Messages in this thread | | | Date | Thu, 19 May 2016 00:13:04 +0900 | From | Masami Hiramatsu <> | Subject | Re: [RFC PATCH 2/3] arch/powerpc : optprobes for powerpc core |
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On Wed, 18 May 2016 02:09:37 +0530 Anju T <anju@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 <anju@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 <mhiramat@kernel.org>
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