Re: [RFC PATCH 2/3] arch/powerpc : optprobes for powerpc core

[Anju T <anju@linux.vnet.ibm.com>]

Hi Masami,

  Thank you for reviewing the patch.

On Wednesday 18 May 2016 08:43 PM, Masami Hiramatsu wrote:
> 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?

Yes. Will do.
>> +
>> +#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.

Ok.
>
>> +
>> +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().

OK. Will do.
>
>> +
>> +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...

Sure :-)

>> +}
>> +
>> +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?

Yes. will declare it as 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?

Will remove this 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.

Sure.
>
>> +	}
>> +}
>> +
>> +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.

The only case this check will succeed is if kp.addr is not a multiple of 4, which is not a valid address at all on
Power.So should we again check here for that?




Thanks and Regards

-Anju



>> +	return 0;
>> +}
>> -- 
>> 2.1.0
>>
> Thanks!
>