[PATCH bpf-next 2/3] bpf, x86: Don't generate lock prefix for BPF_XCHG

[Hou Tao <houtao@xxxxxxxxxxxxxxx>]

From: Hou Tao <houtao1@xxxxxxxxxx>

According to the implementation of atomic_xchg() under x86-64, the lock
prefix is not necessary for BPF_XCHG atomic operation, so just remove
it.

Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>
---
 arch/x86/net/bpf_jit_comp.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index c89a4abdd726..49dac4d22a7b 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -990,7 +990,9 @@ static int emit_atomic(u8 **pprog, u8 atomic_op,
 {
 	u8 *prog = *pprog;
 
-	EMIT1(0xF0); /* lock prefix */
+	/* lock prefix */
+	if (atomic_op != BPF_XCHG)
+		EMIT1(0xF0);
 
 	maybe_emit_mod(&prog, dst_reg, src_reg, bpf_size == BPF_DW);
 
-- 
2.29.2