This is a note to let you know that I've just added the patch titled
riscv, bpf: make some atomic operations fully ordered
to the 6.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
riscv-bpf-make-some-atomic-operations-fully-ordered.patch
and it can be found in the queue-6.8 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit ee9e2b4209da785d198e052ecfc1e5f70e4217c8
Author: Puranjay Mohan <puranjay@xxxxxxxxxx>
Date: Sun May 5 20:16:33 2024 +0000
riscv, bpf: make some atomic operations fully ordered
[ Upstream commit 20a759df3bba35bf5c3ddec0c02ad69b603b584c ]
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@xxxxxxxxxx>
Reviewed-by: Pu Lehui <pulehui@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20240505201633.123115-1-puranjay@xxxxxxxxxx
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
index 0bd747d1d00fc..29f031f68f480 100644
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -516,33 +516,33 @@ 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_zext_32(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_zext_32(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_zext_32(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_zext_32(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_zext_32(rs, ctx);
break;
