[bpf-next,v4,2/6] bpf: introduce BPF dispatcher

Message ID	20191211123017.13212-3-bjorn.topel@gmail.com
State	Changes Requested
Delegated to:	BPF Maintainers
Headers	show Return-Path: <bpf-owner@vger.kernel.org> From: =?utf-8?b?QmrDtnJuIFTDtnBlbA==?= <bjorn.topel@gmail.com> To: netdev@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net Cc: =?utf-8?b?QmrDtnJuIFTDtnBlbA==?= <bjorn.topel@intel.com>, bpf@vger.kernel.org, magnus.karlsson@gmail.com, magnus.karlsson@intel.com, jonathan.lemon@gmail.com, ecree@solarflare.com, thoiland@redhat.com, brouer@redhat.com, andrii.nakryiko@gmail.com Subject: [PATCH bpf-next v4 2/6] bpf: introduce BPF dispatcher Date: Wed, 11 Dec 2019 13:30:13 +0100 Message-Id: <20191211123017.13212-3-bjorn.topel@gmail.com> In-Reply-To: <20191211123017.13212-1-bjorn.topel@gmail.com> References: <20191211123017.13212-1-bjorn.topel@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: bpf-owner@vger.kernel.org Precedence: bulk
Series	Introduce the BPF dispatcher \| expand [bpf-next,v4,0/6] Introduce the BPF dispatcher [bpf-next,v4,1/6] bpf: move trampoline JIT image allocation to a function [bpf-next,v4,2/6] bpf: introduce BPF dispatcher [bpf-next,v4,3/6] bpf, xdp: start using the BPF dispatcher for XDP [bpf-next,v4,4/6] bpf: start using the BPF dispatcher in BPF_TEST_RUN [bpf-next,v4,5/6] selftests: bpf: add xdp_perf test [bpf-next,v4,6/6] bpf, x86: align dispatcher branch targets to 16B

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index b8be18427277..3ce7ad41bd6f 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -10,10 +10,12 @@ #include <linux/if_vlan.h> #include <linux/bpf.h> #include <linux/memory.h> +#include <linux/sort.h> #include <asm/extable.h> #include <asm/set_memory.h> #include <asm/nospec-branch.h> #include <asm/text-patching.h> +#include <asm/asm-prototypes.h> static u8 *emit_code(u8 *ptr, u32 bytes, unsigned int len) { @@ -1530,6 +1532,126 @@ int arch_prepare_bpf_trampoline(void *image, struct btf_func_model *m, u32 flags return 0; } +static int emit_cond_near_jump(u8 **pprog, void *func, void *ip, u8 jmp_cond) +{ + u8 *prog = *pprog; + int cnt = 0; + s64 offset; + + offset = func - (ip + 2 + 4); + if (!is_simm32(offset)) { + pr_err("Target %p is out of range\n", func); + return -EINVAL; + } + EMIT2_off32(0x0F, jmp_cond + 0x10, offset); + *pprog = prog; + return 0; +} + +static int emit_fallback_jump(u8 **pprog) +{ + u8 *prog = *pprog; + int err = 0; + +#ifdef CONFIG_RETPOLINE + /* Note that this assumes the the compiler uses external + * thunks for indirect calls. Both clang and GCC use the same + * naming convention for external thunks. + */ + err = emit_jump(&prog, __x86_indirect_thunk_rdx, prog); +#else + int cnt = 0; + + EMIT2(0xFF, 0xE2); /* jmp rdx */ +#endif + *pprog = prog; + return err; +} + +static int emit_bpf_dispatcher(u8 **pprog, int a, int b, s64 *progs) +{ + int pivot, err, jg_bytes = 1, cnt = 0; + u8 *jg_reloc, *prog = *pprog; + s64 jg_offset; + + if (a == b) { + /* Leaf node of recursion, i.e. not a range of indices + * anymore. + */ + EMIT1(add_1mod(0x48, BPF_REG_3)); /* cmp rdx,func */ + if (!is_simm32(progs[a])) + return -1; + EMIT2_off32(0x81, add_1reg(0xF8, BPF_REG_3), + progs[a]); + err = emit_cond_near_jump(&prog, /* je func */ + (void *)progs[a], prog, + X86_JE); + if (err) + return err; + + err = emit_fallback_jump(&prog); /* jmp thunk/indirect */ + if (err) + return err; + + *pprog = prog; + return 0; + } + + /* Not a leaf node, so we pivot, and recursively descend into + * the lower and upper ranges. + */ + pivot = (b - a) / 2; + EMIT1(add_1mod(0x48, BPF_REG_3)); /* cmp rdx,func */ + if (!is_simm32(progs[a + pivot])) + return -1; + EMIT2_off32(0x81, add_1reg(0xF8, BPF_REG_3), progs[a + pivot]); + + if (pivot > 2) { /* jg upper_part */ + /* Require near jump. */ + jg_bytes = 4; + EMIT2_off32(0x0F, X86_JG + 0x10, 0); + } else { + EMIT2(X86_JG, 0); + } + jg_reloc = prog; + + err = emit_bpf_dispatcher(&prog, a, a + pivot, /* emit lower_part */ + progs); + if (err) + return err; + + jg_offset = prog - jg_reloc; + emit_code(jg_reloc - jg_bytes, jg_offset, jg_bytes); + + err = emit_bpf_dispatcher(&prog, a + pivot + 1, /* emit upper_part */ + b, progs); + if (err) + return err; + + *pprog = prog; + return 0; +} + +static int cmp_ips(const void *a, const void *b) +{ + const s64 *ipa = a; + const s64 *ipb = b; + + if (*ipa > *ipb) + return 1; + if (*ipa < *ipb) + return -1; + return 0; +} + +int arch_prepare_bpf_dispatcher(void *image, s64 *funcs, int num_funcs) +{ + u8 *prog = image; + + sort(funcs, num_funcs, sizeof(funcs[0]), cmp_ips, NULL); + return emit_bpf_dispatcher(&prog, 0, num_funcs - 1, funcs); +} + struct x64_jit_data { struct bpf_binary_header *header; int *addrs; diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 5d744828b399..e6a9d74d4e30 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -470,12 +470,61 @@ struct bpf_trampoline { void *image; u64 selector; }; + +#define BPF_DISPATCHER_MAX 64 /* Fits in 2048B */ + +struct bpf_dispatcher_prog { + struct bpf_prog *prog; + refcount_t users; +}; + +struct bpf_dispatcher { + /* dispatcher mutex */ + struct mutex mutex; + void *func; + struct bpf_dispatcher_prog progs[BPF_DISPATCHER_MAX]; + int num_progs; + void *image; + u32 image_off; +}; + #ifdef CONFIG_BPF_JIT struct bpf_trampoline *bpf_trampoline_lookup(u64 key); int bpf_trampoline_link_prog(struct bpf_prog *prog); int bpf_trampoline_unlink_prog(struct bpf_prog *prog); void bpf_trampoline_put(struct bpf_trampoline *tr); void *bpf_jit_alloc_exec_page(void); +#define BPF_DISPATCHER_INIT(name) { \ + .mutex = __MUTEX_INITIALIZER(name.mutex), \ + .func = &name##func, \ + .progs = {}, \ + .num_progs = 0, \ + .image = NULL, \ + .image_off = 0 \ +} + +#define DEFINE_BPF_DISPATCHER(name) \ + unsigned int name##func( \ + const void *xdp_ctx, \ + const struct bpf_insn *insnsi, \ + unsigned int (*bpf_func)(const void *, \ + const struct bpf_insn *)) \ + { \ + return bpf_func(xdp_ctx, insnsi); \ + } \ + EXPORT_SYMBOL(name##func); \ + struct bpf_dispatcher name = BPF_DISPATCHER_INIT(name); +#define DECLARE_BPF_DISPATCHER(name) \ + unsigned int name##func( \ + const void *xdp_ctx, \ + const struct bpf_insn *insnsi, \ + unsigned int (*bpf_func)(const void *, \ + const struct bpf_insn *)); \ + extern struct bpf_dispatcher name; +#define BPF_DISPATCHER_FUNC(name) name##func +#define BPF_DISPATCHER_PTR(name) (&name) +void bpf_dispatcher_change_prog(struct bpf_dispatcher *d, struct bpf_prog *from, + struct bpf_prog *to); #else static inline struct bpf_trampoline *bpf_trampoline_lookup(u64 key) { @@ -490,6 +539,13 @@ static inline int bpf_trampoline_unlink_prog(struct bpf_prog *prog) return -ENOTSUPP; } static inline void bpf_trampoline_put(struct bpf_trampoline *tr) {} +#define DEFINE_BPF_DISPATCHER(name) +#define DECLARE_BPF_DISPATCHER(name) +#define BPF_DISPATCHER_FUNC(name) bpf_dispatcher_nopfunc +#define BPF_DISPATCHER_PTR(name) NULL +static inline void bpf_dispatcher_change_prog(struct bpf_dispatcher *d, + struct bpf_prog *from, + struct bpf_prog *to) {} #endif struct bpf_func_info_aux { diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile index 3f671bf617e8..d4f330351f87 100644 --- a/kernel/bpf/Makefile +++ b/kernel/bpf/Makefile @@ -8,6 +8,7 @@ obj-$(CONFIG_BPF_SYSCALL) += local_storage.o queue_stack_maps.o obj-$(CONFIG_BPF_SYSCALL) += disasm.o obj-$(CONFIG_BPF_JIT) += trampoline.o obj-$(CONFIG_BPF_SYSCALL) += btf.o +obj-$(CONFIG_BPF_JIT) += dispatcher.o ifeq ($(CONFIG_NET),y) obj-$(CONFIG_BPF_SYSCALL) += devmap.o obj-$(CONFIG_BPF_SYSCALL) += cpumap.o diff --git a/kernel/bpf/dispatcher.c b/kernel/bpf/dispatcher.c new file mode 100644 index 000000000000..a4690460d815 --- /dev/null +++ b/kernel/bpf/dispatcher.c @@ -0,0 +1,159 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* Copyright(c) 2019 Intel Corporation. */ + +#include <linux/hash.h> +#include <linux/bpf.h> +#include <linux/filter.h> + +/* The BPF dispatcher is a multiway branch code generator. The + * dispatcher is a mechanism to avoid the performance penalty of an + * indirect call, which is expensive when retpolines are enabled. A + * dispatch client registers a BPF program into the dispatcher, and if + * there is available room in the dispatcher a direct call to the BPF + * program will be generated. All calls to the BPF programs called via + * the dispatcher will then be a direct call, instead of an + * indirect. The dispatcher hijacks a trampoline function it via the + * __fentry__ of the trampoline. The trampoline function has the + * following signature: + * + * unsigned int trampoline(const void *xdp_ctx, + * const struct bpf_insn *insnsi, + * unsigned int (*bpf_func)(const void *, + * const struct bpf_insn *)); + */ + +static struct bpf_dispatcher_prog *bpf_dispatcher_find_prog( + struct bpf_dispatcher *d, struct bpf_prog *prog) +{ + int i; + + for (i = 0; i < BPF_DISPATCHER_MAX; i++) { + if (prog == d->progs[i].prog) + return &d->progs[i]; + } + return NULL; +} + +static struct bpf_dispatcher_prog *bpf_dispatcher_find_free( + struct bpf_dispatcher *d) +{ + return bpf_dispatcher_find_prog(d, NULL); +} + +static bool bpf_dispatcher_add_prog(struct bpf_dispatcher *d, + struct bpf_prog *prog) +{ + struct bpf_dispatcher_prog *entry; + + if (!prog) + return false; + + entry = bpf_dispatcher_find_prog(d, prog); + if (entry) { + refcount_inc(&entry->users); + return false; + } + + entry = bpf_dispatcher_find_free(d); + if (!entry) + return false; + + bpf_prog_inc(prog); + entry->prog = prog; + refcount_set(&entry->users, 1); + d->num_progs++; + return true; +} + +static bool bpf_dispatcher_remove_prog(struct bpf_dispatcher *d, + struct bpf_prog *prog) +{ + struct bpf_dispatcher_prog *entry; + + if (!prog) + return false; + + entry = bpf_dispatcher_find_prog(d, prog); + if (!entry) + return false; + + if (refcount_dec_and_test(&entry->users)) { + entry->prog = NULL; + bpf_prog_put(prog); + d->num_progs--; + return true; + } + return false; +} + +int __weak arch_prepare_bpf_dispatcher(void *image, s64 *funcs, int num_funcs) +{ + return -ENOTSUPP; +} + +static int bpf_dispatcher_prepare(struct bpf_dispatcher *d, void *image) +{ + s64 ips[BPF_DISPATCHER_MAX] = {}, *ipsp = &ips[0]; + int i; + + for (i = 0; i < BPF_DISPATCHER_MAX; i++) { + if (d->progs[i].prog) + *ipsp++ = (s64)(uintptr_t)d->progs[i].prog->bpf_func; + } + return arch_prepare_bpf_dispatcher(image, &ips[0], d->num_progs); +} + +static void bpf_dispatcher_update(struct bpf_dispatcher *d, int prev_num_progs) +{ + void *old, *new; + u32 noff; + int err; + + if (!prev_num_progs) { + old = NULL; + noff = 0; + } else { + old = d->image + d->image_off; + noff = d->image_off ^ (PAGE_SIZE / 2); + } + + new = d->num_progs ? d->image + noff : NULL; + if (new) { + if (bpf_dispatcher_prepare(d, new)) + return; + } + + err = bpf_arch_text_poke(d->func, BPF_MOD_JUMP, old, new); + if (err || !new) + return; + + d->image_off = noff; +} + +void bpf_dispatcher_change_prog(struct bpf_dispatcher *d, struct bpf_prog *from, + struct bpf_prog *to) +{ + bool changed = false; + int prev_num_progs; + + if (from == to) + return; + + mutex_lock(&d->mutex); + if (!d->image) { + d->image = bpf_jit_alloc_exec_page(); + if (!d->image) + goto out; + } + + prev_num_progs = d->num_progs; + changed |= bpf_dispatcher_remove_prog(d, from); + changed |= bpf_dispatcher_add_prog(d, to); + + if (!changed) + goto out; + + bpf_dispatcher_update(d, prev_num_progs); +out: + mutex_unlock(&d->mutex); +}

[bpf-next,v4,2/6] bpf: introduce BPF dispatcher

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