Two bugs in the TDX guest port I/O #VE emulation, plus a small helper
extracted from KVM to avoid open-coding partial-register-write logic
in the second fix.

Patch 1 is an off-by-one in the mask used to clip the I/O value:
GENMASK(BITS_PER_BYTE * size, 0) is one bit too wide. Unchanged from
v3 1/2.

Patch 2 lifts KVM's instruction-emulator helper assign_register() out
of arch/x86/kvm/emulate.c into <asm/insn-eval.h>, renamed to
insn_assign_reg(). Dave suggested consolidating rather than adding a
third copy of the same partial-register switch; the body is rewritten
using plain arithmetic (suggested by David Laight) so the helper does
not rely on -fno-strict-aliasing or little-endian byte order. KVM
behaviour is unchanged.

Patch 3 fixes the architectural zero-extension of 32-bit IN: the old
mask-based handle_in() preserves RAX[63:32] after inl, which is wrong.
Now done by calling the helper.

Changes since v3:
  - Patch 1/2 carried over unchanged as 1/3.
  - Helper extracted from KVM (new patch 2/3) and used from
    handle_in() (Dave, David Laight).
  - Reviewed-by tags from v3 2/2 dropped on patch 3/3 because the
    implementation changed substantially. v3 1/2 -> v4 1/3 Rb tags
    preserved (patch unchanged).

v3: https://lore.kernel.org/all/20260527120544.2903923-1-kas@kernel.org/

Kiryl Shutsemau (Meta) (3):
  x86/tdx: Fix off-by-one in port I/O handling
  x86/insn-eval: Add insn_assign_reg() helper
  x86/tdx: Fix zero-extension for 32-bit port I/O

 arch/x86/coco/tdx/tdx.c          | 10 ++++------
 arch/x86/include/asm/insn-eval.h | 25 +++++++++++++++++++++++++
 arch/x86/kvm/emulate.c           | 26 ++++----------------------
 3 files changed, 33 insertions(+), 28 deletions(-)

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2.54.0