[RFC PATCH v3 2/3] arch/powerpc : optprobes for powerpc core
Masami Hiramatsu
mhiramat at kernel.org
Wed Jun 1 00:55:38 AEST 2016
On Tue, 31 May 2016 16:26:30 +0530
Anju T <anju at linux.vnet.ibm.com> wrote:
> Instructions which can be emulated are suppliants for
> optimization. Before optimization ensure that the address range
> between the detour buffer allocated and the instruction being probed
> is within +/- 32MB.
>
> Signed-off-by: Anju T <anju at linux.vnet.ibm.com>
> ---
> arch/powerpc/kernel/optprobes.c | 351 ++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 351 insertions(+)
> create mode 100644 arch/powerpc/kernel/optprobes.c
>
> diff --git a/arch/powerpc/kernel/optprobes.c b/arch/powerpc/kernel/optprobes.c
> new file mode 100644
> index 0000000..c4253b6
> --- /dev/null
> +++ b/arch/powerpc/kernel/optprobes.c
> @@ -0,0 +1,351 @@
> +/*
> + * Code for Kernel probes Jump optimization.
> + *
> + * Copyright 2016, Anju T, IBM Corp.
> + *
> + * This program is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU General Public License
> + * as published by the Free Software Foundation; either version
> + * 2 of the License, or (at your option) any later version.
> + */
> +
> +#include <linux/kprobes.h>
> +#include <linux/jump_label.h>
> +#include <linux/types.h>
> +#include <linux/slab.h>
> +#include <linux/list.h>
> +#include <asm/kprobes.h>
> +#include <asm/ptrace.h>
> +#include <asm/cacheflush.h>
> +#include <asm/code-patching.h>
> +#include <asm/sstep.h>
> +
> +DEFINE_INSN_CACHE_OPS(ppc_optinsn)
> +
> +#define TMPL_CALL_HDLR_IDX \
> + (optprobe_template_call_handler - optprobe_template_entry)
> +#define TMPL_EMULATE_IDX \
> + (optprobe_template_call_emulate - optprobe_template_entry)
> +#define TMPL_RET_BRANCH_IDX \
> + (optprobe_template_ret_branch - optprobe_template_entry)
> +#define TMPL_RET_IDX \
> + (optprobe_template_ret - optprobe_template_entry)
> +#define TMPL_KP_IDX \
> + (optprobe_template_kp_addr - optprobe_template_entry)
> +#define TMPL_OP1_IDX \
> + (optprobe_template_op_address1 - optprobe_template_entry)
> +#define TMPL_OP2_IDX \
> + (optprobe_template_op_address2 - optprobe_template_entry)
> +#define TMPL_INSN_IDX \
> + (optprobe_template_insn - optprobe_template_entry)
> +#define TMPL_END_IDX \
> + (optprobe_template_end - optprobe_template_entry)
> +
> +static unsigned long val_nip;
> +
> +static void *__ppc_alloc_insn_page(void)
> +{
> + return &optinsn_slot;
> +}
> +
> +static void *__ppc_free_insn_page(void *page __maybe_unused)
> +{
> + return;
> +}
Hmm, you should not return optinsn_slot twice or more, because
it actually doesn't allocate memory but just returns reserved
memory area. So, it should be something like this;
static bool insn_page_in_use;
static void *__ppc_alloc_insn_page(void)
{
if (insn_page_in_use)
return NULL;
insn_page_in_use = true;
return &optinsn_slot;
}
static void *__ppc_free_insn_page(void *page __maybe_unused)
{
insn_page_in_use = false;
}
> +
> +struct kprobe_insn_cache kprobe_ppc_optinsn_slots = {
> + .mutex = __MUTEX_INITIALIZER(kprobe_ppc_optinsn_slots.mutex),
> + .pages = LIST_HEAD_INIT(kprobe_ppc_optinsn_slots.pages),
> + /* insn_size initialized later */
> + .alloc = __ppc_alloc_insn_page,
> + .free = __ppc_free_insn_page,
> + .nr_garbage = 0,
> +};
> +
> +kprobe_opcode_t *ppc_get_optinsn_slot(struct optimized_kprobe *op)
> +{
> + /*
> + * The insn slot is allocated from the reserved
> + * area(ie &optinsn_slot).We are not optimizing probes
> + * at module_addr now.
> + */
> + kprobe_opcode_t *slot = NULL;
> +
> + if (is_kernel_addr(op->kp.addr))
> + slot = get_ppc_optinsn_slot();
> + return slot;
> +}
> +
> +static void ppc_free_optinsn_slot(struct optimized_kprobe *op)
> +{
> + if (!op->optinsn.insn)
> + return;
> + if (is_kernel_addr((unsigned long)op->kp.addr))
> + free_ppc_optinsn_slot(op->optinsn.insn, 0);
> +}
> +
> +static void
> +__arch_remove_optimized_kprobe(struct optimized_kprobe *op, int dirty)
> +{
> + ppc_free_optinsn_slot(op);
> + op->optinsn.insn = NULL;
> +}
> +
> +static int can_optimize(struct kprobe *p)
> +{
> + struct pt_regs *regs;
> + unsigned int instr;
> + int r;
> +
> + /*
> + * Not optimizing the kprobe placed by
> + * kretprobe during boot time
> + */
> + if ((kprobe_opcode_t)p->addr == (kprobe_opcode_t)&kretprobe_trampoline)
> + return 0;
> +
> + regs = kmalloc(sizeof(*regs), GFP_KERNEL);
> + if (!regs)
> + return -ENOMEM;
> + memset(regs, 0, sizeof(struct pt_regs));
> + memcpy(regs, current_pt_regs(), sizeof(struct pt_regs));
> + regs->nip = p->addr;
> + instr = *(p->ainsn.insn);
> +
> + /* Ensure the instruction can be emulated*/
> + r = emulate_step(regs, instr);
> + val_nip = regs->nip;
> + if (r != 1)
> + return 0;
> +
> + return 1;
> +}
> +
> +static void
> +create_return_branch(struct optimized_kprobe *op, struct pt_regs *regs)
> +{
> + /*
> + * Create a branch back to the return address
> + * after the probed instruction is emulated
> + */
> +
> + kprobe_opcode_t branch, *buff;
> + unsigned long ret;
> +
> + ret = regs->nip;
> + buff = op->optinsn.insn;
> + /*
> + * TODO: For conditional branch instructions, the return
> + * address may differ in SMP systems.This has to be addressed.
> + */
> +
> + branch = create_branch((unsigned int *)buff + TMPL_RET_IDX,
> + (unsigned long)ret, 0);
> + buff[TMPL_RET_IDX] = branch;
> + isync();
> +}
> +
> +static void
> +optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
> +{
> + struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> + unsigned long flags;
> +
> + local_irq_save(flags);
> +
> + if (kprobe_running())
> + kprobes_inc_nmissed_count(&op->kp);
> + else {
> + __this_cpu_write(current_kprobe, &op->kp);
> + kcb->kprobe_status = KPROBE_HIT_ACTIVE;
> + opt_pre_handler(&op->kp, regs);
> + __this_cpu_write(current_kprobe, NULL);
> + }
> + local_irq_restore(flags);
> +}
> +NOKPROBE_SYMBOL(optimized_callback);
> +
> +void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
> +{
> + __arch_remove_optimized_kprobe(op, 1);
> +}
> +
> +void create_insn(unsigned int insn, kprobe_opcode_t *addr)
> +{
> + u32 instr, instr2;
> +
> + /*
> + * emulate_step() requires insn to be emulated as
> + * second parameter. Hence r4 should be loaded
> + * with 'insn'.
> + * synthesize addis r4,0,(insn)@h
> + */
> + instr = 0x3c000000 | 0x800000 | ((insn >> 16) & 0xffff);
> + *addr++ = instr;
> +
> + /* ori r4,r4,(insn)@l */
> + instr2 = 0x60000000 | 0x40000 | 0x800000;
> + instr2 = instr2 | (insn & 0xffff);
> + *addr = instr2;
> +}
> +
> +void create_load_address_insn(unsigned long val, kprobe_opcode_t *addr)
> +{
> + u32 instr1, instr2, instr3, instr4, instr5;
> + /*
> + * Optimized_kprobe structure is required as a parameter
> + * for invoking optimized_callback() and create_return_branch()
> + * from detour buffer. Hence need to have a 64bit immediate
> + * load into r3.
> + *
> + * lis r3,(op)@highest
> + */
> + instr1 = 0x3c000000 | 0x600000 | ((val >> 48) & 0xffff);
> + *addr++ = instr1;
> +
> + /* ori r3,r3,(op)@higher */
> + instr2 = 0x60000000 | 0x30000 | 0x600000 | ((val >> 32) & 0xffff);
> + *addr++ = instr2;
> +
> + /* rldicr r3,r3,32,31 */
> + instr3 = 0x78000004 | 0x30000 | 0x600000 | ((32 & 0x1f) << 11);
> + instr3 = instr3 | ((31 & 0x1f) << 6) | ((32 & 0x20) >> 4);
> + *addr++ = instr3;
> +
> + /* oris r3,r3,(op)@h */
> + instr4 = 0x64000000 | 0x30000 | 0x600000 | ((val >> 16) & 0xffff);
> + *addr++ = instr4;
> +
> + /* ori r3,r3,(op)@l */
> + instr5 = 0x60000000 | 0x30000 | 0x600000 | (val & 0xffff);
> + *addr = instr5;
> +}
> +
> +int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
> +{
> + kprobe_opcode_t *buff, branch, branch2, branch3;
> + long rel_chk, ret_chk;
> +
> + kprobe_ppc_optinsn_slots.insn_size = MAX_OPTINSN_SIZE;
> + op->optinsn.insn = NULL;
> +
> + if (!can_optimize(p))
> + return -EILSEQ;
> +
> + /* Allocate instruction slot for detour buffer*/
> + buff = ppc_get_optinsn_slot(op);
> + if (!buff)
> + return -ENOMEM;
> +
> + /*
> + * OPTPROBE use a 'b' instruction to branch to optinsn.insn.
> + *
> + * The target address has to be relatively nearby, to permit use
> + * of branch instruction in powerpc because the address is specified
> + * in an immediate field in the instruction opcode itself, ie 24 bits
> + * in the opcode specify the address. Therefore the address gap should
> + * be 32MB on either side of the current instruction.
> + */
> + rel_chk = (long)buff - (unsigned long)p->addr;
> + if (rel_chk < -0x2000000 || rel_chk > 0x1fffffc || rel_chk & 0x3) {
> + ppc_free_optinsn_slot(op);
> + return -ERANGE;
> + }
> + /* Check the return address is also within 32MB range */
> + ret_chk = (long)(buff + TMPL_RET_IDX) - (unsigned long)val_nip;
No, please don't pass the "regs->nip" via hidden channel like as this val_nip
static local variable. Instead, you should run emulate_step() again here,
or, at least you must keep the address and compare it. I recommend former.
Thank you,
> + if (ret_chk < -0x2000000 || ret_chk > 0x1fffffc || ret_chk & 0x3) {
> + ppc_free_optinsn_slot(op);
> + return -ERANGE;
> + }
> +
> + /* Do Copy arch specific instance from template*/
> + memcpy(buff, optprobe_template_entry,
> + TMPL_END_IDX * sizeof(kprobe_opcode_t));
> + create_load_address_insn((unsigned long)p->addr, buff + TMPL_KP_IDX);
> + create_load_address_insn((unsigned long)op, buff + TMPL_OP1_IDX);
> + create_load_address_insn((unsigned long)op, buff + TMPL_OP2_IDX);
> +
> + /* Create a branch to the optimized_callback function */
> + branch = create_branch((unsigned int *)buff + TMPL_CALL_HDLR_IDX,
> + (unsigned long)optimized_callback + 8,
> + BRANCH_SET_LINK);
> +
> + /* Place the branch instr into the trampoline */
> + buff[TMPL_CALL_HDLR_IDX] = branch;
> + create_insn(*(p->ainsn.insn), buff + TMPL_INSN_IDX);
> +
> + /*Create a branch instruction into the emulate_step*/
> + branch3 = create_branch((unsigned int *)buff + TMPL_EMULATE_IDX,
> + (unsigned long)emulate_step + 8,
> + BRANCH_SET_LINK);
> + buff[TMPL_EMULATE_IDX] = branch3;
> +
> + /* Create a branch for jumping back*/
> + branch2 = create_branch((unsigned int *)buff + TMPL_RET_BRANCH_IDX,
> + (unsigned long)create_return_branch + 8,
> + BRANCH_SET_LINK);
> + buff[TMPL_RET_BRANCH_IDX] = branch2;
> +
> + op->optinsn.insn = buff;
> + smp_mb();
> + return 0;
> +}
> +
> +int arch_prepared_optinsn(struct arch_optimized_insn *optinsn)
> +{
> + return optinsn->insn;
> +}
> +
> +/*
> + * Here,kprobe opt always replace one instruction (4 bytes
> + * aligned and 4 bytes long). It is impossible to encounter another
> + * kprobe in the address range. So always return 0.
> + */
> +int arch_check_optimized_kprobe(struct optimized_kprobe *op)
> +{
> + return 0;
> +}
> +
> +void arch_optimize_kprobes(struct list_head *oplist)
> +{
> + struct optimized_kprobe *op;
> + struct optimized_kprobe *tmp;
> +
> + unsigned int branch;
> +
> + list_for_each_entry_safe(op, tmp, oplist, list) {
> + /*
> + * Backup instructions which will be replaced
> + *by jump address
> + */
> + memcpy(op->optinsn.copied_insn, op->kp.addr,
> + RELATIVEJUMP_SIZE);
> + branch = create_branch((unsigned int *)op->kp.addr,
> + (unsigned long)op->optinsn.insn, 0);
> + *op->kp.addr = branch;
> + list_del_init(&op->list);
> + }
> +}
> +
> +void arch_unoptimize_kprobe(struct optimized_kprobe *op)
> +{
> + arch_arm_kprobe(&op->kp);
> +}
> +
> +void arch_unoptimize_kprobes(struct list_head *oplist,
> + struct list_head *done_list)
> +{
> + struct optimized_kprobe *op;
> + struct optimized_kprobe *tmp;
> +
> + list_for_each_entry_safe(op, tmp, oplist, list) {
> + arch_unoptimize_kprobe(op);
> + list_move(&op->list, done_list);
> + }
> +}
> +
> +int arch_within_optimized_kprobe(struct optimized_kprobe *op,
> + unsigned long addr)
> +{
> + return 0;
> +}
> --
> 2.1.0
>
--
Masami Hiramatsu <mhiramat at kernel.org>
More information about the Linuxppc-dev
mailing list