[PATCH v8 0/4] arm64: vdso: Implement __vdso_futex_robust_try_unlock()

Hi folks,

This is my take on implementing the new vDSO for unlocking a robust futex in
arm64. If you don't know what's that, Thomas wrote a good summary,
including the motivation for this work and the x86 implementation:

   https://lore.kernel.org/lkml/878qb89g7b.ffs@tglx/

* Testing

There's one selftest proposed [1] that tests precisely if the task is
interrupted during the critical section, if the kernel will clear op_pending
pointer. I've adapted to arm64 [2] and it works as expected. This test is not
being upstreamed right now because it depends on a better way to expose
vdso.so.dbg [3].

I also used gdb to manually check if the address is cleared when the kernel
interrupts the critical section.

Thanks!
	André

[1] https://lore.kernel.org/lkml/[email protected]/
[2] https://lore.kernel.org/lkml/[email protected]/
[3] https://lore.kernel.org/lkml/[email protected]/

Changes in v8:
- Fix build when CONFIG_FUTEX is disabled
- v7: https://patch.msgid.link/[email protected]

Changes in v7:
- vdso32: Use stlex instead of strex to ensure release semanthics
- vdso32: result reg should use "=&r" clobber
- both: pop_reg will be read afterwards so it was moved to be an input operand,
  with "+Q" clobber"
v6: https://patch.msgid.link/[email protected]

Changes in v6:
- Reorganized the patchset, better split for helpers functions vs aarch64 vs
arm32 code
- Use "full name" for labels instead of macros
- Completely reworded "Implement __vdso_futex_robust_try_unlock()" to make it
more obvious what's the bug and how does this fix it
v5: https://patch.msgid.link/[email protected]

Changes in v5:
 - Drop unneeded commit "arm64/entry: Unify user mode handling"
 - Replace "_success" with "_start" labels in vdso_futex_robust_unlock_update_ips
 - Added "cc" to the asm clobberlist
v4: https://patch.msgid.link/[email protected]

Changes in v4:
 - Added commit "arm64/entry: Unify user mode handling"
 - Added missing ifdef FUTEX_ROBUST_UNLOCK guards
 - Fixed the position of _start and _success labels in the critical section
 - Instead of checking the zero flag, check the result register to decide if the
 op_pending needs to be cleared
v3: https://patch.msgid.link/[email protected]

Changes in v3:
 - Change asm to always use x2 to store *pop
 - Fix clang asm errors
 - Moved 32 bit entry point to vdso32/ and use littlearm asm
 - Adapted Sebastians test for arm
v2: https://patch.msgid.link/[email protected]

Changes in v2:
 - s/CONFIG_COMPAT/CONFIG_COMPAT_VDSO (Thomas Weißschuh)
 - Fixed linker not finding the symbols (Thomas Weißschuh)
v1: https://patch.msgid.link/[email protected]

---
André Almeida (4):
      arm64: vdso: Prepare for robust futex unlock support
      arm64: vdso: Implement __vdso_futex_robust_try_unlock()
      arm64: vdso32: Bring vdso32-offsets.h back
      arm64: vdso32: Implement __vdso_futex_robust_try_unlock()

 arch/arm64/Kconfig                    |  1 +
 arch/arm64/Makefile                   |  2 +-
 arch/arm64/include/asm/futex_robust.h | 19 +++++++++++++
 arch/arm64/include/asm/vdso.h         |  3 ++
 arch/arm64/kernel/vdso.c              | 53 ++++++++++++++++++++++++++++++++++-
 arch/arm64/kernel/vdso/Makefile       | 10 +++++++
 arch/arm64/kernel/vdso/vdso.lds.S     |  9 ++++++
 arch/arm64/kernel/vdso/vfutex.c       | 35 +++++++++++++++++++++++
 arch/arm64/kernel/vdso32/Makefile     | 12 ++++++++
 arch/arm64/kernel/vdso32/vdso.lds.S   |  9 ++++++
 arch/arm64/kernel/vdso32/vfutex.c     | 34 ++++++++++++++++++++++
 11 files changed, 185 insertions(+), 2 deletions(-)
---
base-commit: 2be02a7c996aa733bb36e29e07715621b0de9736
change-id: 20260416-tonyk-robust_arm-54ff77d2c4e4

Best regards,
--  
André Almeida <[email protected]>