Re: [RFC PATCH 2/3] arch/powerpc : optprobes for powerpc core
From: Anju T
Date: Thu May 19 2016 - 03:50:05 EST
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@xxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxx>
---
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!