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Subject[patch 04/52] [PATCH] fault handler performance optimization.
From: Martin Schwidefsky <schwidefsky@de.ibm.com>

Slim down the do_exception function to handle only the fast path of a
fault and move the exceptional cases into a new function. That slightly
increases the performance of the fault handling.

Build fix for !CONFIG_COMPAT by
Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---
arch/s390/mm/fault.c | 258 +++++++++++++++++++++++++--------------------------
1 file changed, 129 insertions(+), 129 deletions(-)
Index: quilt-2.6/arch/s390/mm/fault.c
===================================================================
--- quilt-2.6.orig/arch/s390/mm/fault.c 2009-11-13 16:08:12.000000000 +0100
+++ quilt-2.6/arch/s390/mm/fault.c 2009-11-13 16:08:12.000000000 +0100
@@ -34,16 +34,15 @@
#include <asm/pgtable.h>
#include <asm/s390_ext.h>
#include <asm/mmu_context.h>
+#include <asm/compat.h>
#include "../kernel/entry.h"

#ifndef CONFIG_64BIT
#define __FAIL_ADDR_MASK 0x7ffff000
-#define __FIXUP_MASK 0x7fffffff
#define __SUBCODE_MASK 0x0200
#define __PF_RES_FIELD 0ULL
#else /* CONFIG_64BIT */
#define __FAIL_ADDR_MASK -4096L
-#define __FIXUP_MASK ~0L
#define __SUBCODE_MASK 0x0600
#define __PF_RES_FIELD 0x8000000000000000ULL
#endif /* CONFIG_64BIT */
@@ -52,6 +51,10 @@
extern int sysctl_userprocess_debug;
#endif

+#define VM_FAULT_BADCONTEXT 0x010000
+#define VM_FAULT_BADMAP 0x020000
+#define VM_FAULT_BADACCESS 0x040000
+
static inline int notify_page_fault(struct pt_regs *regs)
{
int ret = 0;
@@ -122,18 +125,22 @@
* Send SIGSEGV to task. This is an external routine
* to keep the stack usage of do_page_fault small.
*/
-static void do_sigsegv(struct pt_regs *regs, unsigned long error_code,
- int si_code, unsigned long address)
+static noinline void do_sigsegv(struct pt_regs *regs, long int_code,
+ int si_code, unsigned long trans_exc_code)
{
struct siginfo si;
+ unsigned long address;

+ address = trans_exc_code & __FAIL_ADDR_MASK;
+ current->thread.prot_addr = address;
+ current->thread.trap_no = int_code;
#if defined(CONFIG_SYSCTL) || defined(CONFIG_PROCESS_DEBUG)
#if defined(CONFIG_SYSCTL)
if (sysctl_userprocess_debug)
#endif
{
printk("User process fault: interruption code 0x%lX\n",
- error_code);
+ int_code);
printk("failing address: %lX\n", address);
show_regs(regs);
}
@@ -144,14 +151,14 @@
force_sig_info(SIGSEGV, &si, current);
}

-static void do_no_context(struct pt_regs *regs, unsigned long error_code,
- unsigned long trans_exc_code)
+static noinline void do_no_context(struct pt_regs *regs, long int_code,
+ unsigned long trans_exc_code)
{
const struct exception_table_entry *fixup;
unsigned long address;

/* Are we prepared to handle this kernel fault? */
- fixup = search_exception_tables(regs->psw.addr & __FIXUP_MASK);
+ fixup = search_exception_tables(regs->psw.addr & PSW_ADDR_INSN);
if (fixup) {
regs->psw.addr = fixup->fixup | PSW_ADDR_AMODE;
return;
@@ -169,107 +176,127 @@
printk(KERN_ALERT "Unable to handle kernel paging request"
" at virtual user address %p\n", (void *)address);

- die("Oops", regs, error_code);
+ die("Oops", regs, int_code);
do_exit(SIGKILL);
}

-static void do_low_address(struct pt_regs *regs, unsigned long error_code,
- unsigned long trans_exc_code)
+static noinline void do_low_address(struct pt_regs *regs, long int_code,
+ unsigned long trans_exc_code)
{
/* Low-address protection hit in kernel mode means
NULL pointer write access in kernel mode. */
if (regs->psw.mask & PSW_MASK_PSTATE) {
/* Low-address protection hit in user mode 'cannot happen'. */
- die ("Low-address protection", regs, error_code);
+ die ("Low-address protection", regs, int_code);
do_exit(SIGKILL);
}

- do_no_context(regs, error_code, trans_exc_code);
+ do_no_context(regs, int_code, trans_exc_code);
}

-static void do_sigbus(struct pt_regs *regs, unsigned long error_code,
- unsigned long trans_exc_code)
+static noinline void do_sigbus(struct pt_regs *regs, long int_code,
+ unsigned long trans_exc_code)
{
struct task_struct *tsk = current;
- struct mm_struct *mm = tsk->mm;

- up_read(&mm->mmap_sem);
/*
* Send a sigbus, regardless of whether we were in kernel
* or user mode.
*/
tsk->thread.prot_addr = trans_exc_code & __FAIL_ADDR_MASK;
- tsk->thread.trap_no = error_code;
+ tsk->thread.trap_no = int_code;
force_sig(SIGBUS, tsk);
-
- /* Kernel mode? Handle exceptions or die */
- if (!(regs->psw.mask & PSW_MASK_PSTATE))
- do_no_context(regs, error_code, trans_exc_code);
}

#ifdef CONFIG_S390_EXEC_PROTECT
-static int signal_return(struct mm_struct *mm, struct pt_regs *regs,
- unsigned long address, unsigned long error_code)
+static noinline int signal_return(struct pt_regs *regs, long int_code,
+ unsigned long trans_exc_code)
{
u16 instruction;
int rc;
-#ifdef CONFIG_COMPAT
- int compat;
-#endif

- pagefault_disable();
rc = __get_user(instruction, (u16 __user *) regs->psw.addr);
- pagefault_enable();
- if (rc)
- return -EFAULT;

- up_read(&mm->mmap_sem);
- clear_tsk_thread_flag(current, TIF_SINGLE_STEP);
-#ifdef CONFIG_COMPAT
- compat = is_compat_task();
- if (compat && instruction == 0x0a77)
- sys32_sigreturn();
- else if (compat && instruction == 0x0aad)
- sys32_rt_sigreturn();
- else
-#endif
- if (instruction == 0x0a77)
- sys_sigreturn();
- else if (instruction == 0x0aad)
- sys_rt_sigreturn();
- else {
- current->thread.prot_addr = address;
- current->thread.trap_no = error_code;
- do_sigsegv(regs, error_code, SEGV_MAPERR, address);
- }
+ if (!rc && instruction == 0x0a77) {
+ clear_tsk_thread_flag(current, TIF_SINGLE_STEP);
+ if (is_compat_task())
+ sys32_sigreturn();
+ else
+ sys_sigreturn();
+ } else if (!rc && instruction == 0x0aad) {
+ clear_tsk_thread_flag(current, TIF_SINGLE_STEP);
+ if (is_compat_task())
+ sys32_rt_sigreturn();
+ else
+ sys_rt_sigreturn();
+ } else
+ do_sigsegv(regs, int_code, SEGV_MAPERR, trans_exc_code);
return 0;
}
#endif /* CONFIG_S390_EXEC_PROTECT */

+static noinline void do_fault_error(struct pt_regs *regs, long int_code,
+ unsigned long trans_exc_code, int fault)
+{
+ int si_code;
+
+ switch (fault) {
+ case VM_FAULT_BADACCESS:
+#ifdef CONFIG_S390_EXEC_PROTECT
+ if ((regs->psw.mask & PSW_MASK_ASC) == PSW_ASC_SECONDARY &&
+ (trans_exc_code & 3) == 0) {
+ signal_return(regs, int_code, trans_exc_code);
+ break;
+ }
+#endif /* CONFIG_S390_EXEC_PROTECT */
+ case VM_FAULT_BADMAP:
+ /* Bad memory access. Check if it is kernel or user space. */
+ if (regs->psw.mask & PSW_MASK_PSTATE) {
+ /* User mode accesses just cause a SIGSEGV */
+ si_code = (fault == VM_FAULT_BADMAP) ?
+ SEGV_MAPERR : SEGV_ACCERR;
+ do_sigsegv(regs, int_code, si_code, trans_exc_code);
+ return;
+ }
+ case VM_FAULT_BADCONTEXT:
+ do_no_context(regs, int_code, trans_exc_code);
+ break;
+ default: /* fault & VM_FAULT_ERROR */
+ if (fault & VM_FAULT_OOM)
+ pagefault_out_of_memory();
+ else if (fault & VM_FAULT_SIGBUS) {
+ do_sigbus(regs, int_code, trans_exc_code);
+ /* Kernel mode? Handle exceptions or die */
+ if (!(regs->psw.mask & PSW_MASK_PSTATE))
+ do_no_context(regs, int_code, trans_exc_code);
+ } else
+ BUG();
+ break;
+ }
+}
+
/*
* This routine handles page faults. It determines the address,
* and the problem, and then passes it off to one of the appropriate
* routines.
*
- * error_code:
+ * interruption code (int_code):
* 04 Protection -> Write-Protection (suprression)
* 10 Segment translation -> Not present (nullification)
* 11 Page translation -> Not present (nullification)
* 3b Region third trans. -> Not present (nullification)
*/
-static inline void
-do_exception(struct pt_regs *regs, unsigned long error_code, int write,
- unsigned long trans_exc_code)
+static inline int do_exception(struct pt_regs *regs, int write,
+ unsigned long trans_exc_code)
{
struct task_struct *tsk;
struct mm_struct *mm;
struct vm_area_struct *vma;
unsigned long address;
- int si_code;
int fault;

if (notify_page_fault(regs))
- return;
+ return 0;

tsk = current;
mm = tsk->mm;
@@ -279,8 +306,9 @@
* we are not in an interrupt and that there is a
* user context.
*/
+ fault = VM_FAULT_BADCONTEXT;
if (unlikely(!user_space_fault(trans_exc_code) || in_atomic() || !mm))
- goto no_context;
+ goto out;

address = trans_exc_code & __FAIL_ADDR_MASK;
/*
@@ -292,41 +320,35 @@
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, 0, regs, address);
down_read(&mm->mmap_sem);

- si_code = SEGV_MAPERR;
+ fault = VM_FAULT_BADMAP;
vma = find_vma(mm, address);
if (!vma)
- goto bad_area;
+ goto out_up;

+ if (unlikely(vma->vm_start > address)) {
+ if (!(vma->vm_flags & VM_GROWSDOWN))
+ goto out_up;
+ if (expand_stack(vma, address))
+ goto out_up;
+ }
+
+ /*
+ * Ok, we have a good vm_area for this memory access, so
+ * we can handle it..
+ */
+ fault = VM_FAULT_BADACCESS;
#ifdef CONFIG_S390_EXEC_PROTECT
if (unlikely((regs->psw.mask & PSW_MASK_ASC) == PSW_ASC_SECONDARY &&
(trans_exc_code & 3) == 0 && !(vma->vm_flags & VM_EXEC)))
- if (!signal_return(mm, regs, address, error_code))
- /*
- * signal_return() has done an up_read(&mm->mmap_sem)
- * if it returns 0.
- */
- return;
+ goto out_up;
#endif
-
- if (vma->vm_start <= address)
- goto good_area;
- if (!(vma->vm_flags & VM_GROWSDOWN))
- goto bad_area;
- if (expand_stack(vma, address))
- goto bad_area;
-/*
- * Ok, we have a good vm_area for this memory access, so
- * we can handle it..
- */
-good_area:
- si_code = SEGV_ACCERR;
if (!write) {
/* page not present, check vm flags */
if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
- goto bad_area;
+ goto out_up;
} else {
if (!(vma->vm_flags & VM_WRITE))
- goto bad_area;
+ goto out_up;
}

if (is_vm_hugetlb_page(vma))
@@ -337,17 +359,9 @@
* the fault.
*/
fault = handle_mm_fault(mm, vma, address, write ? FAULT_FLAG_WRITE : 0);
- if (unlikely(fault & VM_FAULT_ERROR)) {
- if (fault & VM_FAULT_OOM) {
- up_read(&mm->mmap_sem);
- pagefault_out_of_memory();
- return;
- } else if (fault & VM_FAULT_SIGBUS) {
- do_sigbus(regs, error_code, address);
- return;
- }
- BUG();
- }
+ if (unlikely(fault & VM_FAULT_ERROR))
+ goto out_up;
+
if (fault & VM_FAULT_MAJOR) {
tsk->maj_flt++;
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, 0,
@@ -357,67 +371,55 @@
perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, 0,
regs, address);
}
- up_read(&mm->mmap_sem);
/*
* The instruction that caused the program check will
* be repeated. Don't signal single step via SIGTRAP.
*/
clear_tsk_thread_flag(tsk, TIF_SINGLE_STEP);
- return;
-
-/*
- * Something tried to access memory that isn't in our memory map..
- * Fix it, but check if it's kernel or user first..
- */
-bad_area:
+ fault = 0;
+out_up:
up_read(&mm->mmap_sem);
-
- /* User mode accesses just cause a SIGSEGV */
- if (regs->psw.mask & PSW_MASK_PSTATE) {
- tsk->thread.prot_addr = address;
- tsk->thread.trap_no = error_code;
- do_sigsegv(regs, error_code, si_code, address);
- return;
- }
-
-no_context:
- do_no_context(regs, error_code, trans_exc_code);
+out:
+ return fault;
}

-void __kprobes do_protection_exception(struct pt_regs *regs,
- long error_code)
+void __kprobes do_protection_exception(struct pt_regs *regs, long int_code)
{
unsigned long trans_exc_code = S390_lowcore.trans_exc_code;
+ int fault;

/* Protection exception is supressing, decrement psw address. */
- regs->psw.addr -= (error_code >> 16);
+ regs->psw.addr -= (int_code >> 16);
/*
* Check for low-address protection. This needs to be treated
* as a special case because the translation exception code
* field is not guaranteed to contain valid data in this case.
*/
if (unlikely(!(trans_exc_code & 4))) {
- do_low_address(regs, error_code, trans_exc_code);
+ do_low_address(regs, int_code, trans_exc_code);
return;
}
- do_exception(regs, 4, 1, trans_exc_code);
+ fault = do_exception(regs, 1, trans_exc_code);
+ if (unlikely(fault))
+ do_fault_error(regs, 4, trans_exc_code, fault);
}

-void __kprobes do_dat_exception(struct pt_regs *regs, long error_code)
+void __kprobes do_dat_exception(struct pt_regs *regs, long int_code)
{
- do_exception(regs, error_code & 0xff, 0, S390_lowcore.trans_exc_code);
+ unsigned long trans_exc_code = S390_lowcore.trans_exc_code;
+ int fault;
+
+ fault = do_exception(regs, 0, trans_exc_code);
+ if (unlikely(fault))
+ do_fault_error(regs, int_code & 255, trans_exc_code, fault);
}

#ifdef CONFIG_64BIT
-void __kprobes do_asce_exception(struct pt_regs *regs, unsigned long error_code)
+void __kprobes do_asce_exception(struct pt_regs *regs, long int_code)
{
unsigned long trans_exc_code = S390_lowcore.trans_exc_code;
- struct mm_struct *mm;
+ struct mm_struct *mm = current->mm;
struct vm_area_struct *vma;
- unsigned long address;
-
- mm = current->mm;
- address = trans_exc_code & __FAIL_ADDR_MASK;

if (unlikely(!user_space_fault(trans_exc_code) || in_atomic() || !mm))
goto no_context;
@@ -425,7 +427,7 @@
local_irq_enable();

down_read(&mm->mmap_sem);
- vma = find_vma(mm, address);
+ vma = find_vma(mm, trans_exc_code & __FAIL_ADDR_MASK);
up_read(&mm->mmap_sem);

if (vma) {
@@ -435,14 +437,12 @@

/* User mode accesses just cause a SIGSEGV */
if (regs->psw.mask & PSW_MASK_PSTATE) {
- current->thread.prot_addr = address;
- current->thread.trap_no = error_code;
- do_sigsegv(regs, error_code, SEGV_MAPERR, address);
+ do_sigsegv(regs, int_code, SEGV_MAPERR, trans_exc_code);
return;
}

no_context:
- do_no_context(regs, error_code, trans_exc_code);
+ do_no_context(regs, int_code, trans_exc_code);
}
#endif

@@ -507,7 +507,7 @@
: : "a" (&refbk), "m" (refbk) : "cc");
}

-static void pfault_interrupt(__u16 error_code)
+static void pfault_interrupt(__u16 int_code)
{
struct task_struct *tsk;
__u16 subcode;


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