bpf: Introduce helper bpf_get_branch_snapshot

Introduce bpf_get_branch_snapshot(), which allows tracing pogram to get
branch trace from hardware (e.g. Intel LBR). To use the feature, the
user need to create perf_event with proper branch_record filtering
on each cpu, and then calls bpf_get_branch_snapshot in the bpf function.
On Intel CPUs, VLBR event (raw event 0x1b00) can be use for this.

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210910183352.3151445-3-songliubraving@fb.com

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 51cfd91..d213265 100644 (file)
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -4877,6 +4877,27 @@ union bpf_attr {
  *             Get the struct pt_regs associated with **task**.
  *     Return
  *             A pointer to struct pt_regs.
+ *
+ * long bpf_get_branch_snapshot(void *entries, u32 size, u64 flags)
+ *     Description
+ *             Get branch trace from hardware engines like Intel LBR. The
+ *             hardware engine is stopped shortly after the helper is
+ *             called. Therefore, the user need to filter branch entries
+ *             based on the actual use case. To capture branch trace
+ *             before the trigger point of the BPF program, the helper
+ *             should be called at the beginning of the BPF program.
+ *
+ *             The data is stored as struct perf_branch_entry into output
+ *             buffer *entries*. *size* is the size of *entries* in bytes.
+ *             *flags* is reserved for now and must be zero.
+ *
+ *     Return
+ *             On success, number of bytes written to *buf*. On error, a
+ *             negative value.
+ *
+ *             **-EINVAL** if *flags* is not zero.
+ *
+ *             **-ENOENT** if architecture does not support branch records.
  */
 #define __BPF_FUNC_MAPPER(FN)          \
        FN(unspec),                     \
@@ -5055,6 +5076,7 @@ union bpf_attr {
        FN(get_func_ip),                \
        FN(get_attach_cookie),          \
        FN(task_pt_regs),               \
+       FN(get_branch_snapshot),        \
        /* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper

diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index fe1e857..39eaaff 100644 (file)
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -10,6 +10,7 @@
 #include <linux/rcupdate_trace.h>
 #include <linux/rcupdate_wait.h>
 #include <linux/module.h>
+#include <linux/static_call.h>
 
 /* dummy _ops. The verifier will operate on target program's ops. */
 const struct bpf_verifier_ops bpf_extension_verifier_ops = {
@@ -526,7 +527,7 @@ out:
 }
 
 #define NO_START_TIME 1
-static u64 notrace bpf_prog_start_time(void)
+static __always_inline u64 notrace bpf_prog_start_time(void)
 {
        u64 start = NO_START_TIME;
 

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 8e2eb95..067e88c 100644 (file)
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -1017,6 +1017,34 @@ static const struct bpf_func_proto bpf_get_attach_cookie_proto_pe = {
        .arg1_type      = ARG_PTR_TO_CTX,
 };
 
+BPF_CALL_3(bpf_get_branch_snapshot, void *, buf, u32, size, u64, flags)
+{
+#ifndef CONFIG_X86
+       return -ENOENT;
+#else
+       static const u32 br_entry_size = sizeof(struct perf_branch_entry);
+       u32 entry_cnt = size / br_entry_size;
+
+       entry_cnt = static_call(perf_snapshot_branch_stack)(buf, entry_cnt);
+
+       if (unlikely(flags))
+               return -EINVAL;
+
+       if (!entry_cnt)
+               return -ENOENT;
+
+       return entry_cnt * br_entry_size;
+#endif
+}
+
+static const struct bpf_func_proto bpf_get_branch_snapshot_proto = {
+       .func           = bpf_get_branch_snapshot,
+       .gpl_only       = true,
+       .ret_type       = RET_INTEGER,
+       .arg1_type      = ARG_PTR_TO_UNINIT_MEM,
+       .arg2_type      = ARG_CONST_SIZE_OR_ZERO,
+};
+
 static const struct bpf_func_proto *
 bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 {
@@ -1132,6 +1160,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
                return &bpf_snprintf_proto;
        case BPF_FUNC_get_func_ip:
                return &bpf_get_func_ip_proto_tracing;
+       case BPF_FUNC_get_branch_snapshot:
+               return &bpf_get_branch_snapshot_proto;
        default:
                return bpf_base_func_proto(func_id);
        }

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 51cfd91..d213265 100644 (file)
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -4877,6 +4877,27 @@ union bpf_attr {
  *             Get the struct pt_regs associated with **task**.
  *     Return
  *             A pointer to struct pt_regs.
+ *
+ * long bpf_get_branch_snapshot(void *entries, u32 size, u64 flags)
+ *     Description
+ *             Get branch trace from hardware engines like Intel LBR. The
+ *             hardware engine is stopped shortly after the helper is
+ *             called. Therefore, the user need to filter branch entries
+ *             based on the actual use case. To capture branch trace
+ *             before the trigger point of the BPF program, the helper
+ *             should be called at the beginning of the BPF program.
+ *
+ *             The data is stored as struct perf_branch_entry into output
+ *             buffer *entries*. *size* is the size of *entries* in bytes.
+ *             *flags* is reserved for now and must be zero.
+ *
+ *     Return
+ *             On success, number of bytes written to *buf*. On error, a
+ *             negative value.
+ *
+ *             **-EINVAL** if *flags* is not zero.
+ *
+ *             **-ENOENT** if architecture does not support branch records.
  */
 #define __BPF_FUNC_MAPPER(FN)          \
        FN(unspec),                     \
@@ -5055,6 +5076,7 @@ union bpf_attr {
        FN(get_func_ip),                \
        FN(get_attach_cookie),          \
        FN(task_pt_regs),               \
+       FN(get_branch_snapshot),        \
        /* */
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper