LoongArch: BPF: Align value-returning atomics with LKMM

Per the Linux Kernel Memory Model, value-returning atomic RMW operations
must provide sequentially consistent ordering (a full memory barrier).
On LoongArch, plain AMO instructions and bare ll/sc loops do not satisfy
this requirement by themselves.

Update emit_atomic_rmw() to emit barrier-carrying instructions for all
value-returning BPF atomics:

 - BPF_FETCH (ADD/AND/OR/XOR): use am*_db.{b,h,w,d}
 - BPF_XCHG: use amswap_db.{b,h,w,d}
 - BPF_CMPXCHG: emit dbar 0x700 after the ll/sc loop, matching
   __WEAK_LLSC_MB in cmpxchg.h

Add the corresponding instruction encodings and emit helpers to inst.h.
Non-value-returning RMW ops (plain BPF_ADD, BPF_AND, etc.) are left as
weakly ordered, consistent with LKMM.

Acked-by: Hengqi Chen <hengqi.chen@gmail.com>
Acked-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Tested-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Chenguang Zhao <zhaochenguang@kylinos.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

0 files changed, 0 insertions, 0 deletions