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![Jiri Olsa](/assets/img/avatar_default.png)
When unwinding the stack we need to identify each address to successfully continue. Adding latch tree to keep trampolines for quick lookup during the unwind. The patch uses first 48 bytes for latch tree node, leaving 4048 bytes from the rest of the page for trampoline or dispatcher generated code. It's still enough not to affect trampoline and dispatcher progs maximum counts. Signed-off-by: Jiri Olsa <jolsa@kernel.org> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/20200123161508.915203-3-jolsa@kernel.org
158 lines
3.6 KiB
C
158 lines
3.6 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/* Copyright(c) 2019 Intel Corporation. */
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#include <linux/hash.h>
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#include <linux/bpf.h>
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#include <linux/filter.h>
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/* The BPF dispatcher is a multiway branch code generator. The
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* dispatcher is a mechanism to avoid the performance penalty of an
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* indirect call, which is expensive when retpolines are enabled. A
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* dispatch client registers a BPF program into the dispatcher, and if
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* there is available room in the dispatcher a direct call to the BPF
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* program will be generated. All calls to the BPF programs called via
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* the dispatcher will then be a direct call, instead of an
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* indirect. The dispatcher hijacks a trampoline function it via the
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* __fentry__ of the trampoline. The trampoline function has the
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* following signature:
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*
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* unsigned int trampoline(const void *ctx, const struct bpf_insn *insnsi,
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* unsigned int (*bpf_func)(const void *,
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* const struct bpf_insn *));
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*/
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static struct bpf_dispatcher_prog *bpf_dispatcher_find_prog(
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struct bpf_dispatcher *d, struct bpf_prog *prog)
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{
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int i;
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for (i = 0; i < BPF_DISPATCHER_MAX; i++) {
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if (prog == d->progs[i].prog)
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return &d->progs[i];
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}
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return NULL;
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}
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static struct bpf_dispatcher_prog *bpf_dispatcher_find_free(
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struct bpf_dispatcher *d)
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{
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return bpf_dispatcher_find_prog(d, NULL);
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}
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static bool bpf_dispatcher_add_prog(struct bpf_dispatcher *d,
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struct bpf_prog *prog)
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{
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struct bpf_dispatcher_prog *entry;
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if (!prog)
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return false;
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entry = bpf_dispatcher_find_prog(d, prog);
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if (entry) {
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refcount_inc(&entry->users);
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return false;
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}
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entry = bpf_dispatcher_find_free(d);
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if (!entry)
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return false;
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bpf_prog_inc(prog);
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entry->prog = prog;
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refcount_set(&entry->users, 1);
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d->num_progs++;
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return true;
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}
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static bool bpf_dispatcher_remove_prog(struct bpf_dispatcher *d,
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struct bpf_prog *prog)
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{
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struct bpf_dispatcher_prog *entry;
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if (!prog)
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return false;
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entry = bpf_dispatcher_find_prog(d, prog);
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if (!entry)
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return false;
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if (refcount_dec_and_test(&entry->users)) {
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entry->prog = NULL;
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bpf_prog_put(prog);
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d->num_progs--;
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return true;
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}
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return false;
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}
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int __weak arch_prepare_bpf_dispatcher(void *image, s64 *funcs, int num_funcs)
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{
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return -ENOTSUPP;
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}
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static int bpf_dispatcher_prepare(struct bpf_dispatcher *d, void *image)
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{
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s64 ips[BPF_DISPATCHER_MAX] = {}, *ipsp = &ips[0];
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int i;
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for (i = 0; i < BPF_DISPATCHER_MAX; i++) {
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if (d->progs[i].prog)
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*ipsp++ = (s64)(uintptr_t)d->progs[i].prog->bpf_func;
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}
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return arch_prepare_bpf_dispatcher(image, &ips[0], d->num_progs);
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}
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static void bpf_dispatcher_update(struct bpf_dispatcher *d, int prev_num_progs)
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{
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void *old, *new;
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u32 noff;
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int err;
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if (!prev_num_progs) {
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old = NULL;
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noff = 0;
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} else {
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old = d->image + d->image_off;
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noff = d->image_off ^ (BPF_IMAGE_SIZE / 2);
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}
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new = d->num_progs ? d->image + noff : NULL;
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if (new) {
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if (bpf_dispatcher_prepare(d, new))
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return;
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}
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err = bpf_arch_text_poke(d->func, BPF_MOD_JUMP, old, new);
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if (err || !new)
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return;
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d->image_off = noff;
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}
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void bpf_dispatcher_change_prog(struct bpf_dispatcher *d, struct bpf_prog *from,
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struct bpf_prog *to)
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{
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bool changed = false;
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int prev_num_progs;
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if (from == to)
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return;
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mutex_lock(&d->mutex);
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if (!d->image) {
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d->image = bpf_image_alloc();
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if (!d->image)
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goto out;
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}
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prev_num_progs = d->num_progs;
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changed |= bpf_dispatcher_remove_prog(d, from);
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changed |= bpf_dispatcher_add_prog(d, to);
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if (!changed)
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goto out;
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bpf_dispatcher_update(d, prev_num_progs);
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out:
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mutex_unlock(&d->mutex);
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}
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