Nathan reported [1] that when built with clang, the um kernel
crashes pretty much immediately. This turned out to be an issue
with the inline assembly I had added, when clang used %rax/%eax
for both operands. Reorder it so current->thread.segv_continue
is written first, and then the lifetime of _faulted won't have
overlap with the lifetime of segv_continue.

In the email thread Benjamin also pointed out that current->mm
is only NULL for true kernel tasks, but we could do this for a
userspace task, so the current->thread.segv_continue logic must
be lifted out of the mm==NULL check.

Finally, while looking at this, put a barrier() so the NULL
assignment to thread.segv_continue cannot be reorder before
the possibly faulting operation.

Reported-by: Nathan Chancellor <nathan@kernel.org>
Closes: https://lore.kernel.org/r/20250402221254.GA384@ax162 [1]
Fixes: d1d7f01f7cd3 ("um: mark rodata read-only and implement _nofault accesses")
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Pull more MM updates from Andrew Morton:

 - The series "mm: fixes for fallouts from mem_init() cleanup" from Mike
   Rapoport fixes a couple of issues with the just-merged "arch, mm:
   reduce code duplication in mem_init()" series

 - The series "MAINTAINERS: add my isub-entries to MM part." from Mike
   Rapoport does some maintenance on MAINTAINERS

 - The series "remove tlb_remove_page_ptdesc()" from Qi Zheng does some
   cleanup work to the page mapping code

 - The series "mseal system mappings" from Jeff Xu permits sealing of
   "system mappings", such as vdso, vvar, vvar_vclock, vectors (arm
   compat-mode), sigpage (arm compat-mode)

 - Plus the usual shower of singleton patches

* tag 'mm-stable-2025-04-02-22-07' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (31 commits)
  mseal sysmap: add arch-support txt
  mseal sysmap: enable s390
  selftest: test system mappings are sealed
  mseal sysmap: update mseal.rst
  mseal sysmap: uprobe mapping
  mseal sysmap: enable arm64
  mseal sysmap: enable x86-64
  mseal sysmap: generic vdso vvar mapping
  selftests: x86: test_mremap_vdso: skip if vdso is msealed
  mseal sysmap: kernel config and header change
  mm: pgtable: remove tlb_remove_page_ptdesc()
  x86: pgtable: convert to use tlb_remove_ptdesc()
  riscv: pgtable: unconditionally use tlb_remove_ptdesc()
  mm: pgtable: convert some architectures to use tlb_remove_ptdesc()
  mm: pgtable: change pt parameter of tlb_remove_ptdesc() to struct ptdesc*
  mm: pgtable: make generic tlb_remove_table() use struct ptdesc
  microblaze/mm: put mm_cmdline_setup() in .init.text section
  mm/memory_hotplug: fix call folio_test_large with tail page in do_migrate_range
  MAINTAINERS: mm: add entry for secretmem
  MAINTAINERS: mm: add entry for numa memblocks and numa emulation
  ...

Now, the nine architectures of csky, hexagon, loongarch, m68k, mips,
nios2, openrisc, sh and um do not select CONFIG_MMU_GATHER_RCU_TABLE_FREE,
and just call pagetable_dtor() + tlb_remove_page_ptdesc() (the wrapper of
tlb_remove_page()).  This is the same as the implementation of
tlb_remove_{ptdesc|table}() under !CONFIG_MMU_GATHER_TABLE_FREE, so
convert these architectures to use tlb_remove_ptdesc().

The ultimate goal is to make the architecture only use tlb_remove_ptdesc()
or tlb_remove_table() for page table pages.

[zhengqi.arch@bytedance.com: v2]
  Link: https://lkml.kernel.org/r/20250303072603.45423-1-zhengqi.arch@bytedance.com
[akpm@linux-foundation.org: remove trailing semi in arch/loongarch/include/asm/pgalloc.h]
Link: https://lkml.kernel.org/r/19db3e8673b67bad2f1df1ab37f1c89d99eacfea.1740454179.git.zhengqi.arch@bytedance.com
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Kevin Brodsky <kevin.brodsky@arm.com>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>	[m68k]
Cc: Alexandre Ghiti <alexghiti@rivosinc.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickens <hughd@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Matthew Wilcow (Oracle) <willy@infradead.org>
Cc: "Mike Rapoport (IBM)" <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

The file arch/x86/um/asm/module.h is equivalent to the definition of
asm-generic.  Thus this commit cleans up to use it.

Signed-off-by: Hajime Tazaki <thehajime@gmail.com>
Link: https://patch.msgid.link/2d70a0ed79ee0a0bef80ad4790063f4833dd9bed.1737348399.git.thehajime@gmail.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Mark read-only data actually read-only (simple mprotect), and
to be able to test it also implement _nofault accesses. This
works by setting up a new "segv_continue" pointer in current,
and then when we hit a segfault we change the signal return
context so that we continue at that address. The code using
this sets it up so that it jumps to a label and then aborts
the access that way, returning -EFAULT.

It's possible to optimize the ___backtrack_faulted() thing by
using asm goto (compiler version dependent) and/or gcc's (not
sure if clang has it) &&label extension, but at least in one
attempt I made the && caused the compiler to not load -EFAULT
into the register in case of jumping to the &&label from the
fault handler. So leave it like this for now.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Co-developed-by: Benjamin Berg <benjamin.berg@intel.com>
Signed-off-by: Benjamin Berg <benjamin.berg@intel.com>
Link: https://patch.msgid.link/20250210160926.420133-2-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Pull UML updates from Richard Weinberger:

 - hostfs: Convert to writepages

 - many cleanups: removal of dead macros, missing __init

* tag 'uml-for-linus-6.14-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/uml/linux:
  um: Remove unused asm/archparam.h header
  um: Include missing headers in asm/pgtable.h
  hostfs: Convert to writepages
  um: rtc: use RTC time when calculating the alarm
  um: Remove unused user_context function
  um: Remove unused THREAD_NAME_LEN macro
  um: Remove unused PGD_BOUND macro
  um: Mark setup_env_path as __init
  um: Mark install_fatal_handler as __init
  um: Mark set_stklim as __init
  um: Mark get_top_address as __init
  um: Mark parse_cache_line as __init
  um: Mark parse_host_cpu_flags as __init
  um: Count iomem_size only once in physmem calculation
  um: Remove obsolete fixmap support
  um: Remove unused MODULES_LEN macro

The pagetable_p*_dtor() are exactly the same except for the handling of
ptlock.  If we make ptlock_free() handle the case where ptdesc->ptl is
NULL and remove VM_BUG_ON_PAGE() from pmd_ptlock_free(), we can unify
pagetable_p*_dtor() into one function.  Let's introduce pagetable_dtor()
to do this.

Later, pagetable_dtor() will be moved to tlb_remove_ptdesc(), so that
ptlock and page table pages can be freed together (regardless of whether
RCU is used).  This prevents the use-after-free problem where the ptlock
is freed immediately but the page table pages is freed later via RCU.

Link: https://lkml.kernel.org/r/47f44fff9dc68d9d9e9a0d6c036df275f820598a.1736317725.git.zhengqi.arch@bytedance.com
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Originally-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Kevin Brodsky <kevin.brodsky@arm.com>
Acked-by: Alexander Gordeev <agordeev@linux.ibm.com>	[s390]
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Alexandre Ghiti <alexghiti@rivosinc.com>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Formerly, asm/pgtable.h relied on the implicit inclusion of asm/page.h
and linux/mm_types.h via asm/fixmap.h. With the removal of asm/fixmap.h,
these headers need to be included explicitly in asm/pgtable.h now.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202501131814.E6CxjulL-lkp@intel.com/
Fixes: 5bfc4a3a0af3 ("um: Remove obsolete fixmap support")
Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20250113153218.3331321-2-tiwei.btw@antgroup.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

It was added to support highmem. But since the highmem support has
been removed by commit a98a6d864d3b ("um: Remove broken highmem
support"), it is no longer needed. Remove it to simplify the code.

Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20241128081939.2216246-3-tiwei.btw@antgroup.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

It's not used anywhere. And its definition doesn't seem right.

Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>
Link: https://patch.msgid.link/20241128081939.2216246-2-tiwei.btw@antgroup.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>