From: Alexey Dobriyan <adobriyan@xxxxxxxxx> Subject: fs/binfmt_elf.c: better codegen around current->mm "current->mm" pointer is stable in general except few cases one of which execve(2). Compiler can't treat is as stable but it _is_ stable most of the time. During ELF loading process ->mm becomes stable right after flush_old_exec(). Help compiler by caching current->mm, otherwise it continues to refetch it. add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-141 (-141) Function old new delta elf_core_dump 5062 5039 -23 load_elf_binary 5426 5308 -118 Note: other cases are left as is because it is either pessimisation or no change in binary size. Link: http://lkml.kernel.org/r/20191215124755.GB21124@avx2 Signed-off-by: Alexey Dobriyan <adobriyan@xxxxxxxxx> Reviewed-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/binfmt_elf.c | 52 ++++++++++++++++++++++++---------------------- 1 file changed, 28 insertions(+), 24 deletions(-) --- a/fs/binfmt_elf.c~elf-better-codegen-around-current-mm +++ a/fs/binfmt_elf.c @@ -165,6 +165,7 @@ create_elf_tables(struct linux_binprm *b unsigned long load_addr, unsigned long interp_load_addr, unsigned long e_entry) { + struct mm_struct *mm = current->mm; unsigned long p = bprm->p; int argc = bprm->argc; int envc = bprm->envc; @@ -227,7 +228,7 @@ create_elf_tables(struct linux_binprm *b return -EFAULT; /* Create the ELF interpreter info */ - elf_info = (elf_addr_t *)current->mm->saved_auxv; + elf_info = (elf_addr_t *)mm->saved_auxv; /* update AT_VECTOR_SIZE_BASE if the number of NEW_AUX_ENT() changes */ #define NEW_AUX_ENT(id, val) \ do { \ @@ -276,13 +277,13 @@ create_elf_tables(struct linux_binprm *b } #undef NEW_AUX_ENT /* AT_NULL is zero; clear the rest too */ - memset(elf_info, 0, (char *)current->mm->saved_auxv + - sizeof(current->mm->saved_auxv) - (char *)elf_info); + memset(elf_info, 0, (char *)mm->saved_auxv + + sizeof(mm->saved_auxv) - (char *)elf_info); /* And advance past the AT_NULL entry. */ elf_info += 2; - ei_index = elf_info - (elf_addr_t *)current->mm->saved_auxv; + ei_index = elf_info - (elf_addr_t *)mm->saved_auxv; sp = STACK_ADD(p, ei_index); items = (argc + 1) + (envc + 1) + 1; @@ -301,7 +302,7 @@ create_elf_tables(struct linux_binprm *b * Grow the stack manually; some architectures have a limit on how * far ahead a user-space access may be in order to grow the stack. */ - vma = find_extend_vma(current->mm, bprm->p); + vma = find_extend_vma(mm, bprm->p); if (!vma) return -EFAULT; @@ -310,7 +311,7 @@ create_elf_tables(struct linux_binprm *b return -EFAULT; /* Populate list of argv pointers back to argv strings. */ - p = current->mm->arg_end = current->mm->arg_start; + p = mm->arg_end = mm->arg_start; while (argc-- > 0) { size_t len; if (__put_user((elf_addr_t)p, sp++)) @@ -322,10 +323,10 @@ create_elf_tables(struct linux_binprm *b } if (__put_user(0, sp++)) return -EFAULT; - current->mm->arg_end = p; + mm->arg_end = p; /* Populate list of envp pointers back to envp strings. */ - current->mm->env_end = current->mm->env_start = p; + mm->env_end = mm->env_start = p; while (envc-- > 0) { size_t len; if (__put_user((elf_addr_t)p, sp++)) @@ -337,10 +338,10 @@ create_elf_tables(struct linux_binprm *b } if (__put_user(0, sp++)) return -EFAULT; - current->mm->env_end = p; + mm->env_end = p; /* Put the elf_info on the stack in the right place. */ - if (copy_to_user(sp, current->mm->saved_auxv, ei_index * sizeof(elf_addr_t))) + if (copy_to_user(sp, mm->saved_auxv, ei_index * sizeof(elf_addr_t))) return -EFAULT; return 0; } @@ -701,6 +702,7 @@ static int load_elf_binary(struct linux_ struct elfhdr interp_elf_ex; } *loc; struct arch_elf_state arch_state = INIT_ARCH_ELF_STATE; + struct mm_struct *mm; struct pt_regs *regs; loc = kmalloc(sizeof(*loc), GFP_KERNEL); @@ -1096,11 +1098,13 @@ out_free_interp: load_addr, interp_load_addr, e_entry); if (retval < 0) goto out; - current->mm->end_code = end_code; - current->mm->start_code = start_code; - current->mm->start_data = start_data; - current->mm->end_data = end_data; - current->mm->start_stack = bprm->p; + + mm = current->mm; + mm->end_code = end_code; + mm->start_code = start_code; + mm->start_data = start_data; + mm->end_data = end_data; + mm->start_stack = bprm->p; if ((current->flags & PF_RANDOMIZE) && (randomize_va_space > 1)) { /* @@ -1111,12 +1115,11 @@ out_free_interp: * growing down), and into the unused ELF_ET_DYN_BASE region. */ if (IS_ENABLED(CONFIG_ARCH_HAS_ELF_RANDOMIZE) && - elf_ex->e_type == ET_DYN && !interpreter) - current->mm->brk = current->mm->start_brk = - ELF_ET_DYN_BASE; + elf_ex->e_type == ET_DYN && !interpreter) { + mm->brk = mm->start_brk = ELF_ET_DYN_BASE; + } - current->mm->brk = current->mm->start_brk = - arch_randomize_brk(current->mm); + mm->brk = mm->start_brk = arch_randomize_brk(mm); #ifdef compat_brk_randomized current->brk_randomized = 1; #endif @@ -1574,6 +1577,7 @@ static void fill_siginfo_note(struct mem */ static int fill_files_note(struct memelfnote *note) { + struct mm_struct *mm = current->mm; struct vm_area_struct *vma; unsigned count, size, names_ofs, remaining, n; user_long_t *data; @@ -1581,7 +1585,7 @@ static int fill_files_note(struct memelf char *name_base, *name_curpos; /* *Estimated* file count and total data size needed */ - count = current->mm->map_count; + count = mm->map_count; if (count > UINT_MAX / 64) return -EINVAL; size = count * 64; @@ -1599,7 +1603,7 @@ static int fill_files_note(struct memelf name_base = name_curpos = ((char *)data) + names_ofs; remaining = size - names_ofs; count = 0; - for (vma = current->mm->mmap; vma != NULL; vma = vma->vm_next) { + for (vma = mm->mmap; vma != NULL; vma = vma->vm_next) { struct file *file; const char *filename; @@ -1633,10 +1637,10 @@ static int fill_files_note(struct memelf data[0] = count; data[1] = PAGE_SIZE; /* - * Count usually is less than current->mm->map_count, + * Count usually is less than mm->map_count, * we need to move filenames down. */ - n = current->mm->map_count - count; + n = mm->map_count - count; if (n != 0) { unsigned shift_bytes = n * 3 * sizeof(data[0]); memmove(name_base - shift_bytes, name_base, _
