[PATCH bpf-next v4 2/4] bpf: add bpf_cpu_cycles_to_ns helper

Vadim Fedorenko
2024-11-07T21:12:53Z

The new helper should be used to convert cycles received by
bpf_get_cpu_cycle() into nanoseconds.

Signed-off-by: Vadim Fedorenko <vadfed@meta.com>

v4:
* change helper name to bpf_cpu_cycles_to_ns.
* hide it behind CONFIG_GENERIC_GETTIMEOFDAY to avoid exposing on
unsupported architectures.
---
arch/x86/net/bpf_jit_comp.c | 22 ++++++++++++++++++++++
arch/x86/net/bpf_jit_comp32.c | 19 +++++++++++++++++++
include/linux/bpf.h | 1 +
kernel/bpf/helpers.c | 10 +++++++++-
4 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 4f78ed93ee7f..ddc73d9a90f4 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -11,6 +11,7 @@
#include <linux/bpf.h>
#include <linux/memory.h>
#include <linux/sort.h>
+#include <linux/clocksource.h>
#include <asm/extable.h>
#include <asm/ftrace.h>
#include <asm/set_memory.h>
@@ -2146,6 +2147,24 @@ st: if (is_imm8(insn->off))
break;
}

+ if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL &&
+ imm32 == BPF_CALL_IMM(bpf_cpu_cycles_to_ns) &&
+ boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) {
+ u32 mult, shift;
+
+ clocks_calc_mult_shift(&mult, &shift, tsc_khz, USEC_PER_SEC, 0);
+ /* imul RAX, RDI, mult */
+ maybe_emit_mod(&prog, BPF_REG_1, BPF_REG_0, true);
+ EMIT2_off32(0x69, add_2reg(0xC0, BPF_REG_1, BPF_REG_0),
+ mult);
+
+ /* shr RAX, shift (which is less than 64) */
+ maybe_emit_1mod(&prog, BPF_REG_0, true);
+ EMIT3(0xC1, add_1reg(0xE8, BPF_REG_0), shift);
+
+ break;
+ }
+
func = (u8 *) __bpf_call_base + imm32;
if (tail_call_reachable) {
LOAD_TAIL_CALL_CNT_PTR(bpf_prog->aux->stack_depth);
@@ -3678,5 +3697,8 @@ bool bpf_jit_inlines_kfunc_call(s32 imm)
{
if (imm == BPF_CALL_IMM(bpf_get_cpu_cycles))
return true;
+ if (imm == BPF_CALL_IMM(bpf_cpu_cycles_to_ns) &&
+ boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
+ return true;
return false;
}
diff --git a/arch/x86/net/bpf_jit_comp32.c b/arch/x86/net/bpf_jit_comp32.c
index e6097a371b69..34f762f28c82 100644
--- a/arch/x86/net/bpf_jit_comp32.c
+++ b/arch/x86/net/bpf_jit_comp32.c
@@ -12,6 +12,7 @@
#include <linux/netdevice.h>
#include <linux/filter.h>
#include <linux/if_vlan.h>
+#include <linux/clocksource.h>
#include <asm/cacheflush.h>
#include <asm/set_memory.h>
#include <asm/nospec-branch.h>
@@ -2100,6 +2101,24 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
EMIT2(0x0F, 0x31);
break;
}
+ if (imm32 == BPF_CALL_IMM(bpf_cpu_cycles_to_ns) &&
+ boot_cpu_has(X86_FEATURE_CONSTANT_TSC)) {
+ u32 mult, shift;
+
+ clocks_calc_mult_shift(&mult, &shift, tsc_khz,
+ USEC_PER_SEC, 0);
+
+ /* move parameter to BPF_REG_0 */
+ emit_ia32_mov_r64(true, bpf2ia32[BPF_REG_0],
+ bpf2ia32[BPF_REG_1], true, true,
+ &prog, bpf_prog->aux);
+ /* multiply parameter by mut */
+ emit_ia32_mul_i64(bpf2ia32[BPF_REG_0],
+ mult, true, &prog);
+ /* shift parameter by shift which is less than 64 */
+ emit_ia32_rsh_i64(bpf2ia32[BPF_REG_0],
+ shift, true, &prog);
+ }

err = emit_kfunc_call(bpf_prog,
image + addrs[i],
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index fed5f36d387a..46fa662d95e4 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -3331,6 +3331,7 @@ u64 bpf_get_raw_cpu_id(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5);
/* Inlined kfuncs */
#if IS_ENABLED(CONFIG_GENERIC_GETTIMEOFDAY)
u64 bpf_get_cpu_cycles(void);
+u64 bpf_cpu_cycles_to_ns(u64 cycles);
#endif

#if defined(CONFIG_NET)
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index c07cb058e710..d794ddc74de5 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -25,6 +25,7 @@
#include <linux/kasan.h>
#if IS_ENABLED(CONFIG_GENERIC_GETTIMEOFDAY)
#include <vdso/datapage.h>
+#include <asm/vdso/vsyscall.h>
#endif

#include "../../lib/kstrtox.h"
@@ -3031,8 +3032,14 @@ __bpf_kfunc u64 bpf_get_cpu_cycles(void)
{
return __arch_get_hw_counter(1, NULL);
}
-#endif

+__bpf_kfunc u64 bpf_cpu_cycles_to_ns(u64 cycles)
+{
+ const struct vdso_data *vd = __arch_get_k_vdso_data();
+
+ return mul_u64_u32_shr(cycles, vd->mult, vd->shift);
+}
+#endif
__bpf_kfunc_end_defs();

BTF_KFUNCS_START(generic_btf_ids)
@@ -3127,6 +3134,7 @@ BTF_ID_FLAGS(func, bpf_iter_kmem_cache_next, KF_ITER_NEXT | KF_RET_NULL | KF_SLE
BTF_ID_FLAGS(func, bpf_iter_kmem_cache_destroy, KF_ITER_DESTROY | KF_SLEEPABLE)
#ifdef IS_ENABLED(CONFIG_GENERIC_GETTIMEOFDAY)
BTF_ID_FLAGS(func, bpf_get_cpu_cycles, KF_FASTCALL)
+BTF_ID_FLAGS(func, bpf_cpu_cycles_to_ns, KF_FASTCALL)
#endif
BTF_KFUNCS_END(common_btf_ids)

--
2.43.5