On Wed, 18 May 2016 02:09:37 +0530
Anju T <a...@linux.vnet.ibm.com> wrote:
> Instruction slot for detour buffer is allocated from
> the reserved area. For the time being 64KB is reserved
> in memory for this purpose. ppc_get_optinsn_slot() and
> ppc_free_optinsn_slot() are geared towards the allocation and freeing
> of memory from this area.
Thank you for porting optprobe on ppc!!
I have some comments on this patch.
>
> Signed-off-by: Anju T <a...@linux.vnet.ibm.com>
> ---
> arch/powerpc/kernel/optprobes.c | 463
> ++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 463 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..50a60c1
> --- /dev/null
> +++ b/arch/powerpc/kernel/optprobes.c
> @@ -0,0 +1,463 @@
> +/*
> + * 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>
> +
> +/* Reserve an area to allocate slots for detour buffer */
> +extern void optprobe_trampoline_holder(void)
> +{
> + asm volatile(".global optinsn_slot\n"
> + "optinsn_slot:\n"
> + ".space 65536");
> +}
Would we better move this into optprobes_head.S?
> +
> +#define SLOT_SIZE 65536
> +#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_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)
> +
> +struct kprobe_ppc_insn_page {
> + struct list_head list;
> + kprobe_opcode_t *insns; /* Page of instruction slots */
> + struct kprobe_insn_cache *cache;
> + int nused;
> + int ngarbage;
> + char slot_used[];
> +};
> +
> +#define PPC_KPROBE_INSN_PAGE_SIZE(slots) \
> + (offsetof(struct kprobe_ppc_insn_page, slot_used) + \
> + (sizeof(char) * (slots)))
> +
> +enum ppc_kprobe_slot_state {
> + SLOT_CLEAN = 0,
> + SLOT_DIRTY = 1,
> + SLOT_USED = 2,
> +};
> +
> +static 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 is initialized later */
> + .nr_garbage = 0,
> +};
> +
> +static int ppc_slots_per_page(struct kprobe_insn_cache *c)
> +{
> + /*
> + * Here the #slots per page differs from x86 as we have
> + * only 64KB reserved.
> + */
> + return SLOT_SIZE / (c->insn_size * sizeof(kprobe_opcode_t));
> +}
> +
> +/* Return 1 if all garbages are collected, otherwise 0. */
> +static int collect_one_slot(struct kprobe_ppc_insn_page *kip, int idx)
> +{
> + kip->slot_used[idx] = SLOT_CLEAN;
> + kip->nused--;
> + return 0;
> +}
> +
> +static int collect_garbage_slots(struct kprobe_insn_cache *c)
> +{
> + struct kprobe_ppc_insn_page *kip, *next;
> +
> + /* Ensure no-one is interrupted on the garbages */
> + synchronize_sched();
> +
> + list_for_each_entry_safe(kip, next, &c->pages, list) {
> + int i;
> +
> + if (kip->ngarbage == 0)
> + continue;
> + kip->ngarbage = 0; /* we will collect all garbages */
> + for (i = 0; i < ppc_slots_per_page(c); i++) {
> + if (kip->slot_used[i] == SLOT_DIRTY &&
> + collect_one_slot(kip, i))
> + break;
> + }
> + }
> + c->nr_garbage = 0;
> + return 0;
> +}
> +
> +kprobe_opcode_t *__ppc_get_optinsn_slot(struct kprobe_insn_cache *c)
> +{
> + struct kprobe_ppc_insn_page *kip;
> + kprobe_opcode_t *slot = NULL;
> +
> + mutex_lock(&c->mutex);
> + list_for_each_entry(kip, &c->pages, list) {
> + if (kip->nused < ppc_slots_per_page(c)) {
> + int i;
> +
> + for (i = 0; i < ppc_slots_per_page(c); i++) {
> + if (kip->slot_used[i] == SLOT_CLEAN) {
> + kip->slot_used[i] = SLOT_USED;
> + kip->nused++;
> + slot = kip->insns + (i * c->insn_size);
> + goto out;
> + }
> + }
> + /* kip->nused reached max value. */
> + kip->nused = ppc_slots_per_page(c);
> + pr_info("No more slots to allocate\n");
> + WARN_ON(1);
> + goto out;
> + }
> + }
Wait... this should have just one or zero kip on the list.
And if !list_empty(c->pages) here, we have to return NULL.
> + kip = kmalloc(PPC_KPROBE_INSN_PAGE_SIZE(ppc_slots_per_page(c)),
> + GFP_KERNEL);
> + if (!kip)
> + goto out;
> + /*
> + * Allocate from the reserved area so as to
> + * ensure the range will be within +/-32MB
> + */
> + kip->insns = &optinsn_slot;
> + if (!kip->insns) {
> + kfree(kip);
> + goto out;
> + }
> + INIT_LIST_HEAD(&kip->list);
> + memset(kip->slot_used, SLOT_CLEAN, ppc_slots_per_page(c));
> + kip->slot_used[0] = SLOT_USED;
> + kip->nused = 1;
> + kip->ngarbage = 0;
> + kip->cache = c;
> + list_add(&kip->list, &c->pages);
> + slot = kip->insns;
> +out:
> + mutex_unlock(&c->mutex);
> + return slot;
> +}
> +
> +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 = __ppc_get_optinsn_slot(&kprobe_ppc_optinsn_slots);
> + else
> + pr_info("Kprobe can not be optimized\n");
> + return slot;
> +}
> +NOKPROBE_SYMBOL(ppc_get_optinsn_slot);
You don't need it, unless this is called in kprobe handler.
> +
> +void __ppc_free_optinsn_slot(struct kprobe_insn_cache *c,
> + kprobe_opcode_t *slot, int dirty)
> +{
> + struct kprobe_ppc_insn_page *kip;
> +
> + mutex_lock(&c->mutex);
> +
> + list_for_each_entry(kip, &c->pages, list) {
> + long idx = ((long)slot - (long)kip->insns) /
> + (c->insn_size * sizeof(kprobe_opcode_t));
> + if (idx >= 0 && idx < ppc_slots_per_page(c)) {
> + WARN_ON(kip->slot_used[idx] != SLOT_USED);
> + if (dirty) {
> + kip->slot_used[idx] = SLOT_DIRTY;
> + kip->ngarbage++;
> + if (++c->nr_garbage > ppc_slots_per_page(c))
> + collect_garbage_slots(c);
> + } else
> + collect_one_slot(kip, idx);
> + goto out;
> + }
> + }
> + /* Could not free this slot. */
> + WARN_ON(1);
> +out:
> + mutex_unlock(&c->mutex);
> +}
> +
> +static void ppc_free_optinsn_slot(struct optimized_kprobe *op)
> +{
> + if (!op->optinsn.insn)
> + return;
> + if (is_kernel_addr((unsigned long)op->kp.addr))
> + __ppc_free_optinsn_slot(&kprobe_ppc_optinsn_slots,
> + op->optinsn.insn, 0);
> +}
> +NOKPROBE_SYMBOL(ppc_free_optinsn_slot);
ditto.
> +
> +static void
> +__arch_remove_optimized_kprobe(struct optimized_kprobe *op, int dirty)
> +{
> + if (op->optinsn.insn) {
> + ppc_free_optinsn_slot(op);
> + op->optinsn.insn = NULL;
> + }
> +}
> +
> +static int can_optimize(struct kprobe *p)
> +{
> + /*
> + * Not optimizing the kprobe placed by
> + * kretprobe during boot time
> + */
> + struct pt_regs *regs;
> + unsigned int instr;
> + int r;
> +
> + if ((kprobe_opcode_t)p->addr == (kprobe_opcode_t)&kretprobe_trampoline)
> + return 0;
> +
> + regs = current_pt_regs();
> + instr = *(p->ainsn.insn);
> +
> + /* Ensure the instruction can be emulated*/
> + r = emulate_step(regs, instr);
> + 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;
> +
> + branch = create_branch((unsigned int *)buff + TMPL_RET_IDX,
> + (unsigned long)ret, 0);
> + buff[TMPL_RET_IDX] = branch;
> +}
> +NOKPROBE_SYMBOL(create_return_branch);
ditto.
> +
> +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);
> +}
This actually needs to be marked NOKPROBE_SYMBOL().
> +
> +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)
> +{
> + unsigned int instr, instr2;
> +
> + instr = 0x3c000000 | 0x800000 | ((insn >> 16) & 0xffff);
> + *addr++ = instr;
> + instr2 = 0x60000000 | 0x40000 | 0x800000;
> + instr2 = instr2 | (insn & 0xffff);
> + *addr = instr2;
Please add macros and/or comments for each instruction to explain what
instrcution would you make...
> +}
> +
> +void create_load_address_insn(struct optimized_kprobe *op,
> + kprobe_opcode_t *addr, kprobe_opcode_t *addr2)
> +{
> + unsigned int instr1, instr2, instr3, instr4, instr5;
Would it better use u32?
> + unsigned long val;
> +
> + val = op;
> +
> + instr1 = 0x3c000000 | 0x600000 | ((val >> 48) & 0xffff);
> + *addr++ = instr1;
> + *addr2++ = instr1;
> + instr2 = 0x60000000 | 0x30000 | 0x600000 | ((val >> 32) & 0xffff);
> + *addr++ = instr2;
> + *addr2++ = instr2;
> + instr3 = 0x78000004 | 0x30000 | 0x600000 | ((32 & 0x1f) << 11);
> + instr3 = instr3 | ((31 & 0x1f) << 6) | ((32 & 0x20) >> 4);
> + *addr++ = instr3;
> + *addr2++ = instr3;
> + instr4 = 0x64000000 | 0x30000 | 0x600000 | ((val >> 16) & 0xffff);
> + *addr++ = instr4;
> + *addr2++ = instr4;
> + instr5 = 0x60000000 | 0x30000 | 0x600000 | (val & 0xffff);
Ditto.
> + *addr = instr5;
> + *addr2 = 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);
> +
> + /*
> + * 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;
Why would you add a new line?
> + if (rel_chk < -0x2000000 || rel_chk > 0x1fffffc || rel_chk & 0x3) {
> + ppc_free_optinsn_slot(op);
> + return -ERANGE;
> + }
> + /*
> + * For the time being assume that the return address is NIP+4.
> + * TODO : check the return address is also within 32MB range for
> + * cases where NIP is not NIP+4.ie the NIP is decided after emulation.
> + */
> + ret_chk = (long)(buff + TMPL_RET_IDX) - (unsigned long)(p->addr) + 4;
> +
> + 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(op, buff + TMPL_OP1_IDX, 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;
> + 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);
Please add indent-tab for this block.
> + }
> +}
> +
> +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)
> +{
Please make sure addr != op->kp.addr and addr is aligned.
> + return 0;
> +}
> --
> 2.1.0
>
Thanks!
--
Masami Hiramatsu <mhira...@kernel.org>
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