[RFC bpf-next 0/2] bpf, mips: Add BPF_MOVSX support to the JITs

[Nicholas Dudar <main.kalliope@gmail.com>]

bpf-next is closed for the merge window, so I am sending this for
review. I plan to post this series after it reopens.

The MIPS32 and MIPS64 JITs lower register BPF_MOVSX as an ordinary
move because their register-move paths do not interpret insn->off.
Negative low-width values therefore retain incorrect upper bits.

First factor ordinary register moves into backend-local 32- and 64-bit
helpers. Then handle the BPF-defined MOVSX widths from insn->off in
those helpers. This keeps the verifier-inserted ALU32 zero extension on
its existing path and preserves the MIPS32 register-pair handling. The
implementation uses shift sequences rather than the R2+ seb/seh
instructions so it also works on base MIPS32.

MOVSX can be applied before or after the in-flight SDIV/SMOD series.
Both must precede MEMSX (yet to be sent). The ordering discussion is
here:

Link: https://lore.kernel.org/bpf/CAJZwKkis=3NGw9At0WfiZaRYEoMPbQfqJKN0e+vtRDvp4VY5Ng@mail.gmail.com/

Patch 1 did not change any test_bpf result. On the four little-endian
profiles where the complete suite was run at each boundary, patch 2
fixed the ALU32 byte and halfword MOVSX cases and the ALU64 byte,
halfword, and word cases. The 32-bit totals moved from 1031 passes and
31 failures to 1036 passes and 26 failures; the 64-bit totals moved
from 1030 passes and 31 failures to 1035 passes and 26 failures. Patch
2 did not change any other test result. Ordinary MOV and zero-extension
controls passed at each boundary.

Selector-focused QEMU testing covered MIPS32 base, R2, and R6 plus
pre-R6 MIPS64, each in big- and little-endian configurations. No
physical MIPS hardware was tested.

Nicholas Dudar (2):
  bpf, mips: Factor register moves into helpers
  bpf, mips: Add support for BPF_MOVSX in the JITs

 arch/mips/net/bpf_jit_comp32.c | 54 +++++++++++++++++++++++++++++++---
 arch/mips/net/bpf_jit_comp64.c | 48 ++++++++++++++++++++++++++++--
 2 files changed, 95 insertions(+), 7 deletions(-)


base-commit: 6655c409707ec8ce9ce0850ffe4fe02331fd4d9c