From 29fcf9ce4bbdf4cc339def776860e1c0095bca98 Mon Sep 17 00:00:00 2001 From: Jiri Olsa Date: Thu, 10 Sep 2026 11:43:53 +0200 Subject: [PATCH] bpf, x86: Use global buffer for trampoline size generation Currently arch_bpf_trampoline_size allocates and frees a temporary trampoline buffer on every invocation. The buffer is only used as a scratch space while __arch_prepare_bpf_trampoline() calculates the required size, and the generated trampoline is discarded. Allocating a writable scratch page during kernel initialization and reusing it for all size calculations. This improves tracing_multi attachment time. With current code: # ./test_progs -t tracing_multi_bench_attach -v ... serial_test_tracing_multi_bench_attach: found 55227 functions serial_test_tracing_multi_bench_attach: attached in 1.563s serial_test_tracing_multi_bench_attach: detached in 0.256s With the fix: # ./test_progs -t tracing_multi_bench_attach -v ... serial_test_tracing_multi_bench_attach: found 55235 functions serial_test_tracing_multi_bench_attach: attached in 0.798s serial_test_tracing_multi_bench_attach: detached in 0.258s Signed-off-by: Jiri Olsa Link: https://lore.kernel.org/r/20260910094353.1256316-1-jolsa@kernel.org Signed-off-by: Alexei Starovoitov --- arch/x86/net/bpf_jit_comp.c | 36 +++++++++++++++++++++--------------- 1 file changed, 21 insertions(+), 15 deletions(-) diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 2671e4118d00..d4a980140b48 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -9,6 +9,7 @@ #include #include #include +#include #include #include #include @@ -35,6 +36,21 @@ void __asan_store8(void *p); static bool all_callee_regs_used[4] = {true, true, true, true}; +static void *trampoline_size_image; + +static int __init init_trampoline_size_image(void) +{ + /* + * The generated trampoline contains calls and jumps with 32bit relative + * offsets, so the scratch image must be in the execmem range. + * On x86, module data and executable memory share the same address range, + * so using EXECMEM_MODULE_DATA to get writable memory. + */ + trampoline_size_image = execmem_alloc(EXECMEM_MODULE_DATA, PAGE_SIZE); + return trampoline_size_image ? 0 : -ENOMEM; +} +late_initcall(init_trampoline_size_image); + static u8 *emit_code(u8 *ptr, u32 bytes, unsigned int len) { if (len == 1) @@ -4067,24 +4083,14 @@ int arch_bpf_trampoline_size(const struct btf_func_model *m, u32 flags, struct bpf_tramp_nodes *tnodes, void *func_addr) { struct bpf_tramp_image im; - void *image; - int ret; - /* Allocate a temporary buffer for __arch_prepare_bpf_trampoline(). - * - * We cannot use kvmalloc here, because we need image to be in - * module memory range. - * Since it must be writable use execmem_alloc(EXECMEM_MODULE_DATA) - * that returns writable memory in the module address space. - */ - image = execmem_alloc(EXECMEM_MODULE_DATA, PAGE_SIZE); - if (!image) + if (!trampoline_size_image) return -ENOMEM; - ret = __arch_prepare_bpf_trampoline(&im, image, image + PAGE_SIZE, image, - m, flags, tnodes, func_addr); - execmem_free(image); - return ret; + return __arch_prepare_bpf_trampoline(&im, trampoline_size_image, + trampoline_size_image + PAGE_SIZE, + trampoline_size_image, m, flags, + tnodes, func_addr); } static int emit_bpf_dispatcher(u8 **pprog, int a, int b, s64 *progs, u8 *image, u8 *buf)