a single page. This codepath is only used on 32bit x86 UML. In my testing with both 32bit and 64bit hosts the passthrough functionality has always been disabled anyways due to the checks against envp in scan_elf_aux(). Signed-off-by: Thomas Weißschuh Link: https://patch.msgid.link/20251028-uml-remove-32bit-pseudo-vdso-v1-4-e930063eff5f@weissschuh.net Signed-off-by: Johannes Berg

x86/um: Move ELF_PLATFORM fallback to x86-specific code

2025-11-06T12:02:33+00:00

The generic UM code should not have references to x86-specific value. Move the fallback into the x86-specific header. Signed-off-by: Thomas Weißschuh Link: https://patch.msgid.link/20251028-uml-remove-32bit-pseudo-vdso-v1-2-e930063eff5f@weissschuh.net Signed-off-by: Johannes Berg