Merge branch 'Reduce kmalloc / kfree churn in the verifier'

Lorenz Bauer says:

====================

github.com/cilium/ebpf runs integration tests with libbpf in a vm on CI.
I recently did some work to increase the code coverage from that, and
started experiencing OOM-kills in the VM. That led me down a rabbit
hole looking at verifier memory allocation patterns. I didn't figure out
what triggered the OOM-kills but refactored some often called memory
allocation code.

The key insight is that often times we don't need to do a full kfree /
kmalloc, but can instead just reallocate. The first patch adds two helpers
which do just that for the use cases in the verifier, which are sufficiently
different that they can't use stock krealloc_array and friends.

The series makes bpf_verif_scale about 10% faster in my VM set up, which
is especially noticeable when running with KASAN enabled.
====================
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/linux/bpf_verifier.h

@@ -215,6 +215,13 @@ struct bpf_idx_pair {
 	u32 idx;
 };
 
+struct bpf_id_pair {
+	u32 old;
+	u32 cur;
+};
+
+/* Maximum number of register states that can exist at once */
+#define BPF_ID_MAP_SIZE (MAX_BPF_REG + MAX_BPF_STACK / BPF_REG_SIZE)
 #define MAX_CALL_FRAMES 8
 struct bpf_verifier_state {
 	/* call stack tracking */
@@ -418,6 +425,7 @@ struct bpf_verifier_env {
 	const struct bpf_line_info *prev_linfo;
 	struct bpf_verifier_log log;
 	struct bpf_subprog_info subprog_info[BPF_MAX_SUBPROGS + 1];
+	struct bpf_id_pair idmap_scratch[BPF_ID_MAP_SIZE];
 	struct {
 		int *insn_state;
 		int *insn_stack;