diff options
| author | Uros Bizjak <ubizjak@gmail.com> | 2025-12-08 19:33:34 +0300 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2025-12-21 21:55:55 +0300 |
| commit | e09f6be4a3558e01afb4d16705ce57006a6f9712 (patch) | |
| tree | 249e41c8118b2b70c88ea6d88ddaa45409dccc42 | |
| parent | c2f2f005a1c2e2d06f07511068917fa729614c18 (diff) | |
| download | linux-e09f6be4a3558e01afb4d16705ce57006a6f9712.tar.xz | |
x86/bpf: Avoid emitting LOCK prefix for XCHG atomic ops
The x86 XCHG instruction is implicitly locked when one of the
operands is a memory location, making an explicit LOCK prefix
unnecessary.
Stop emitting the LOCK prefix for BPF_XCHG in the JIT atomic
read-modify-write helpers. This avoids redundant instruction
prefixes while preserving correct atomic semantics.
No functional change for other atomic operations.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://lore.kernel.org/r/20251208163420.7643-1-ubizjak@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
| -rw-r--r-- | arch/x86/net/bpf_jit_comp.c | 7 |
1 files changed, 5 insertions, 2 deletions
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index b0bac2a66eff..e3b1c4b1d550 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -1305,7 +1305,8 @@ static int emit_atomic_rmw(u8 **pprog, u32 atomic_op, { u8 *prog = *pprog; - EMIT1(0xF0); /* lock prefix */ + if (atomic_op != BPF_XCHG) + EMIT1(0xF0); /* lock prefix */ maybe_emit_mod(&prog, dst_reg, src_reg, bpf_size == BPF_DW); @@ -1347,7 +1348,9 @@ static int emit_atomic_rmw_index(u8 **pprog, u32 atomic_op, u32 size, { u8 *prog = *pprog; - EMIT1(0xF0); /* lock prefix */ + if (atomic_op != BPF_XCHG) + EMIT1(0xF0); /* lock prefix */ + switch (size) { case BPF_W: EMIT1(add_3mod(0x40, dst_reg, src_reg, index_reg)); |