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[S390] Minor fault path optimization.
The minor fault path has grown a lot in terms of cycles. In particular the kprobes hook is very costly. Optimize the path to save a couple of cycles. If kprobes is enabled more than 300 cycles can be avoided if kprobes_running() is false. Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com> Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
This commit is contained in:
Martin Schwidefsky
parent
c0007f1a65
commit
10c1031f70
@ -63,21 +63,25 @@ int unregister_page_fault_notifier(struct notifier_block *nb)
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return atomic_notifier_chain_unregister(¬ify_page_fault_chain, nb);
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}
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static inline int notify_page_fault(enum die_val val, const char *str,
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struct pt_regs *regs, long err, int trap, int sig)
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static int __kprobes __notify_page_fault(struct pt_regs *regs, long err)
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{
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struct die_args args = {
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.regs = regs,
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.str = str,
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.err = err,
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.trapnr = trap,
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.signr = sig
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};
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return atomic_notifier_call_chain(¬ify_page_fault_chain, val, &args);
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struct die_args args = { .str = "page fault",
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.trapnr = 14,
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.signr = SIGSEGV };
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args.regs = regs;
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args.err = err;
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return atomic_notifier_call_chain(¬ify_page_fault_chain,
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DIE_PAGE_FAULT, &args);
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}
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static inline int notify_page_fault(struct pt_regs *regs, long err)
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{
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if (unlikely(kprobe_running()))
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return __notify_page_fault(regs, err);
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return NOTIFY_DONE;
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}
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#else
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static inline int notify_page_fault(enum die_val val, const char *str,
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struct pt_regs *regs, long err, int trap, int sig)
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static inline int notify_page_fault(struct pt_regs *regs, long err)
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{
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return NOTIFY_DONE;
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}
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@ -170,6 +174,89 @@ static void do_sigsegv(struct pt_regs *regs, unsigned long error_code,
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force_sig_info(SIGSEGV, &si, current);
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}
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static void do_no_context(struct pt_regs *regs, unsigned long error_code,
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unsigned long address)
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{
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const struct exception_table_entry *fixup;
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/* Are we prepared to handle this kernel fault? */
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fixup = search_exception_tables(regs->psw.addr & __FIXUP_MASK);
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if (fixup) {
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regs->psw.addr = fixup->fixup | PSW_ADDR_AMODE;
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return;
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}
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/*
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* Oops. The kernel tried to access some bad page. We'll have to
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* terminate things with extreme prejudice.
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*/
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if (check_space(current) == 0)
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printk(KERN_ALERT "Unable to handle kernel pointer dereference"
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" at virtual kernel address %p\n", (void *)address);
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else
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printk(KERN_ALERT "Unable to handle kernel paging request"
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" at virtual user address %p\n", (void *)address);
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die("Oops", regs, error_code);
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do_exit(SIGKILL);
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}
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static void do_low_address(struct pt_regs *regs, unsigned long error_code)
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{
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/* Low-address protection hit in kernel mode means
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NULL pointer write access in kernel mode. */
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if (regs->psw.mask & PSW_MASK_PSTATE) {
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/* Low-address protection hit in user mode 'cannot happen'. */
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die ("Low-address protection", regs, error_code);
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do_exit(SIGKILL);
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}
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do_no_context(regs, error_code, 0);
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}
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/*
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* We ran out of memory, or some other thing happened to us that made
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* us unable to handle the page fault gracefully.
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*/
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static int do_out_of_memory(struct pt_regs *regs, unsigned long error_code,
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unsigned long address)
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{
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struct task_struct *tsk = current;
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struct mm_struct *mm = tsk->mm;
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up_read(&mm->mmap_sem);
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if (is_init(tsk)) {
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yield();
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down_read(&mm->mmap_sem);
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return 1;
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}
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printk("VM: killing process %s\n", tsk->comm);
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if (regs->psw.mask & PSW_MASK_PSTATE)
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do_exit(SIGKILL);
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do_no_context(regs, error_code, address);
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return 0;
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}
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static void do_sigbus(struct pt_regs *regs, unsigned long error_code,
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unsigned long address)
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{
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struct task_struct *tsk = current;
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struct mm_struct *mm = tsk->mm;
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up_read(&mm->mmap_sem);
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/*
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* Send a sigbus, regardless of whether we were in kernel
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* or user mode.
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*/
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tsk->thread.prot_addr = address;
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tsk->thread.trap_no = error_code;
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force_sig(SIGBUS, tsk);
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/* Kernel mode? Handle exceptions or die */
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if (!(regs->psw.mask & PSW_MASK_PSTATE))
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do_no_context(regs, error_code, address);
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}
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#ifdef CONFIG_S390_EXEC_PROTECT
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extern long sys_sigreturn(struct pt_regs *regs);
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extern long sys_rt_sigreturn(struct pt_regs *regs);
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@ -253,49 +340,23 @@ out_fault:
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* 3b Region third trans. -> Not present (nullification)
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*/
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static inline void
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do_exception(struct pt_regs *regs, unsigned long error_code, int is_protection)
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do_exception(struct pt_regs *regs, unsigned long error_code, int write)
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{
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struct task_struct *tsk;
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struct mm_struct *mm;
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struct vm_area_struct * vma;
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unsigned long address;
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const struct exception_table_entry *fixup;
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int si_code;
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struct task_struct *tsk;
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struct mm_struct *mm;
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struct vm_area_struct *vma;
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unsigned long address;
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int space;
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int si_code;
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tsk = current;
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mm = tsk->mm;
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if (notify_page_fault(DIE_PAGE_FAULT, "page fault", regs, error_code, 14,
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SIGSEGV) == NOTIFY_STOP)
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if (notify_page_fault(regs, error_code) == NOTIFY_STOP)
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return;
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/*
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* Check for low-address protection. This needs to be treated
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* as a special case because the translation exception code
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* field is not guaranteed to contain valid data in this case.
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*/
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if (is_protection && !(S390_lowcore.trans_exc_code & 4)) {
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tsk = current;
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mm = tsk->mm;
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/* Low-address protection hit in kernel mode means
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NULL pointer write access in kernel mode. */
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if (!(regs->psw.mask & PSW_MASK_PSTATE)) {
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address = 0;
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space = 0;
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goto no_context;
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}
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/* Low-address protection hit in user mode 'cannot happen'. */
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die ("Low-address protection", regs, error_code);
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do_exit(SIGKILL);
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}
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/*
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* get the failing address
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* more specific the segment and page table portion of
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* the address
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*/
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address = S390_lowcore.trans_exc_code & __FAIL_ADDR_MASK;
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/* get the failing address and the affected space */
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address = S390_lowcore.trans_exc_code & __FAIL_ADDR_MASK;
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space = check_space(tsk);
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/*
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@ -313,7 +374,7 @@ do_exception(struct pt_regs *regs, unsigned long error_code, int is_protection)
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*/
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local_irq_enable();
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down_read(&mm->mmap_sem);
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down_read(&mm->mmap_sem);
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si_code = SEGV_MAPERR;
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vma = find_vma(mm, address);
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@ -330,19 +391,19 @@ do_exception(struct pt_regs *regs, unsigned long error_code, int is_protection)
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return;
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#endif
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if (vma->vm_start <= address)
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goto good_area;
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if (!(vma->vm_flags & VM_GROWSDOWN))
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goto bad_area;
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if (expand_stack(vma, address))
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goto bad_area;
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if (vma->vm_start <= address)
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goto good_area;
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if (!(vma->vm_flags & VM_GROWSDOWN))
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goto bad_area;
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if (expand_stack(vma, address))
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goto bad_area;
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/*
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* Ok, we have a good vm_area for this memory access, so
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* we can handle it..
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*/
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good_area:
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si_code = SEGV_ACCERR;
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if (!is_protection) {
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if (!write) {
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/* page not present, check vm flags */
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if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
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goto bad_area;
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@ -357,7 +418,7 @@ survive:
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* make sure we exit gracefully rather than endlessly redo
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* the fault.
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*/
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switch (handle_mm_fault(mm, vma, address, is_protection)) {
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switch (handle_mm_fault(mm, vma, address, write)) {
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case VM_FAULT_MINOR:
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tsk->min_flt++;
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break;
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@ -365,9 +426,12 @@ survive:
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tsk->maj_flt++;
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break;
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case VM_FAULT_SIGBUS:
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goto do_sigbus;
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do_sigbus(regs, error_code, address);
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return;
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case VM_FAULT_OOM:
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goto out_of_memory;
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if (do_out_of_memory(regs, error_code, address))
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goto survive;
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return;
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default:
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BUG();
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}
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@ -385,75 +449,34 @@ survive:
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* Fix it, but check if it's kernel or user first..
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*/
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bad_area:
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up_read(&mm->mmap_sem);
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up_read(&mm->mmap_sem);
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/* User mode accesses just cause a SIGSEGV */
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if (regs->psw.mask & PSW_MASK_PSTATE) {
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tsk->thread.prot_addr = address;
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tsk->thread.trap_no = error_code;
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/* User mode accesses just cause a SIGSEGV */
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if (regs->psw.mask & PSW_MASK_PSTATE) {
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tsk->thread.prot_addr = address;
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tsk->thread.trap_no = error_code;
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do_sigsegv(regs, error_code, si_code, address);
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return;
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return;
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}
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no_context:
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/* Are we prepared to handle this kernel fault? */
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fixup = search_exception_tables(regs->psw.addr & __FIXUP_MASK);
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if (fixup) {
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regs->psw.addr = fixup->fixup | PSW_ADDR_AMODE;
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return;
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}
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/*
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* Oops. The kernel tried to access some bad page. We'll have to
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* terminate things with extreme prejudice.
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*/
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if (space == 0)
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printk(KERN_ALERT "Unable to handle kernel pointer dereference"
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" at virtual kernel address %p\n", (void *)address);
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else
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printk(KERN_ALERT "Unable to handle kernel paging request"
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" at virtual user address %p\n", (void *)address);
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die("Oops", regs, error_code);
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do_exit(SIGKILL);
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/*
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* We ran out of memory, or some other thing happened to us that made
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* us unable to handle the page fault gracefully.
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*/
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out_of_memory:
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up_read(&mm->mmap_sem);
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if (is_init(tsk)) {
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yield();
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down_read(&mm->mmap_sem);
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goto survive;
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}
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printk("VM: killing process %s\n", tsk->comm);
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if (regs->psw.mask & PSW_MASK_PSTATE)
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do_exit(SIGKILL);
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goto no_context;
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do_sigbus:
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up_read(&mm->mmap_sem);
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/*
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* Send a sigbus, regardless of whether we were in kernel
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* or user mode.
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*/
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tsk->thread.prot_addr = address;
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tsk->thread.trap_no = error_code;
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force_sig(SIGBUS, tsk);
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/* Kernel mode? Handle exceptions or die */
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if (!(regs->psw.mask & PSW_MASK_PSTATE))
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goto no_context;
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do_no_context(regs, error_code, address);
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}
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void __kprobes do_protection_exception(struct pt_regs *regs,
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unsigned long error_code)
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{
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/* Protection exception is supressing, decrement psw address. */
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regs->psw.addr -= (error_code >> 16);
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/*
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* Check for low-address protection. This needs to be treated
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* as a special case because the translation exception code
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* field is not guaranteed to contain valid data in this case.
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*/
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if (unlikely(!(S390_lowcore.trans_exc_code & 4))) {
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do_low_address(regs, error_code);
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return;
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}
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do_exception(regs, 4, 1);
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}
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