[PATCH v2 0/2] x86/fpu: Fix dynamic fpstate leak on exec()

["Guixiong Wei" <weiguixiong@bytedance.com>]

An exec() after using an XFD-controlled xfeature resets fpu->fpstate to
its embedded storage without freeing the dynamically allocated state.
Fix the leak in fpstate_reset() and add an AMX regression selftest.

The fix preserves the old pointer, installs and initializes the embedded
fpstate, and then frees the detached allocation. Since fpstate_reset()
now owns cleanup, fpu_clone() initializes dst_fpu->fpstate to NULL before
invoking it.

The selftest performs ten XTILEDATA request, XRSTOR and self-exec cycles
in the same task and checks the associated /proc/vmallocinfo entries.
It fails with 10 leaked allocations on the unfixed kernel and passes
with zero on the fixed kernel.

Changes since v1:
- Rename the fix and describe the memory leak explicitly.
- Move cleanup into fpstate_reset().
- Detach the old fpstate before freeing it.
- Initialize dst_fpu->fpstate to NULL before resetting it.
- Add the requested AMX regression selftest as a separate patch.

v1: https://lore.kernel.org/r/20260929151013.81562-2-weiguixiong@bytedance.com

Guixiong Wei (2):
  x86/fpu: Fix memory leak with dynamic fpstate and exec()
  selftests/x86/amx: Test dynamic fpstate cleanup across exec()

 arch/x86/include/asm/fpu/api.h    |   6 +-
 arch/x86/kernel/fpu/core.c        |   5 ++
 arch/x86/kernel/fpu/xstate.c      |  10 +--
 arch/x86/kernel/process.c         |   2 +-
 tools/testing/selftests/x86/amx.c | 144 +++++++++++++++++++++++++++++-
 5 files changed, 156 insertions(+), 11 deletions(-)


base-commit: 72d3fcf802c45d00b300f25b848a93c3a2bd7c7e
-- 
2.50.1 (Apple Git-155)