[S390] kprobes: single step cleanup

The saved interrupt mask and the saved control registers are only
relevant while single stepping is set up. A secondary kprobe while
kprobe single stepping is active may not occur. That makes is safe
to remove the save and restore of kprobe_saved_imask / kprobe_save_ctl
from save_previous_kprobe and restore_previous_kprobe.
Move all single step related code to two functions, enable_singlestep
and disable_singlestep.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

2 files changed, 36 insertions, 44 deletions

diff --git a/arch/s390/include/asm/kprobes.h b/arch/s390/include/asm/kprobes.h
index 330f68caffe4..15d0dec8dbb4 100644
--- a/arch/s390/include/asm/kprobes.h
+++ b/arch/s390/include/asm/kprobes.h
@@ -72,9 +72,6 @@ struct ins_replace_args {
 struct prev_kprobe {
         struct kprobe *kp;
         unsigned long status;
-        unsigned long saved_psw;
-        unsigned long kprobe_saved_imask;
-        unsigned long kprobe_saved_ctl[3];
 };
 
 /* per-cpu kprobe control block */
diff --git a/arch/s390/kernel/kprobes.c b/arch/s390/kernel/kprobes.c
index b8e51759b6e4..91c611f84ff7 100644
--- a/arch/s390/kernel/kprobes.c
+++ b/arch/s390/kernel/kprobes.c
@@ -198,51 +198,58 @@ void __kprobes arch_remove_kprobe(struct kprobe *p)
         }
 }
 
-static void __kprobes prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
+static void __kprobes enable_singlestep(struct kprobe_ctlblk *kcb,
+                                        struct pt_regs *regs,
+                                        unsigned long ip)
 {
         per_cr_bits kprobe_per_regs[1];
 
-        memset(kprobe_per_regs, 0, sizeof(per_cr_bits));
-        regs->psw.addr = (unsigned long)p->ainsn.insn | PSW_ADDR_AMODE;
-
         /* Set up the per control reg info, will pass to lctl */
+        memset(kprobe_per_regs, 0, sizeof(per_cr_bits));
         kprobe_per_regs[0].em_instruction_fetch = 1;
-        kprobe_per_regs[0].starting_addr = (unsigned long)p->ainsn.insn;
-        kprobe_per_regs[0].ending_addr = (unsigned long)p->ainsn.insn + 1;
+        kprobe_per_regs[0].starting_addr = ip;
+        kprobe_per_regs[0].ending_addr = ip;
 
-        /* Set the PER control regs, turns on single step for this address */
+        /* Save control regs and psw mask */
+        __ctl_store(kcb->kprobe_saved_ctl, 9, 11);
+        kcb->kprobe_saved_imask = regs->psw.mask &
+                (PSW_MASK_PER | PSW_MASK_IO | PSW_MASK_EXT);
+
+        /* Set PER control regs, turns on single step for the given address */
         __ctl_load(kprobe_per_regs, 9, 11);
         regs->psw.mask |= PSW_MASK_PER;
         regs->psw.mask &= ~(PSW_MASK_IO | PSW_MASK_EXT);
+        regs->psw.addr = ip | PSW_ADDR_AMODE;
 }
 
+static void __kprobes disable_singlestep(struct kprobe_ctlblk *kcb,
+                                         struct pt_regs *regs,
+                                         unsigned long ip)
+{
+        /* Restore control regs and psw mask, set new psw address */
+        __ctl_load(kcb->kprobe_saved_ctl, 9, 11);
+        regs->psw.mask &= ~PSW_MASK_PER;
+        regs->psw.mask |= kcb->kprobe_saved_imask;
+        regs->psw.addr = ip | PSW_ADDR_AMODE;
+}
+
+
 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
 {
         kcb->prev_kprobe.kp = kprobe_running();
         kcb->prev_kprobe.status = kcb->kprobe_status;
-        kcb->prev_kprobe.kprobe_saved_imask = kcb->kprobe_saved_imask;
-        memcpy(kcb->prev_kprobe.kprobe_saved_ctl, kcb->kprobe_saved_ctl,
-                                        sizeof(kcb->kprobe_saved_ctl));
 }
 
 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
 {
         __get_cpu_var(current_kprobe) = kcb->prev_kprobe.kp;
         kcb->kprobe_status = kcb->prev_kprobe.status;
-        kcb->kprobe_saved_imask = kcb->prev_kprobe.kprobe_saved_imask;
-        memcpy(kcb->kprobe_saved_ctl, kcb->prev_kprobe.kprobe_saved_ctl,
-                                        sizeof(kcb->kprobe_saved_ctl));
 }
 
 static void __kprobes set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
                                                 struct kprobe_ctlblk *kcb)
 {
         __get_cpu_var(current_kprobe) = p;
-        /* Save the interrupt and per flags */
-        kcb->kprobe_saved_imask = regs->psw.mask &
-                (PSW_MASK_PER | PSW_MASK_IO | PSW_MASK_EXT);
-        /* Save the control regs that govern PER */
-        __ctl_store(kcb->kprobe_saved_ctl, 9, 11);
 }
 
 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
@@ -282,7 +289,8 @@ static int __kprobes kprobe_handler(struct pt_regs *regs)
                         save_previous_kprobe(kcb);
                         set_current_kprobe(p, regs, kcb);
                         kprobes_inc_nmissed_count(p);
-                        prepare_singlestep(p, regs);
+                        enable_singlestep(kcb, regs,
+                                          (unsigned long) p->ainsn.insn);
                         kcb->kprobe_status = KPROBE_REENTER;
                         return 1;
                 } else {
@@ -311,7 +319,7 @@ static int __kprobes kprobe_handler(struct pt_regs *regs)
                 return 1;
 
 ss_probe:
-        prepare_singlestep(p, regs);
+        enable_singlestep(kcb, regs, (unsigned long) p->ainsn.insn);
         kcb->kprobe_status = KPROBE_HIT_SS;
         return 1;
 
@@ -433,31 +441,20 @@ static int __kprobes trampoline_probe_handler(struct kprobe *p,
 static void __kprobes resume_execution(struct kprobe *p, struct pt_regs *regs)
 {
         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
-
-        regs->psw.addr &= PSW_ADDR_INSN;
+        unsigned long ip = regs->psw.addr & PSW_ADDR_INSN;
 
         if (p->ainsn.fixup & FIXUP_PSW_NORMAL)
-                regs->psw.addr = (unsigned long)p->addr +
-                                ((unsigned long)regs->psw.addr -
-                                 (unsigned long)p->ainsn.insn);
+                ip += (unsigned long) p->addr - (unsigned long) p->ainsn.insn;
 
         if (p->ainsn.fixup & FIXUP_BRANCH_NOT_TAKEN)
-                if ((unsigned long)regs->psw.addr -
-                    (unsigned long)p->ainsn.insn == p->ainsn.ilen)
-                        regs->psw.addr = (unsigned long)p->addr + p->ainsn.ilen;
+                if (ip - (unsigned long) p->ainsn.insn == p->ainsn.ilen)
+                        ip = (unsigned long) p->addr + p->ainsn.ilen;
 
         if (p->ainsn.fixup & FIXUP_RETURN_REGISTER)
-                regs->gprs[p->ainsn.reg] = ((unsigned long)p->addr +
-                                                (regs->gprs[p->ainsn.reg] -
-                                                (unsigned long)p->ainsn.insn))
-                                                | PSW_ADDR_AMODE;
+                regs->gprs[p->ainsn.reg] += (unsigned long) p->addr -
+                                            (unsigned long) p->ainsn.insn;
 
-        regs->psw.addr |= PSW_ADDR_AMODE;
-        /* turn off PER mode */
-        regs->psw.mask &= ~PSW_MASK_PER;
-        /* Restore the original per control regs */
-        __ctl_load(kcb->kprobe_saved_ctl, 9, 11);
-        regs->psw.mask |= kcb->kprobe_saved_imask;
+        disable_singlestep(kcb, regs, ip);
 }
 
 static int __kprobes post_kprobe_handler(struct pt_regs *regs)
@@ -515,9 +512,7 @@ static int __kprobes kprobe_trap_handler(struct pt_regs *regs, int trapnr)
                  * and allow the page fault handler to continue as a
                  * normal page fault.
                  */
-                regs->psw.addr = (unsigned long)cur->addr | PSW_ADDR_AMODE;
-                regs->psw.mask &= ~PSW_MASK_PER;
-                regs->psw.mask |= kcb->kprobe_saved_imask;
+                disable_singlestep(kcb, regs, (unsigned long) cur->addr);
                 if (kcb->kprobe_status == KPROBE_REENTER)
                         restore_previous_kprobe(kcb);
                 else {