Re: [PATCH bpf-next v5 1/4] bpf: add bpf_get_cpu_cycles kfunc

[Yonghong Song <yonghong.song@linux.dev>]

On 11/8/24 4:41 PM, Vadim Fedorenko wrote:
> New kfunc to return ARCH-specific timecounter. For x86 BPF JIT converts
> it into rdtsc ordered call. Other architectures will get JIT
> implementation too if supported. The fallback is to
> __arch_get_hw_counter().
>
> Signed-off-by: Vadim Fedorenko <vadfed@meta.com>
> ---
> v4 -> v5:
> * use if instead of ifdef with IS_ENABLED
> v3 -> v4:
> * change name of the helper to bpf_get_cpu_cycles (Andrii)
> * Hide the helper behind CONFIG_GENERIC_GETTIMEOFDAY to avoid exposing
>    it on architectures which do not have vDSO functions and data
> * reduce the scope of check of inlined functions in verifier to only 2,
>    which are actually inlined.
> v2 -> v3:
> * change name of the helper to bpf_get_cpu_cycles_counter to explicitly
>    mention what counter it provides (Andrii)
> * move kfunc definition to bpf.h to use it in JIT.
> * introduce another kfunc to convert cycles into nanoseconds as more
>    meaningful time units for generic tracing use case (Andrii)
> v1 -> v2:
> * Fix incorrect function return value type to u64
> * Introduce bpf_jit_inlines_kfunc_call() and use it in
>    mark_fastcall_pattern_for_call() to avoid clobbering in case of
>    running programs with no JIT (Eduard)
> * Avoid rewriting instruction and check function pointer directly
>    in JIT (Alexei)
> * Change includes to fix compile issues on non x86 architectures
> ---
>   arch/x86/net/bpf_jit_comp.c   | 28 ++++++++++++++++++++++++++++
>   arch/x86/net/bpf_jit_comp32.c | 14 ++++++++++++++
>   include/linux/bpf.h           |  5 +++++
>   include/linux/filter.h        |  1 +
>   kernel/bpf/core.c             | 11 +++++++++++
>   kernel/bpf/helpers.c          | 13 +++++++++++++
>   kernel/bpf/verifier.c         | 30 +++++++++++++++++++++++++++++-
>   7 files changed, 101 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 06b080b61aa5..4f78ed93ee7f 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -2126,6 +2126,26 @@ st:			if (is_imm8(insn->off))
>   		case BPF_JMP | BPF_CALL: {
>   			u8 *ip = image + addrs[i - 1];
>   
> +			if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL &&
> +			    imm32 == BPF_CALL_IMM(bpf_get_cpu_cycles)) {
> +				/* Save RDX because RDTSC will use EDX:EAX to return u64 */
> +				emit_mov_reg(&prog, true, AUX_REG, BPF_REG_3);
> +				if (boot_cpu_has(X86_FEATURE_LFENCE_RDTSC))
> +					EMIT_LFENCE();
> +				EMIT2(0x0F, 0x31);
> +
> +				/* shl RDX, 32 */
> +				maybe_emit_1mod(&prog, BPF_REG_3, true);
> +				EMIT3(0xC1, add_1reg(0xE0, BPF_REG_3), 32);
> +				/* or RAX, RDX */
> +				maybe_emit_mod(&prog, BPF_REG_0, BPF_REG_3, true);
> +				EMIT2(0x09, add_2reg(0xC0, BPF_REG_0, BPF_REG_3));
> +				/* restore RDX from R11 */
> +				emit_mov_reg(&prog, true, BPF_REG_3, AUX_REG);
> +
> +				break;
> +			}
> +
>   			func = (u8 *) __bpf_call_base + imm32;
>   			if (tail_call_reachable) {
>   				LOAD_TAIL_CALL_CNT_PTR(bpf_prog->aux->stack_depth);
> @@ -3652,3 +3672,11 @@ u64 bpf_arch_uaddress_limit(void)
>   {
>   	return 0;
>   }
> +
> +/* x86-64 JIT can inline kfunc */
> +bool bpf_jit_inlines_kfunc_call(s32 imm)
> +{
> +	if (imm == BPF_CALL_IMM(bpf_get_cpu_cycles))
> +		return true;
> +	return false;
> +}
> diff --git a/arch/x86/net/bpf_jit_comp32.c b/arch/x86/net/bpf_jit_comp32.c
> index de0f9e5f9f73..e6097a371b69 100644
> --- a/arch/x86/net/bpf_jit_comp32.c
> +++ b/arch/x86/net/bpf_jit_comp32.c
> @@ -2094,6 +2094,13 @@ static int do_jit(struct bpf_prog *bpf_prog, int *addrs, u8 *image,
>   			if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL) {
>   				int err;
>   
> +				if (imm32 == BPF_CALL_IMM(bpf_get_cpu_cycles)) {
> +					if (boot_cpu_has(X86_FEATURE_LFENCE_RDTSC))
> +						EMIT3(0x0F, 0xAE, 0xE8);
> +					EMIT2(0x0F, 0x31);
> +					break;
> +				}
> +
>   				err = emit_kfunc_call(bpf_prog,
>   						      image + addrs[i],
>   						      insn, &prog);
> @@ -2621,3 +2628,10 @@ bool bpf_jit_supports_kfunc_call(void)
>   {
>   	return true;
>   }
> +
> +bool bpf_jit_inlines_kfunc_call(s32 imm)
> +{
> +	if (imm == BPF_CALL_IMM(bpf_get_cpu_cycles))
> +		return true;
> +	return false;
> +}

[...]

> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 395221e53832..5c6c0383ebf4 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -23,6 +23,9 @@
>   #include <linux/btf_ids.h>
>   #include <linux/bpf_mem_alloc.h>
>   #include <linux/kasan.h>
> +#if IS_ENABLED(CONFIG_GENERIC_GETTIMEOFDAY)
> +#include <vdso/datapage.h>
> +#endif
>   
>   #include "../../lib/kstrtox.h"
>   
> @@ -3023,6 +3026,13 @@ __bpf_kfunc int bpf_copy_from_user_str(void *dst, u32 dst__sz, const void __user
>   	return ret + 1;
>   }
>   
> +#if IS_ENABLED(CONFIG_GENERIC_GETTIMEOFDAY)
> +__bpf_kfunc u64 bpf_get_cpu_cycles(void)
> +{
> +	return __arch_get_hw_counter(1, NULL);

Some comment to explain what '1' mean in the above?

> +}
> +#endif
> +
>   __bpf_kfunc_end_defs();
>   
>   BTF_KFUNCS_START(generic_btf_ids)
> @@ -3115,6 +3125,9 @@ BTF_ID_FLAGS(func, bpf_get_kmem_cache)
>   BTF_ID_FLAGS(func, bpf_iter_kmem_cache_new, KF_ITER_NEW | KF_SLEEPABLE)
>   BTF_ID_FLAGS(func, bpf_iter_kmem_cache_next, KF_ITER_NEXT | KF_RET_NULL | KF_SLEEPABLE)
>   BTF_ID_FLAGS(func, bpf_iter_kmem_cache_destroy, KF_ITER_DESTROY | KF_SLEEPABLE)
> +#if IS_ENABLED(CONFIG_GENERIC_GETTIMEOFDAY)
> +BTF_ID_FLAGS(func, bpf_get_cpu_cycles, KF_FASTCALL)
> +#endif
>   BTF_KFUNCS_END(common_btf_ids)
>   
>   static const struct btf_kfunc_id_set common_kfunc_set = {
[...]