x86, mm: fault.c cleanup

Impact: cleanup, no code changed

Clean up various small details, which can be correctness checked
automatically:

 - tidy up the include file section
 - eliminate unnecessary includes
 - introduce show_signal_msg() to clean up code flow
 - standardize the code flow
 - standardize comments and other style details
 - more cleanups, pointed out by checkpatch

No code changed on either 32-bit nor 64-bit:

arch/x86/mm/fault.o:

   text	   data	    bss	    dec	    hex	filename
   4632	     32	     24	   4688	   1250	fault.o.before
   4632	     32	     24	   4688	   1250	fault.o.after

the md5 changed due to a change in a single instruction:

   2e8a8241e7f0d69706776a5a26c90bc0  fault.o.before.asm
   c5c3d36e725586eb74f0e10692f0193e  fault.o.after.asm

Because a __LINE__ reference in a WARN_ONCE() has changed.

On 32-bit a few stack offsets changed - no code size difference
nor any functionality difference.

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/mm/fault.c

 /*
  *  Copyright (C) 1995  Linus Torvalds
- *  Copyright (C) 2001,2002 Andi Kleen, SuSE Labs.
+ *  Copyright (C) 2001, 2002 Andi Kleen, SuSE Labs.
  */
-
-#include <linux/signal.h>
-#include <linux/sched.h>
-#include <linux/kernel.h>
-#include <linux/errno.h>
-#include <linux/string.h>
-#include <linux/types.h>
-#include <linux/ptrace.h>
-#include <linux/mmiotrace.h>
-#include <linux/mman.h>
-#include <linux/mm.h>
-#include <linux/smp.h>
 #include <linux/interrupt.h>
-#include <linux/init.h>
-#include <linux/tty.h>
-#include <linux/vt_kern.h>		/* For unblank_screen() */
+#include <linux/mmiotrace.h>
+#include <linux/bootmem.h>
 #include <linux/compiler.h>
 #include <linux/highmem.h>
-#include <linux/bootmem.h>		/* for max_low_pfn */
-#include <linux/vmalloc.h>
-#include <linux/module.h>
 #include <linux/kprobes.h>
 #include <linux/uaccess.h>
+#include <linux/vmalloc.h>
+#include <linux/vt_kern.h>
+#include <linux/signal.h>
+#include <linux/kernel.h>
+#include <linux/ptrace.h>
+#include <linux/string.h>
+#include <linux/module.h>
 #include <linux/kdebug.h>
+#include <linux/errno.h>
 #include <linux/magic.h>
+#include <linux/sched.h>
+#include <linux/types.h>
+#include <linux/init.h>
+#include <linux/mman.h>
+#include <linux/tty.h>
+#include <linux/smp.h>
+#include <linux/mm.h>
+
+#include <asm-generic/sections.h>
 
-#include <asm/system.h>
-#include <asm/desc.h>
-#include <asm/segment.h>
-#include <asm/pgalloc.h>
-#include <asm/smp.h>
 #include <asm/tlbflush.h>
+#include <asm/pgalloc.h>
+#include <asm/segment.h>
+#include <asm/system.h>
 #include <asm/proto.h>
-#include <asm-generic/sections.h>
 #include <asm/traps.h>
+#include <asm/desc.h>
 
 /*
- * Page fault error code bits
- *	bit 0 == 0 means no page found, 1 means protection fault
- *	bit 1 == 0 means read, 1 means write
- *	bit 2 == 0 means kernel, 1 means user-mode
- *	bit 3 == 1 means use of reserved bit detected
- *	bit 4 == 1 means fault was an instruction fetch
+ * Page fault error code bits:
+ *
+ *   bit 0 ==	 0: no page found	1: protection fault
+ *   bit 1 ==	 0: read access		1: write access
+ *   bit 2 ==	 0: kernel-mode access	1: user-mode access
+ *   bit 3 ==				1: use of reserved bit detected
+ *   bit 4 ==				1: fault was an instruction fetch
  */
-#define PF_PROT		(1<<0)
-#define PF_WRITE	(1<<1)
-#define PF_USER		(1<<2)
-#define PF_RSVD		(1<<3)
-#define PF_INSTR	(1<<4)
+enum x86_pf_error_code {
+
+	PF_PROT		=		1 << 0,
+	PF_WRITE	=		1 << 1,
+	PF_USER		=		1 << 2,
+	PF_RSVD		=		1 << 3,
+	PF_INSTR	=		1 << 4,
+};
 
 static inline int kmmio_fault(struct pt_regs *regs, unsigned long addr)
 {
@@ -82,23 +85,27 @@ static inline int notify_page_fault(struct pt_regs *regs)
 }
 
 /*
- * X86_32
+ * Prefetch quirks:
+ *
+ * 32-bit mode:
+ *
  *   Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch.
  *   Check that here and ignore it.
  *
- * X86_64
+ * 64-bit mode:
+ *
  *   Sometimes the CPU reports invalid exceptions on prefetch.
  *   Check that here and ignore it.
  *
- * Opcode checker based on code by Richard Brunner
+ * Opcode checker based on code by Richard Brunner.
  */
-static int is_prefetch(struct pt_regs *regs, unsigned long error_code,
-			unsigned long addr)
+static int
+is_prefetch(struct pt_regs *regs, unsigned long error_code, unsigned long addr)
 {
+	unsigned char *max_instr;
 	unsigned char *instr;
 	int scan_more = 1;
 	int prefetch = 0;
-	unsigned char *max_instr;
 
 	/*
 	 * If it was a exec (instruction fetch) fault on NX page, then
@@ -114,9 +121,9 @@ static int is_prefetch(struct pt_regs *regs, unsigned long error_code,
 		return 0;
 
 	while (scan_more && instr < max_instr) {
-		unsigned char opcode;
 		unsigned char instr_hi;
 		unsigned char instr_lo;
+		unsigned char opcode;
 
 		if (probe_kernel_address(instr, opcode))
 			break;
@@ -173,8 +180,9 @@ static int is_prefetch(struct pt_regs *regs, unsigned long error_code,
 	return prefetch;
 }
 
-static void force_sig_info_fault(int si_signo, int si_code,
-	unsigned long address, struct task_struct *tsk)
+static void
+force_sig_info_fault(int si_signo, int si_code, unsigned long address,
+		     struct task_struct *tsk)
 {
 	siginfo_t info;
 
@@ -182,6 +190,7 @@ static void force_sig_info_fault(int si_signo, int si_code,
 	info.si_errno	= 0;
 	info.si_code	= si_code;
 	info.si_addr	= (void __user *)address;
+
 	force_sig_info(si_signo, &info, tsk);
 }
 
@@ -189,6 +198,7 @@ static void force_sig_info_fault(int si_signo, int si_code,
 static int bad_address(void *p)
 {
 	unsigned long dummy;
+
 	return probe_kernel_address((unsigned long *)p, dummy);
 }
 #endif
@@ -200,6 +210,7 @@ static void dump_pagetable(unsigned long address)
 
 	page = read_cr3();
 	page = ((__typeof__(page) *) __va(page))[address >> PGDIR_SHIFT];
+
 #ifdef CONFIG_X86_PAE
 	printk("*pdpt = %016Lx ", page);
 	if ((page >> PAGE_SHIFT) < max_low_pfn
@@ -218,11 +229,12 @@ static void dump_pagetable(unsigned long address)
 	 * We must not directly access the pte in the highpte
 	 * case if the page table is located in highmem.
 	 * And let's rather not kmap-atomic the pte, just in case
-	 * it's allocated already.
+	 * it's allocated already:
 	 */
 	if ((page >> PAGE_SHIFT) < max_low_pfn
 	    && (page & _PAGE_PRESENT)
 	    && !(page & _PAGE_PSE)) {
+
 		page &= PAGE_MASK;
 		page = ((__typeof__(page) *) __va(page))[(address >> PAGE_SHIFT)
 							& (PTRS_PER_PTE - 1)];
@@ -239,26 +251,38 @@ static void dump_pagetable(unsigned long address)
 	pgd = (pgd_t *)read_cr3();
 
 	pgd = __va((unsigned long)pgd & PHYSICAL_PAGE_MASK);
+
 	pgd += pgd_index(address);
-	if (bad_address(pgd)) goto bad;
+	if (bad_address(pgd))
+		goto bad;
+
 	printk("PGD %lx ", pgd_val(*pgd));
-	if (!pgd_present(*pgd)) goto ret;
+
+	if (!pgd_present(*pgd))
+		goto out;
 
 	pud = pud_offset(pgd, address);
-	if (bad_address(pud)) goto bad;
+	if (bad_address(pud))
+		goto bad;
+
 	printk("PUD %lx ", pud_val(*pud));
 	if (!pud_present(*pud) || pud_large(*pud))
-		goto ret;
+		goto out;
 
 	pmd = pmd_offset(pud, address);
-	if (bad_address(pmd)) goto bad;
+	if (bad_address(pmd))
+		goto bad;
+
 	printk("PMD %lx ", pmd_val(*pmd));
-	if (!pmd_present(*pmd) || pmd_large(*pmd)) goto ret;
+	if (!pmd_present(*pmd) || pmd_large(*pmd))
+		goto out;
 
 	pte = pte_offset_kernel(pmd, address);
-	if (bad_address(pte)) goto bad;
+	if (bad_address(pte))
+		goto bad;
+
 	printk("PTE %lx", pte_val(*pte));
-ret:
+out:
 	printk("\n");
 	return;
 bad:
@@ -285,7 +309,6 @@ static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
 	 * and redundant with the set_pmd() on non-PAE. As would
 	 * set_pud.
 	 */
-
 	pud = pud_offset(pgd, address);
 	pud_k = pud_offset(pgd_k, address);
 	if (!pud_present(*pud_k))
@@ -295,11 +318,14 @@ static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
 	pmd_k = pmd_offset(pud_k, address);
 	if (!pmd_present(*pmd_k))
 		return NULL;
+
 	if (!pmd_present(*pmd)) {
 		set_pmd(pmd, *pmd_k);
 		arch_flush_lazy_mmu_mode();
-	} else
+	} else {
 		BUG_ON(pmd_page(*pmd) != pmd_page(*pmd_k));
+	}
+
 	return pmd_k;
 }
 #endif
@@ -312,29 +338,37 @@ KERN_ERR "******* Please consider a BIOS update.\n"
 KERN_ERR "******* Disabling USB legacy in the BIOS may also help.\n";
 #endif
 
-/* Workaround for K8 erratum #93 & buggy BIOS.
-   BIOS SMM functions are required to use a specific workaround
-   to avoid corruption of the 64bit RIP register on C stepping K8.
-   A lot of BIOS that didn't get tested properly miss this.
-   The OS sees this as a page fault with the upper 32bits of RIP cleared.
-   Try to work around it here.
-   Note we only handle faults in kernel here.
-   Does nothing for X86_32
+/*
+ * Workaround for K8 erratum #93 & buggy BIOS.
+ *
+ * BIOS SMM functions are required to use a specific workaround
+ * to avoid corruption of the 64bit RIP register on C stepping K8.
+ *
+ * A lot of BIOS that didn't get tested properly miss this.
+ *
+ * The OS sees this as a page fault with the upper 32bits of RIP cleared.
+ * Try to work around it here.
+ *
+ * Note we only handle faults in kernel here.
+ * Does nothing on 32-bit.
  */
 static int is_errata93(struct pt_regs *regs, unsigned long address)
 {
 #ifdef CONFIG_X86_64
-	static int warned;
+	static int once;
+
 	if (address != regs->ip)
 		return 0;
+
 	if ((address >> 32) != 0)
 		return 0;
+
 	address |= 0xffffffffUL << 32;
 	if ((address >= (u64)_stext && address <= (u64)_etext) ||
 	    (address >= MODULES_VADDR && address <= MODULES_END)) {
-		if (!warned) {
+		if (!once) {
 			printk(errata93_warning);
-			warned = 1;
+			once = 1;
 		}
 		regs->ip = address;
 		return 1;
@@ -344,16 +378,17 @@ static int is_errata93(struct pt_regs *regs, unsigned long address)
 }
 
 /*
- * Work around K8 erratum #100 K8 in compat mode occasionally jumps to illegal
- * addresses >4GB.  We catch this in the page fault handler because these
- * addresses are not reachable. Just detect this case and return.  Any code
+ * Work around K8 erratum #100 K8 in compat mode occasionally jumps
+ * to illegal addresses >4GB.
+ *
+ * We catch this in the page fault handler because these addresses
+ * are not reachable. Just detect this case and return.  Any code
  * segment in LDT is compatibility mode.
  */
 static int is_errata100(struct pt_regs *regs, unsigned long address)
 {
 #ifdef CONFIG_X86_64
-	if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) &&
-	    (address >> 32))
+	if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) && (address >> 32))
 		return 1;
 #endif
 	return 0;
@@ -363,8 +398,9 @@ static int is_f00f_bug(struct pt_regs *regs, unsigned long address)
 {
 #ifdef CONFIG_X86_F00F_BUG
 	unsigned long nr;
+
 	/*
-	 * Pentium F0 0F C7 C8 bug workaround.
+	 * Pentium F0 0F C7 C8 bug workaround:
 	 */
 	if (boot_cpu_data.f00f_bug) {
 		nr = (address - idt_descr.address) >> 3;
@@ -378,7 +414,8 @@ static int is_f00f_bug(struct pt_regs *regs, unsigned long address)
 	return 0;
 }
 
-static void show_fault_oops(struct pt_regs *regs, unsigned long error_code,
+static void
+show_fault_oops(struct pt_regs *regs, unsigned long error_code,
 		unsigned long address)
 {
 #ifdef CONFIG_X86_32
@@ -389,13 +426,15 @@ static void show_fault_oops(struct pt_regs *regs, unsigned long error_code,
 #ifdef CONFIG_X86_PAE
 	if (error_code & PF_INSTR) {
 		unsigned int level;
+
 		pte_t *pte = lookup_address(address, &level);
 
-		if (pte && pte_present(*pte) && !pte_exec(*pte))
+		if (pte && pte_present(*pte) && !pte_exec(*pte)) {
 			printk(KERN_CRIT "kernel tried to execute "
 				"NX-protected page - exploit attempt? "
 				"(uid: %d)\n", current_uid());
 		}
+	}
 #endif
 
 	printk(KERN_ALERT "BUG: unable to handle kernel ");
@@ -403,34 +442,45 @@ static void show_fault_oops(struct pt_regs *regs, unsigned long error_code,
 		printk(KERN_CONT "NULL pointer dereference");
 	else
 		printk(KERN_CONT "paging request");
+
 	printk(KERN_CONT " at %p\n", (void *) address);
 	printk(KERN_ALERT "IP:");
 	printk_address(regs->ip, 1);
+
 	dump_pagetable(address);
 }
 
 #ifdef CONFIG_X86_64
-static noinline void pgtable_bad(struct pt_regs *regs,
-			 unsigned long error_code, unsigned long address)
+static noinline void
+pgtable_bad(struct pt_regs *regs, unsigned long error_code,
+	    unsigned long address)
 {
-	unsigned long flags = oops_begin();
-	int sig = SIGKILL;
-	struct task_struct *tsk = current;
+	struct task_struct *tsk;
+	unsigned long flags;
+	int sig;
+
+	flags = oops_begin();
+	tsk = current;
+	sig = SIGKILL;
 
 	printk(KERN_ALERT "%s: Corrupted page table at address %lx\n",
 	       tsk->comm, address);
 	dump_pagetable(address);
+
 	tsk->thread.cr2		= address;
 	tsk->thread.trap_no	= 14;
 	tsk->thread.error_code	= error_code;
+
 	if (__die("Bad pagetable", regs, error_code))
 		sig = 0;
+
 	oops_end(flags, regs, sig);
 }
 #endif
 
-static noinline void no_context(struct pt_regs *regs,
-			unsigned long error_code, unsigned long address)
+static noinline void
+no_context(struct pt_regs *regs, unsigned long error_code,
+	   unsigned long address)
 {
 	struct task_struct *tsk = current;
 	unsigned long *stackend;
@@ -445,12 +495,14 @@ static noinline void no_context(struct pt_regs *regs,
 		return;
 
 	/*
-	 * X86_32
+	 * 32-bit:
+	 *
 	 *   Valid to do another page fault here, because if this fault
 	 *   had been triggered by is_prefetch fixup_exception would have
 	 *   handled it.
 	 *
-	 * X86_64
+	 * 64-bit:
+	 *
 	 *   Hall of shame of CPU/BIOS bugs.
 	 */
 	if (is_prefetch(regs, error_code, address))
@@ -461,7 +513,7 @@ static noinline void no_context(struct pt_regs *regs,
 
 	/*
 	 * Oops. The kernel tried to access some bad page. We'll have to
-	 * terminate things with extreme prejudice.
+	 * terminate things with extreme prejudice:
 	 */
 #ifdef CONFIG_X86_32
 	bust_spinlocks(1);
@@ -487,28 +539,54 @@ static noinline void no_context(struct pt_regs *regs,
 	sig = SIGKILL;
 	if (__die("Oops", regs, error_code))
 		sig = 0;
+
 	/* Executive summary in case the body of the oops scrolled away */
 	printk(KERN_EMERG "CR2: %016lx\n", address);
+
 	oops_end(flags, regs, sig);
 #endif
 }
 
-static void __bad_area_nosemaphore(struct pt_regs *regs,
-			unsigned long error_code, unsigned long address,
-			int si_code)
+/*
+ * Print out info about fatal segfaults, if the show_unhandled_signals
+ * sysctl is set:
+ */
+static inline void
+show_signal_msg(struct pt_regs *regs, unsigned long error_code,
+		unsigned long address, struct task_struct *tsk)
+{
+	if (!unhandled_signal(tsk, SIGSEGV))
+		return;
+
+	if (!printk_ratelimit())
+		return;
+
+	printk(KERN_CONT "%s%s[%d]: segfault at %lx ip %p sp %p error %lx",
+		task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
+		tsk->comm, task_pid_nr(tsk), address,
+		(void *)regs->ip, (void *)regs->sp, error_code);
+
+	print_vma_addr(KERN_CONT " in ", regs->ip);
+
+	printk(KERN_CONT "\n");
+}
+
+static void
+__bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
+		       unsigned long address, int si_code)
 {
 	struct task_struct *tsk = current;
 
 	/* User mode accesses just cause a SIGSEGV */
 	if (error_code & PF_USER) {
 		/*
-		 * It's possible to have interrupts off here.
+		 * It's possible to have interrupts off here:
 		 */
 		local_irq_enable();
 
 		/*
 		 * Valid to do another page fault here because this one came
-		 * from user space.
+		 * from user space:
 		 */
 		if (is_prefetch(regs, error_code, address))
 			return;
@@ -516,22 +594,16 @@ static void __bad_area_nosemaphore(struct pt_regs *regs,
 		if (is_errata100(regs, address))
 			return;
 
-		if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) &&
-		    printk_ratelimit()) {
-			printk(
-			"%s%s[%d]: segfault at %lx ip %p sp %p error %lx",
-			task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
-			tsk->comm, task_pid_nr(tsk), address,
-			(void *) regs->ip, (void *) regs->sp, error_code);
-			print_vma_addr(" in ", regs->ip);
-			printk("\n");
-		}
+		if (unlikely(show_unhandled_signals))
+			show_signal_msg(regs, error_code, address, tsk);
 
+		/* Kernel addresses are always protection faults: */
 		tsk->thread.cr2		= address;
-		/* Kernel addresses are always protection faults */
 		tsk->thread.error_code	= error_code | (address >= TASK_SIZE);
 		tsk->thread.trap_no	= 14;
+
 		force_sig_info_fault(SIGSEGV, si_code, address, tsk);
+
 		return;
 	}
 
@@ -541,15 +613,16 @@ static void __bad_area_nosemaphore(struct pt_regs *regs,
 	no_context(regs, error_code, address);
 }
 
-static noinline void bad_area_nosemaphore(struct pt_regs *regs,
-			unsigned long error_code, unsigned long address)
+static noinline void
+bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
+		     unsigned long address)
 {
 	__bad_area_nosemaphore(regs, error_code, address, SEGV_MAPERR);
 }
 
-static void __bad_area(struct pt_regs *regs,
-			unsigned long error_code, unsigned long address,
-			int si_code)
+static void
+__bad_area(struct pt_regs *regs, unsigned long error_code,
+	   unsigned long address, int si_code)
 {
 	struct mm_struct *mm = current->mm;
 
@@ -562,67 +635,77 @@ static void __bad_area(struct pt_regs *regs,
 	__bad_area_nosemaphore(regs, error_code, address, si_code);
 }
 
-static noinline void bad_area(struct pt_regs *regs,
-			unsigned long error_code, unsigned long address)
+static noinline void
+bad_area(struct pt_regs *regs, unsigned long error_code, unsigned long address)
 {
 	__bad_area(regs, error_code, address, SEGV_MAPERR);
 }
 
-static noinline void bad_area_access_error(struct pt_regs *regs,
-			unsigned long error_code, unsigned long address)
+static noinline void
+bad_area_access_error(struct pt_regs *regs, unsigned long error_code,
+		      unsigned long address)
 {
 	__bad_area(regs, error_code, address, SEGV_ACCERR);
 }
 
 /* TODO: fixup for "mm-invoke-oom-killer-from-page-fault.patch" */
-static void out_of_memory(struct pt_regs *regs,
-			unsigned long error_code, unsigned long address)
+static void
+out_of_memory(struct pt_regs *regs, unsigned long error_code,
+	      unsigned long address)
 {
 	/*
 	 * We ran out of memory, call the OOM killer, and return the userspace
-	 * (which will retry the fault, or kill us if we got oom-killed).
+	 * (which will retry the fault, or kill us if we got oom-killed):
 	 */
 	up_read(&current->mm->mmap_sem);
+
 	pagefault_out_of_memory();
 }
 
-static void do_sigbus(struct pt_regs *regs,
-			unsigned long error_code, unsigned long address)
+static void
+do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address)
 {
 	struct task_struct *tsk = current;
 	struct mm_struct *mm = tsk->mm;
 
 	up_read(&mm->mmap_sem);
 
-	/* Kernel mode? Handle exceptions or die */
+	/* Kernel mode? Handle exceptions or die: */
 	if (!(error_code & PF_USER))
 		no_context(regs, error_code, address);
+
 #ifdef CONFIG_X86_32
-	/* User space => ok to do another page fault */
+	/* User space => ok to do another page fault: */
 	if (is_prefetch(regs, error_code, address))
 		return;
 #endif
+
 	tsk->thread.cr2		= address;
 	tsk->thread.error_code	= error_code;
 	tsk->thread.trap_no	= 14;
+
 	force_sig_info_fault(SIGBUS, BUS_ADRERR, address, tsk);
 }
 
-static noinline void mm_fault_error(struct pt_regs *regs,
-		unsigned long error_code, unsigned long address, unsigned int fault)
+static noinline void
+mm_fault_error(struct pt_regs *regs, unsigned long error_code,
+	       unsigned long address, unsigned int fault)
 {
-	if (fault & VM_FAULT_OOM)
+	if (fault & VM_FAULT_OOM) {
 		out_of_memory(regs, error_code, address);
-	else if (fault & VM_FAULT_SIGBUS)
+	} else {
+		if (fault & VM_FAULT_SIGBUS)
 			do_sigbus(regs, error_code, address);
 		else
 			BUG();
+	}
 }
 
 static int spurious_fault_check(unsigned long error_code, pte_t *pte)
 {
 	if ((error_code & PF_WRITE) && !pte_write(*pte))
 		return 0;
+
 	if ((error_code & PF_INSTR) && !pte_exec(*pte))
 		return 0;
 
@@ -630,16 +713,19 @@ static int spurious_fault_check(unsigned long error_code, pte_t *pte)
 }
 
 /*
- * Handle a spurious fault caused by a stale TLB entry.  This allows
- * us to lazily refresh the TLB when increasing the permissions of a
- * kernel page (RO -> RW or NX -> X).  Doing it eagerly is very
- * expensive since that implies doing a full cross-processor TLB
- * flush, even if no stale TLB entries exist on other processors.
+ * Handle a spurious fault caused by a stale TLB entry.
+ *
+ * This allows us to lazily refresh the TLB when increasing the
+ * permissions of a kernel page (RO -> RW or NX -> X).  Doing it
+ * eagerly is very expensive since that implies doing a full
+ * cross-processor TLB flush, even if no stale TLB entries exist
+ * on other processors.
+ *
  * There are no security implications to leaving a stale TLB when
  * increasing the permissions on a page.
  */
-static noinline int spurious_fault(unsigned long error_code,
-				unsigned long address)
+static noinline int
+spurious_fault(unsigned long error_code, unsigned long address)
 {
 	pgd_t *pgd;
 	pud_t *pud;
@@ -678,19 +764,22 @@ static noinline int spurious_fault(unsigned long error_code,
 		return 0;
 
 	/*
-	 * Make sure we have permissions in PMD
-	 * If not, then there's a bug in the page tables.
+	 * Make sure we have permissions in PMD.
+	 * If not, then there's a bug in the page tables:
 	 */
 	ret = spurious_fault_check(error_code, (pte_t *) pmd);
 	WARN_ONCE(!ret, "PMD has incorrect permission bits\n");
+
 	return ret;
 }
 
 /*
- * X86_32
+ * 32-bit:
+ *
  *   Handle a fault on the vmalloc or module mapping area
  *
- * X86_64
+ * 64-bit:
+ *
  *   Handle a fault on the vmalloc area
  *
  * This assumes no large pages in there.
@@ -702,7 +791,7 @@ static noinline int vmalloc_fault(unsigned long address)
 	pmd_t *pmd_k;
 	pte_t *pte_k;
 
-	/* Make sure we are in vmalloc area */
+	/* Make sure we are in vmalloc area: */
 	if (!(address >= VMALLOC_START && address < VMALLOC_END))
 		return -1;
 
@@ -717,9 +806,11 @@ static noinline int vmalloc_fault(unsigned long address)
 	pmd_k = vmalloc_sync_one(__va(pgd_paddr), address);
 	if (!pmd_k)
 		return -1;
+
 	pte_k = pte_offset_kernel(pmd_k, address);
 	if (!pte_present(*pte_k))
 		return -1;
+
 	return 0;
 #else
 	pgd_t *pgd, *pgd_ref;
@@ -727,68 +818,83 @@ static noinline int vmalloc_fault(unsigned long address)
 	pmd_t *pmd, *pmd_ref;
 	pte_t *pte, *pte_ref;
 
-	/* Make sure we are in vmalloc area */
+	/* Make sure we are in vmalloc area: */
 	if (!(address >= VMALLOC_START && address < VMALLOC_END))
 		return -1;
 
-	/* Copy kernel mappings over when needed. This can also
-	   happen within a race in page table update. In the later
-	   case just flush. */
-
+	/*
+	 * Copy kernel mappings over when needed. This can also
+	 * happen within a race in page table update. In the later
+	 * case just flush:
+	 */
 	pgd = pgd_offset(current->active_mm, address);
 	pgd_ref = pgd_offset_k(address);
 	if (pgd_none(*pgd_ref))
 		return -1;
+
 	if (pgd_none(*pgd))
 		set_pgd(pgd, *pgd_ref);
 	else
 		BUG_ON(pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_ref));
 
-	/* Below here mismatches are bugs because these lower tables
-	   are shared */
+	/*
+	 * Below here mismatches are bugs because these lower tables
+	 * are shared:
+	 */
 
 	pud = pud_offset(pgd, address);
 	pud_ref = pud_offset(pgd_ref, address);
 	if (pud_none(*pud_ref))
 		return -1;
+
 	if (pud_none(*pud) || pud_page_vaddr(*pud) != pud_page_vaddr(*pud_ref))
 		BUG();
+
 	pmd = pmd_offset(pud, address);
 	pmd_ref = pmd_offset(pud_ref, address);
 	if (pmd_none(*pmd_ref))
 		return -1;
+
 	if (pmd_none(*pmd) || pmd_page(*pmd) != pmd_page(*pmd_ref))
 		BUG();
+
 	pte_ref = pte_offset_kernel(pmd_ref, address);
 	if (!pte_present(*pte_ref))
 		return -1;
+
 	pte = pte_offset_kernel(pmd, address);
-	/* Don't use pte_page here, because the mappings can point
-	   outside mem_map, and the NUMA hash lookup cannot handle
-	   that. */
+
+	/*
+	 * Don't use pte_page here, because the mappings can point
+	 * outside mem_map, and the NUMA hash lookup cannot handle
+	 * that:
+	 */
 	if (!pte_present(*pte) || pte_pfn(*pte) != pte_pfn(*pte_ref))
 		BUG();
+
 	return 0;
 #endif
 }
 
 int show_unhandled_signals = 1;
 
-static inline int access_error(unsigned long error_code, int write,
-				struct vm_area_struct *vma)
+static inline int
+access_error(unsigned long error_code, int write, struct vm_area_struct *vma)
 {
 	if (write) {
-		/* write, present and write, not present */
+		/* write, present and write, not present: */
 		if (unlikely(!(vma->vm_flags & VM_WRITE)))
 			return 1;
-	} else if (unlikely(error_code & PF_PROT)) {
-		/* read, present */
+		return 0;
+	}
+
+	/* read, present: */
+	if (unlikely(error_code & PF_PROT))
 		return 1;
-	} else {
-		/* read, not present */
+
+	/* read, not present: */
 	if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))))
 		return 1;
-	}
 
 	return 0;
 }
@@ -797,9 +903,9 @@ static int fault_in_kernel_space(unsigned long address)
 {
 #ifdef CONFIG_X86_32
 	return address >= TASK_SIZE;
-#else /* !CONFIG_X86_32 */
+#else
 	return address >= TASK_SIZE64;
-#endif /* CONFIG_X86_32 */
+#endif
 }
 
 /*
@@ -812,18 +918,19 @@ asmlinkage
 #endif
 void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code)
 {
-	unsigned long address;
+	struct vm_area_struct *vma;
 	struct task_struct *tsk;
+	unsigned long address;
 	struct mm_struct *mm;
-	struct vm_area_struct *vma;
 	int write;
 	int fault;
 
 	tsk = current;
 	mm = tsk->mm;
+
 	prefetchw(&mm->mmap_sem);
 
-	/* get the address */
+	/* Get the faulting address: */
 	address = read_cr2();
 
 	if (unlikely(kmmio_fault(regs, address)))
@@ -847,22 +954,23 @@ void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code)
 		    vmalloc_fault(address) >= 0)
 			return;
 
-		/* Can handle a stale RO->RW TLB */
+		/* Can handle a stale RO->RW TLB: */
 		if (spurious_fault(error_code, address))
 			return;
 
-		/* kprobes don't want to hook the spurious faults. */
+		/* kprobes don't want to hook the spurious faults: */
 		if (notify_page_fault(regs))
 			return;
 		/*
 		 * Don't take the mm semaphore here. If we fixup a prefetch
-		 * fault we could otherwise deadlock.
+		 * fault we could otherwise deadlock:
 		 */
 		bad_area_nosemaphore(regs, error_code, address);
+
 		return;
 	}
 
-	/* kprobes don't want to hook the spurious faults. */
+	/* kprobes don't want to hook the spurious faults: */
 	if (unlikely(notify_page_fault(regs)))
 		return;
 	/*
@@ -870,13 +978,15 @@ void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code)
 	 * vmalloc fault has been handled.
 	 *
 	 * User-mode registers count as a user access even for any
-	 * potential system fault or CPU buglet.
+	 * potential system fault or CPU buglet:
 	 */
 	if (user_mode_vm(regs)) {
 		local_irq_enable();
 		error_code |= PF_USER;
-	} else if (regs->flags & X86_EFLAGS_IF)
+	} else {
+		if (regs->flags & X86_EFLAGS_IF)
 			local_irq_enable();
+	}
 
 #ifdef CONFIG_X86_64
 	if (unlikely(error_code & PF_RSVD))
@@ -884,8 +994,8 @@ void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code)
 #endif
 
 	/*
-	 * If we're in an interrupt, have no user context or are running in an
-	 * atomic region then we must not take the fault.
+	 * If we're in an interrupt, have no user context or are running
+	 * in an atomic region then we must not take the fault:
 	 */
 	if (unlikely(in_atomic() || !mm)) {
 		bad_area_nosemaphore(regs, error_code, address);
@@ -894,19 +1004,19 @@ void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code)
 
 	/*
 	 * When running in the kernel we expect faults to occur only to
-	 * addresses in user space.  All other faults represent errors in the
-	 * kernel and should generate an OOPS.  Unfortunately, in the case of an
-	 * erroneous fault occurring in a code path which already holds mmap_sem
-	 * we will deadlock attempting to validate the fault against the
-	 * address space.  Luckily the kernel only validly references user
-	 * space from well defined areas of code, which are listed in the
-	 * exceptions table.
+	 * addresses in user space.  All other faults represent errors in
+	 * the kernel and should generate an OOPS.  Unfortunately, in the
+	 * case of an erroneous fault occurring in a code path which already
+	 * holds mmap_sem we will deadlock attempting to validate the fault
+	 * against the address space.  Luckily the kernel only validly
+	 * references user space from well defined areas of code, which are
+	 * listed in the exceptions table.
 	 *
 	 * As the vast majority of faults will be valid we will only perform
-	 * the source reference check when there is a possibility of a deadlock.
-	 * Attempt to lock the address space, if we cannot we then validate the
-	 * source.  If this is invalid we can skip the address space check,
-	 * thus avoiding the deadlock.
+	 * the source reference check when there is a possibility of a
+	 * deadlock. Attempt to lock the address space, if we cannot we then
+	 * validate the source. If this is invalid we can skip the address
+	 * space check, thus avoiding the deadlock:
 	 */
 	if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
 		if ((error_code & PF_USER) == 0 &&
@@ -917,8 +1027,9 @@ void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code)
 		down_read(&mm->mmap_sem);
 	} else {
 		/*
-		 * The above down_read_trylock() might have succeeded in which
-		 * case we'll have missed the might_sleep() from down_read().
+		 * The above down_read_trylock() might have succeeded in
+		 * which case we'll have missed the might_sleep() from
+		 * down_read():
 		 */
 		might_sleep();
 	}
@@ -938,7 +1049,7 @@ void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code)
 		/*
 		 * Accessing the stack below %sp is always a bug.
 		 * The large cushion allows instructions like enter
-		 * and pusha to work.  ("enter $65535,$31" pushes
+		 * and pusha to work. ("enter $65535, $31" pushes
 		 * 32 pointers and then decrements %sp by 65535.)
 		 */
 		if (unlikely(address + 65536 + 32 * sizeof(unsigned long) < regs->sp)) {
@@ -957,6 +1068,7 @@ void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code)
 	 */
 good_area:
 	write = error_code & PF_WRITE;
+
 	if (unlikely(access_error(error_code, write, vma))) {
 		bad_area_access_error(regs, error_code, address);
 		return;
@@ -965,13 +1077,15 @@ void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code)
 	/*
 	 * If for any reason at all we couldn't handle the fault,
 	 * make sure we exit gracefully rather than endlessly redo
-	 * the fault.
+	 * the fault:
 	 */
 	fault = handle_mm_fault(mm, vma, address, write);
+
 	if (unlikely(fault & VM_FAULT_ERROR)) {
 		mm_fault_error(regs, error_code, address, fault);
 		return;
 	}
+
 	if (fault & VM_FAULT_MAJOR)
 		tsk->maj_flt++;
 	else
@@ -1004,13 +1118,13 @@ void vmalloc_sync_all(void)
 	for (address = VMALLOC_START & PMD_MASK;
 	     address >= TASK_SIZE && address < FIXADDR_TOP;
 	     address += PMD_SIZE) {
+
 		unsigned long flags;
 		struct page *page;
 
 		spin_lock_irqsave(&pgd_lock, flags);
 		list_for_each_entry(page, &pgd_list, lru) {
-			if (!vmalloc_sync_one(page_address(page),
-					      address))
+			if (!vmalloc_sync_one(page_address(page), address))
 				break;
 		}
 		spin_unlock_irqrestore(&pgd_lock, flags);
@@ -1018,12 +1132,14 @@ void vmalloc_sync_all(void)
 #else /* CONFIG_X86_64 */
 	for (address = VMALLOC_START & PGDIR_MASK; address <= VMALLOC_END;
 	     address += PGDIR_SIZE) {
+
 		const pgd_t *pgd_ref = pgd_offset_k(address);
 		unsigned long flags;
 		struct page *page;
 
 		if (pgd_none(*pgd_ref))
 			continue;
+
 		spin_lock_irqsave(&pgd_lock, flags);
 		list_for_each_entry(page, &pgd_list, lru) {
 			pgd_t *pgd;