[PATCH bpf] riscv, bpf: make some atomic operations fully ordered

From: Puranjay Mohan <puranjay@kernel.org>
To: "Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Andrii Nakryiko" <andrii@kernel.org>,
	"Martin KaFai Lau" <martin.lau@linux.dev>,
	"Eduard Zingerman" <eddyz87@gmail.com>,
	"Song Liu" <song@kernel.org>,
	"Yonghong Song" <yonghong.song@linux.dev>,
	"John Fastabend" <john.fastabend@gmail.com>,
	"KP Singh" <kpsingh@kernel.org>,
	"Stanislav Fomichev" <sdf@google.com>,
	"Hao Luo" <haoluo@google.com>, "Jiri Olsa" <jolsa@kernel.org>,
	"Björn Töpel" <bjorn@kernel.org>, "Pu Lehui" <pulehui@huawei.com>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	"Paul Walmsley" <paul.walmsley@sifive.com>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	bpf@vger.kernel.org, linux-riscv@lists.infradead.org,
	linux-kernel@vger.kernel.org
Cc: puranjay12@gmail.com
Subject: [PATCH bpf] riscv, bpf: make some atomic operations fully ordered
Date: Sun,  5 May 2024 20:16:33 +0000	[thread overview]
Message-ID: <20240505201633.123115-1-puranjay@kernel.org> (raw)

The BPF atomic operations with the BPF_FETCH modifier along with
BPF_XCHG and BPF_CMPXCHG are fully ordered but the RISC-V JIT implements
all atomic operations except BPF_CMPXCHG with relaxed ordering.

Section 8.1 of the "The RISC-V Instruction Set Manual Volume I:
Unprivileged ISA" [1], titled, "Specifying Ordering of Atomic
Instructions" says:

| To provide more efficient support for release consistency [5], each
| atomic instruction has two bits, aq and rl, used to specify additional
| memory ordering constraints as viewed by other RISC-V harts.

and

| If only the aq bit is set, the atomic memory operation is treated as
| an acquire access.
| If only the rl bit is set, the atomic memory operation is treated as a
| release access.
|
| If both the aq and rl bits are set, the atomic memory operation is
| sequentially consistent.

Fix this by setting both aq and rl bits as 1 for operations with
BPF_FETCH and BPF_XCHG.

[1] https://riscv.org/wp-content/uploads/2017/05/riscv-spec-v2.2.pdf

Fixes: dd642ccb45ec ("riscv, bpf: Implement more atomic operations for RV64")
Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
---
 arch/riscv/net/bpf_jit_comp64.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
index ec9d692838fc..fb5d1950042b 100644
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -498,33 +498,33 @@ static void emit_atomic(u8 rd, u8 rs, s16 off, s32 imm, bool is64,
 		break;
 	/* src_reg = atomic_fetch_<op>(dst_reg + off16, src_reg) */
 	case BPF_ADD | BPF_FETCH:
-		emit(is64 ? rv_amoadd_d(rs, rs, rd, 0, 0) :
-		     rv_amoadd_w(rs, rs, rd, 0, 0), ctx);
+		emit(is64 ? rv_amoadd_d(rs, rs, rd, 1, 1) :
+		     rv_amoadd_w(rs, rs, rd, 1, 1), ctx);
 		if (!is64)
 			emit_zextw(rs, rs, ctx);
 		break;
 	case BPF_AND | BPF_FETCH:
-		emit(is64 ? rv_amoand_d(rs, rs, rd, 0, 0) :
-		     rv_amoand_w(rs, rs, rd, 0, 0), ctx);
+		emit(is64 ? rv_amoand_d(rs, rs, rd, 1, 1) :
+		     rv_amoand_w(rs, rs, rd, 1, 1), ctx);
 		if (!is64)
 			emit_zextw(rs, rs, ctx);
 		break;
 	case BPF_OR | BPF_FETCH:
-		emit(is64 ? rv_amoor_d(rs, rs, rd, 0, 0) :
-		     rv_amoor_w(rs, rs, rd, 0, 0), ctx);
+		emit(is64 ? rv_amoor_d(rs, rs, rd, 1, 1) :
+		     rv_amoor_w(rs, rs, rd, 1, 1), ctx);
 		if (!is64)
 			emit_zextw(rs, rs, ctx);
 		break;
 	case BPF_XOR | BPF_FETCH:
-		emit(is64 ? rv_amoxor_d(rs, rs, rd, 0, 0) :
-		     rv_amoxor_w(rs, rs, rd, 0, 0), ctx);
+		emit(is64 ? rv_amoxor_d(rs, rs, rd, 1, 1) :
+		     rv_amoxor_w(rs, rs, rd, 1, 1), ctx);
 		if (!is64)
 			emit_zextw(rs, rs, ctx);
 		break;
 	/* src_reg = atomic_xchg(dst_reg + off16, src_reg); */
 	case BPF_XCHG:
-		emit(is64 ? rv_amoswap_d(rs, rs, rd, 0, 0) :
-		     rv_amoswap_w(rs, rs, rd, 0, 0), ctx);
+		emit(is64 ? rv_amoswap_d(rs, rs, rd, 1, 1) :
+		     rv_amoswap_w(rs, rs, rd, 1, 1), ctx);
 		if (!is64)
 			emit_zextw(rs, rs, ctx);
 		break;
-- 
2.40.1


_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv
