* [PATCH v1 1/2] LoongArch: BPF: Support internal-only MOV to resolve per-CPU addrs
2026-06-09 4:14 [PATCH v1 0/2] LoongArch: BPF: per-CPU addr MOV and timed may_goto George Guo
@ 2026-06-09 4:14 ` George Guo
2026-06-09 4:14 ` [PATCH v1 2/2] LoongArch: BPF: Add timed may_goto support George Guo
2026-06-13 3:09 ` [PATCH v1 0/2] LoongArch: BPF: per-CPU addr MOV and timed may_goto Huacai Chen
2 siblings, 0 replies; 5+ messages in thread
From: George Guo @ 2026-06-09 4:14 UTC (permalink / raw)
To: Huacai Chen, Tiezhu Yang, Hengqi Chen
Cc: WANG Xuerui, Alexei Starovoitov, Daniel Borkmann,
Andrii Nakryiko, Martin KaFai Lau, Eduard Zingerman,
Kumar Kartikeya Dwivedi, Song Liu, Yonghong Song, Jiri Olsa,
loongarch, bpf, linux-kernel, George Guo
From: George Guo <guodongtai@kylinos.cn>
Support the internal-only BPF_MOV instruction that resolves the absolute
address of per-CPU data from its per-CPU offset. This instruction is used
only for internal inlining optimizations between the BPF verifier and the
JITs (e.g. inlining bpf_get_smp_processor_id() and per-CPU map lookups),
and is not exposed to BPF users.
LoongArch keeps the per-CPU offset of the current CPU in $r21
(__my_cpu_offset), so resolving a per-CPU address only requires adding
$r21 to the source register holding the per-CPU offset. Advertise the
capability via bpf_jit_supports_percpu_insn().
Signed-off-by: George Guo <guodongtai@kylinos.cn>
---
arch/loongarch/include/asm/inst.h | 1 +
arch/loongarch/net/bpf_jit.c | 14 ++++++++++++++
2 files changed, 15 insertions(+)
diff --git a/arch/loongarch/include/asm/inst.h b/arch/loongarch/include/asm/inst.h
index 76b723590023..44fb5ad26d1a 100644
--- a/arch/loongarch/include/asm/inst.h
+++ b/arch/loongarch/include/asm/inst.h
@@ -404,6 +404,7 @@ enum loongarch_gpr {
LOONGARCH_GPR_T6,
LOONGARCH_GPR_T7,
LOONGARCH_GPR_T8,
+ LOONGARCH_GPR_U0 = 21, /* Kernel per-CPU base register ($r21) */
LOONGARCH_GPR_FP = 22,
LOONGARCH_GPR_S0 = 23,
LOONGARCH_GPR_S1,
diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
index 24913dc7f4e8..20d5bf792108 100644
--- a/arch/loongarch/net/bpf_jit.c
+++ b/arch/loongarch/net/bpf_jit.c
@@ -728,6 +728,15 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx, bool ext
move_reg(ctx, dst, t1);
break;
}
+ if (insn_is_mov_percpu_addr(insn)) {
+ if (dst != src)
+ move_reg(ctx, dst, src);
+#ifdef CONFIG_SMP
+ /* dst += __my_cpu_offset, held in $r21 */
+ emit_insn(ctx, addd, dst, dst, LOONGARCH_GPR_U0);
+#endif
+ break;
+ }
switch (off) {
case 0:
move_reg(ctx, dst, src);
@@ -2362,6 +2371,11 @@ bool bpf_jit_supports_fsession(void)
return true;
}
+bool bpf_jit_supports_percpu_insn(void)
+{
+ return true;
+}
+
/* Indicate the JIT backend supports mixing bpf2bpf and tailcalls. */
bool bpf_jit_supports_subprog_tailcalls(void)
{
--
2.25.1
^ permalink raw reply [flat|nested] 5+ messages in thread* [PATCH v1 2/2] LoongArch: BPF: Add timed may_goto support
2026-06-09 4:14 [PATCH v1 0/2] LoongArch: BPF: per-CPU addr MOV and timed may_goto George Guo
2026-06-09 4:14 ` [PATCH v1 1/2] LoongArch: BPF: Support internal-only MOV to resolve per-CPU addrs George Guo
@ 2026-06-09 4:14 ` George Guo
2026-06-13 3:09 ` [PATCH v1 0/2] LoongArch: BPF: per-CPU addr MOV and timed may_goto Huacai Chen
2 siblings, 0 replies; 5+ messages in thread
From: George Guo @ 2026-06-09 4:14 UTC (permalink / raw)
To: Huacai Chen, Tiezhu Yang, Hengqi Chen
Cc: WANG Xuerui, Alexei Starovoitov, Daniel Borkmann,
Andrii Nakryiko, Martin KaFai Lau, Eduard Zingerman,
Kumar Kartikeya Dwivedi, Song Liu, Yonghong Song, Jiri Olsa,
loongarch, bpf, linux-kernel, George Guo
From: George Guo <guodongtai@kylinos.cn>
Implement arch_bpf_timed_may_goto() and advertise it through
bpf_jit_supports_timed_may_goto() so the verifier lowers may_goto into
the timed variant: instead of a fixed iteration counter, the loop is
bounded by a wall-clock timeout maintained in a per-loop stack slot.
arch_bpf_timed_may_goto() is called with a custom calling convention.
The verifier passes the stack offset of the count/timestamp pair in
BPF_REG_AX ($t0) and expects the updated count back in the same
register, so the stub adds the offset to BPF_REG_FP ($s4), calls
bpf_check_timed_may_goto(), and moves the result back into $t0 while
preserving the BPF caller-saved registers R0 - R5. The JIT call path is
updated to skip the usual 'BPF_REG_0 = C return value' move for this
helper since its result is delivered in BPF_REG_AX instead.
Signed-off-by: George Guo <guodongtai@kylinos.cn>
---
arch/loongarch/net/Makefile | 2 +-
arch/loongarch/net/bpf_jit.c | 13 ++++++-
arch/loongarch/net/bpf_timed_may_goto.S | 47 +++++++++++++++++++++++++
3 files changed, 60 insertions(+), 2 deletions(-)
create mode 100644 arch/loongarch/net/bpf_timed_may_goto.S
diff --git a/arch/loongarch/net/Makefile b/arch/loongarch/net/Makefile
index 1ec12a0c324a..8d9ddb48f9ea 100644
--- a/arch/loongarch/net/Makefile
+++ b/arch/loongarch/net/Makefile
@@ -4,4 +4,4 @@
#
# Copyright (C) 2022 Loongson Technology Corporation Limited
#
-obj-$(CONFIG_BPF_JIT) += bpf_jit.o
+obj-$(CONFIG_BPF_JIT) += bpf_jit.o bpf_timed_may_goto.o
diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
index 20d5bf792108..794c0c37fa9c 100644
--- a/arch/loongarch/net/bpf_jit.c
+++ b/arch/loongarch/net/bpf_jit.c
@@ -1185,7 +1185,13 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx, bool ext
move_addr(ctx, t1, func_addr);
emit_insn(ctx, jirl, LOONGARCH_GPR_RA, t1, 0);
- if (insn->src_reg != BPF_PSEUDO_CALL)
+ /*
+ * Call to arch_bpf_timed_may_goto() uses a custom calling
+ * convention with the argument and return value in BPF_REG_AX,
+ * so skip moving the C return value into BPF_REG_0.
+ */
+ if (insn->src_reg != BPF_PSEUDO_CALL &&
+ func_addr != (u64)arch_bpf_timed_may_goto)
move_reg(ctx, regmap[BPF_REG_0], LOONGARCH_GPR_A0);
break;
@@ -2376,6 +2382,11 @@ bool bpf_jit_supports_percpu_insn(void)
return true;
}
+bool bpf_jit_supports_timed_may_goto(void)
+{
+ return true;
+}
+
/* Indicate the JIT backend supports mixing bpf2bpf and tailcalls. */
bool bpf_jit_supports_subprog_tailcalls(void)
{
diff --git a/arch/loongarch/net/bpf_timed_may_goto.S b/arch/loongarch/net/bpf_timed_may_goto.S
new file mode 100644
index 000000000000..aa86250a9c65
--- /dev/null
+++ b/arch/loongarch/net/bpf_timed_may_goto.S
@@ -0,0 +1,47 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Author: George Guo <guodongtai@kylinos.cn>
+ * Copyright (C) 2026 KylinSoft Corporation.
+ */
+
+#include <asm/asmmacro.h>
+#include <asm/regdef.h>
+#include <linux/export.h>
+#include <linux/linkage.h>
+
+SYM_FUNC_START(arch_bpf_timed_may_goto)
+ addi.d sp, sp, -64
+ st.d ra, sp, 0
+
+ /* Save BPF registers R0 - R5 (a5, a0 - a4) */
+ st.d a5, sp, 8
+ st.d a0, sp, 16
+ st.d a1, sp, 24
+ st.d a2, sp, 32
+ st.d a3, sp, 40
+ st.d a4, sp, 48
+
+ /*
+ * BPF_REG_AX (t0) holds the offset passed in by the verifier; add it
+ * to BPF_REG_FP (s4) to get the pointer to the count and timestamp,
+ * then pass it as the first argument in a0.
+ *
+ * The verifier emits a load using FP right before this call, so
+ * BPF_REG_FP (s4) is always set up by the JIT in this case.
+ */
+ add.d a0, t0, s4
+ bl bpf_check_timed_may_goto
+ /* BPF_REG_AX (t0) will be stored into count, so move the return value to it. */
+ move t0, a0
+
+ ld.d ra, sp, 0
+ ld.d a5, sp, 8
+ ld.d a0, sp, 16
+ ld.d a1, sp, 24
+ ld.d a2, sp, 32
+ ld.d a3, sp, 40
+ ld.d a4, sp, 48
+ addi.d sp, sp, 64
+
+ jr ra
+SYM_FUNC_END(arch_bpf_timed_may_goto)
--
2.25.1
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH v1 0/2] LoongArch: BPF: per-CPU addr MOV and timed may_goto
2026-06-09 4:14 [PATCH v1 0/2] LoongArch: BPF: per-CPU addr MOV and timed may_goto George Guo
2026-06-09 4:14 ` [PATCH v1 1/2] LoongArch: BPF: Support internal-only MOV to resolve per-CPU addrs George Guo
2026-06-09 4:14 ` [PATCH v1 2/2] LoongArch: BPF: Add timed may_goto support George Guo
@ 2026-06-13 3:09 ` Huacai Chen
2026-06-15 9:08 ` Tiezhu Yang
2 siblings, 1 reply; 5+ messages in thread
From: Huacai Chen @ 2026-06-13 3:09 UTC (permalink / raw)
To: George Guo
Cc: Tiezhu Yang, Hengqi Chen, WANG Xuerui, Alexei Starovoitov,
Daniel Borkmann, Andrii Nakryiko, Martin KaFai Lau,
Eduard Zingerman, Kumar Kartikeya Dwivedi, Song Liu,
Yonghong Song, Jiri Olsa, loongarch, bpf, linux-kernel,
George Guo
Hi, Tiezhu and Hengqi,
Any comments about this series?
Huacai
On Tue, Jun 9, 2026 at 12:14 PM George Guo <dongtai.guo@linux.dev> wrote:
>
> From: George Guo <guodongtai@kylinos.cn>
>
> This series enables two independent BPF JIT features on LoongArch, each
> advertised to the verifier via the corresponding bpf_jit_supports_*()
> hook:
>
> Patch 1 implements the internal-only BPF_MOV that resolves a per-CPU
> address from its per-CPU offset. LoongArch keeps the current CPU's
> per-CPU offset in $r21 (__my_cpu_offset), so the resolution is a single
> add of $r21 to the source register. This is used by verifier/JIT
> inlining (e.g. bpf_get_smp_processor_id() and per-CPU map lookups) and
> is not exposed to BPF users.
>
> Patch 2 implements arch_bpf_timed_may_goto() (in a small assembly stub
> with a custom calling convention passing the count/timestamp slot offset
> in BPF_REG_AX) and advertises it, so the verifier lowers may_goto into
> the timed, wall-clock-bounded variant instead of a fixed iteration
> counter.
>
> Tested on a LoongArch (Loongson-3A5000) QEMU/KVM guest with
> CONFIG_PAGE_SIZE_16KB and CONFIG_UNWINDER_ORC:
> - patch 1: test_progs cpumask and percpu map cases pass;
> - patch 2: test_progs iters (incl. the cond_break / may_goto loop
> cases) all pass.
>
> George Guo (2):
> LoongArch: BPF: Support internal-only MOV to resolve per-CPU addrs
> LoongArch: BPF: Add timed may_goto support
>
> arch/loongarch/include/asm/inst.h | 1 +
> arch/loongarch/net/Makefile | 2 +-
> arch/loongarch/net/bpf_jit.c | 27 ++++++++++++++-
> arch/loongarch/net/bpf_timed_may_goto.S | 44 +++++++++++++++++++++++++
> 4 files changed, 72 insertions(+), 2 deletions(-)
> create mode 100644 arch/loongarch/net/bpf_timed_may_goto.S
>
> --
> 2.25.1
>
^ permalink raw reply [flat|nested] 5+ messages in thread