x86: mm: introduce helper function in fault.c

[linux-2.6/verdex.git] / arch / x86 / mm / fault.c

/*
 *  Copyright (C) 1995  Linus Torvalds
 *  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/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/kdebug.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/proto.h>
#include <asm-generic/sections.h>
#include <asm/traps.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
 */
#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)

static inline int kmmio_fault(struct pt_regs *regs, unsigned long addr)
{
#ifdef CONFIG_MMIOTRACE
        if (unlikely(is_kmmio_active()))
                if (kmmio_handler(regs, addr) == 1)
                        return -1;
#endif
        return 0;
}

static inline int notify_page_fault(struct pt_regs *regs)
{
#ifdef CONFIG_KPROBES
        int ret = 0;

        /* kprobe_running() needs smp_processor_id() */
        if (!user_mode_vm(regs)) {
                preempt_disable();
                if (kprobe_running() && kprobe_fault_handler(regs, 14))
                        ret = 1;
                preempt_enable();
        }

        return ret;
#else
        return 0;
#endif
}

/*
 * X86_32
 * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch.
 * Check that here and ignore it.
 *
 * X86_64
 * Sometimes the CPU reports invalid exceptions on prefetch.
 * Check that here and ignore it.
 *
 * Opcode checker based on code by Richard Brunner
 */
static int is_prefetch(struct pt_regs *regs, unsigned long error_code,
                        unsigned long addr)
{
        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
         * do not ignore the fault:
         */
        if (error_code & PF_INSTR)
                return 0;

        instr = (unsigned char *)convert_ip_to_linear(current, regs);
        max_instr = instr + 15;

        if (user_mode(regs) && instr >= (unsigned char *)TASK_SIZE)
                return 0;

        while (scan_more && instr < max_instr) {
                unsigned char opcode;
                unsigned char instr_hi;
                unsigned char instr_lo;

                if (probe_kernel_address(instr, opcode))
                        break;

                instr_hi = opcode & 0xf0;
                instr_lo = opcode & 0x0f;
                instr++;

                switch (instr_hi) {
                case 0x20:
                case 0x30:
                        /*
                         * Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes.
                         * In X86_64 long mode, the CPU will signal invalid
                         * opcode if some of these prefixes are present so
                         * X86_64 will never get here anyway
                         */
                        scan_more = ((instr_lo & 7) == 0x6);
                        break;
#ifdef CONFIG_X86_64
                case 0x40:
                        /*
                         * In AMD64 long mode 0x40..0x4F are valid REX prefixes
                         * Need to figure out under what instruction mode the
                         * instruction was issued. Could check the LDT for lm,
                         * but for now it's good enough to assume that long
                         * mode only uses well known segments or kernel.
                         */
                        scan_more = (!user_mode(regs)) || (regs->cs == __USER_CS);
                        break;
#endif
                case 0x60:
                        /* 0x64 thru 0x67 are valid prefixes in all modes. */
                        scan_more = (instr_lo & 0xC) == 0x4;
                        break;
                case 0xF0:
                        /* 0xF0, 0xF2, 0xF3 are valid prefixes in all modes. */
                        scan_more = !instr_lo || (instr_lo>>1) == 1;
                        break;
                case 0x00:
                        /* Prefetch instruction is 0x0F0D or 0x0F18 */
                        scan_more = 0;

                        if (probe_kernel_address(instr, opcode))
                                break;
                        prefetch = (instr_lo == 0xF) &&
                                (opcode == 0x0D || opcode == 0x18);
                        break;
                default:
                        scan_more = 0;
                        break;
                }
        }
        return prefetch;
}

static void force_sig_info_fault(int si_signo, int si_code,
        unsigned long address, struct task_struct *tsk)
{
        siginfo_t info;

        info.si_signo = si_signo;
        info.si_errno = 0;
        info.si_code = si_code;
        info.si_addr = (void __user *)address;
        force_sig_info(si_signo, &info, tsk);
}

#ifdef CONFIG_X86_64
static int bad_address(void *p)
{
        unsigned long dummy;
        return probe_kernel_address((unsigned long *)p, dummy);
}
#endif

static void dump_pagetable(unsigned long address)
{
#ifdef CONFIG_X86_32
        __typeof__(pte_val(__pte(0))) page;

        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
            && page & _PAGE_PRESENT) {
                page &= PAGE_MASK;
                page = ((__typeof__(page) *) __va(page))[(address >> PMD_SHIFT)
                                                         & (PTRS_PER_PMD - 1)];
                printk(KERN_CONT "*pde = %016Lx ", page);
                page &= ~_PAGE_NX;
        }
#else
        printk("*pde = %08lx ", page);
#endif

        /*
         * 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.
         */
        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)];
                printk("*pte = %0*Lx ", sizeof(page)*2, (u64)page);
        }

        printk("\n");
#else /* CONFIG_X86_64 */
        pgd_t *pgd;
        pud_t *pud;
        pmd_t *pmd;
        pte_t *pte;

        pgd = (pgd_t *)read_cr3();

        pgd = __va((unsigned long)pgd & PHYSICAL_PAGE_MASK);
        pgd += pgd_index(address);
        if (bad_address(pgd)) goto bad;
        printk("PGD %lx ", pgd_val(*pgd));
        if (!pgd_present(*pgd)) goto ret;

        pud = pud_offset(pgd, address);
        if (bad_address(pud)) goto bad;
        printk("PUD %lx ", pud_val(*pud));
        if (!pud_present(*pud) || pud_large(*pud))
                goto ret;

        pmd = pmd_offset(pud, address);
        if (bad_address(pmd)) goto bad;
        printk("PMD %lx ", pmd_val(*pmd));
        if (!pmd_present(*pmd) || pmd_large(*pmd)) goto ret;

        pte = pte_offset_kernel(pmd, address);
        if (bad_address(pte)) goto bad;
        printk("PTE %lx", pte_val(*pte));
ret:
        printk("\n");
        return;
bad:
        printk("BAD\n");
#endif
}

#ifdef CONFIG_X86_32
static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
{
        unsigned index = pgd_index(address);
        pgd_t *pgd_k;
        pud_t *pud, *pud_k;
        pmd_t *pmd, *pmd_k;

        pgd += index;
        pgd_k = init_mm.pgd + index;

        if (!pgd_present(*pgd_k))
                return NULL;

        /*
         * set_pgd(pgd, *pgd_k); here would be useless on PAE
         * 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))
                return NULL;

        pmd = pmd_offset(pud, 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
                BUG_ON(pmd_page(*pmd) != pmd_page(*pmd_k));
        return pmd_k;
}
#endif

#ifdef CONFIG_X86_64
static const char errata93_warning[] =
KERN_ERR "******* Your BIOS seems to not contain a fix for K8 errata #93\n"
KERN_ERR "******* Working around it, but it may cause SEGVs or burn power.\n"
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
 */
static int is_errata93(struct pt_regs *regs, unsigned long address)
{
#ifdef CONFIG_X86_64
        static int warned;
        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) {
                        printk(errata93_warning);
                        warned = 1;
                }
                regs->ip = address;
                return 1;
        }
#endif
        return 0;
}

/*
 * 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))
                return 1;
#endif
        return 0;
}

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.
         */
        if (boot_cpu_data.f00f_bug) {
                nr = (address - idt_descr.address) >> 3;

                if (nr == 6) {
                        do_invalid_op(regs, 0);
                        return 1;
                }
        }
#endif
        return 0;
}

static void show_fault_oops(struct pt_regs *regs, unsigned long error_code,
                            unsigned long address)
{
#ifdef CONFIG_X86_32
        if (!oops_may_print())
                return;
#endif

#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))
                        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 ");
        if (address < PAGE_SIZE)
                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)
{
        unsigned long flags = oops_begin();
        int sig = SIGKILL;
        struct task_struct *tsk = current;

        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)
{
        struct task_struct *tsk = current;
#ifdef CONFIG_X86_64
        unsigned long flags;
        int sig;
#endif

        /* Are we prepared to handle this kernel fault?  */
        if (fixup_exception(regs))
                return;

        /*
         * X86_32
         * 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
         * Hall of shame of CPU/BIOS bugs.
         */
        if (is_prefetch(regs, error_code, address))
                return;

        if (is_errata93(regs, address))
                return;

        /*
         * Oops. The kernel tried to access some bad page. We'll have to
         * terminate things with extreme prejudice.
         */
#ifdef CONFIG_X86_32
        bust_spinlocks(1);
#else
        flags = oops_begin();
#endif

        show_fault_oops(regs, error_code, address);

        tsk->thread.cr2 = address;
        tsk->thread.trap_no = 14;
        tsk->thread.error_code = error_code;

#ifdef CONFIG_X86_32
        die("Oops", regs, error_code);
        bust_spinlocks(0);
        do_exit(SIGKILL);
#else
        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)
{
        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.
                 */
                local_irq_enable();

                /*
                 * Valid to do another page fault here because this one came
                 * from user space.
                 */
                if (is_prefetch(regs, error_code, address))
                        return;

                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");
                }

                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;
        }

        if (is_f00f_bug(regs, address))
                return;

        no_context(regs, error_code, 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)
{
        struct mm_struct *mm = current->mm;

        /*
         * Something tried to access memory that isn't in our memory map..
         * Fix it, but check if it's kernel or user first..
         */
        up_read(&mm->mmap_sem);

        __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)
{
        __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)
{
        __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)
{
        /*
         * 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).
         */
        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)
{
        struct task_struct *tsk = current;
        struct mm_struct *mm = tsk->mm;

        up_read(&mm->mmap_sem);

        /* 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 */
        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)
{
        if (fault & VM_FAULT_OOM)
                out_of_memory(regs, error_code, address);
        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;

        return 1;
}

/*
 * 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)
{
        pgd_t *pgd;
        pud_t *pud;
        pmd_t *pmd;
        pte_t *pte;

        /* Reserved-bit violation or user access to kernel space? */
        if (error_code & (PF_USER | PF_RSVD))
                return 0;

        pgd = init_mm.pgd + pgd_index(address);
        if (!pgd_present(*pgd))
                return 0;

        pud = pud_offset(pgd, address);
        if (!pud_present(*pud))
                return 0;

        if (pud_large(*pud))
                return spurious_fault_check(error_code, (pte_t *) pud);

        pmd = pmd_offset(pud, address);
        if (!pmd_present(*pmd))
                return 0;

        if (pmd_large(*pmd))
                return spurious_fault_check(error_code, (pte_t *) pmd);

        pte = pte_offset_kernel(pmd, address);
        if (!pte_present(*pte))
                return 0;

        return spurious_fault_check(error_code, pte);
}

/*
 * X86_32
 * Handle a fault on the vmalloc or module mapping area
 *
 * X86_64
 * Handle a fault on the vmalloc area
 *
 * This assumes no large pages in there.
 */
static noinline int vmalloc_fault(unsigned long address)
{
#ifdef CONFIG_X86_32
        unsigned long pgd_paddr;
        pmd_t *pmd_k;
        pte_t *pte_k;

        /* Make sure we are in vmalloc area */
        if (!(address >= VMALLOC_START && address < VMALLOC_END))
                return -1;

        /*
         * Synchronize this task's top level page-table
         * with the 'reference' page table.
         *
         * Do _not_ use "current" here. We might be inside
         * an interrupt in the middle of a task switch..
         */
        pgd_paddr = read_cr3();
        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;
        pud_t *pud, *pud_ref;
        pmd_t *pmd, *pmd_ref;
        pte_t *pte, *pte_ref;

        /* 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. */

        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 */

        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. */
        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)
{
        if (write) {
                /* 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 1;
        } else {
                /* read, not present */
                if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))))
                        return 1;
        }

        return 0;
}

static int fault_in_kernel_space(unsigned long address)
{
#ifdef CONFIG_X86_32
        return address >= TASK_SIZE;
#else /* !CONFIG_X86_32 */
        return address >= TASK_SIZE64;
#endif /* CONFIG_X86_32 */
}

/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to one of the appropriate
 * routines.
 */
#ifdef CONFIG_X86_64
asmlinkage
#endif
void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code)
{
        unsigned long address;
        struct task_struct *tsk;
        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 */
        address = read_cr2();

        if (unlikely(notify_page_fault(regs)))
                return;
        if (unlikely(kmmio_fault(regs, address)))
                return;

        /*
         * We fault-in kernel-space virtual memory on-demand. The
         * 'reference' page table is init_mm.pgd.
         *
         * NOTE! We MUST NOT take any locks for this case. We may
         * be in an interrupt or a critical region, and should
         * only copy the information from the master page table,
         * nothing more.
         *
         * This verifies that the fault happens in kernel space
         * (error_code & 4) == 0, and that the fault was not a
         * protection error (error_code & 9) == 0.
         */
        if (unlikely(fault_in_kernel_space(address))) {
                if (!(error_code & (PF_RSVD|PF_USER|PF_PROT)) &&
                    vmalloc_fault(address) >= 0)
                        return;

                /* Can handle a stale RO->RW TLB */
                if (spurious_fault(error_code, address))
                        return;

                /*
                 * Don't take the mm semaphore here. If we fixup a prefetch
                 * fault we could otherwise deadlock.
                 */
                bad_area_nosemaphore(regs, error_code, address);
                return;
        }

        /*
         * It's safe to allow irq's after cr2 has been saved and the
         * vmalloc fault has been handled.
         *
         * User-mode registers count as a user access even for any
         * 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)
                local_irq_enable();

#ifdef CONFIG_X86_64
        if (unlikely(error_code & PF_RSVD))
                pgtable_bad(regs, error_code, address);
#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 (unlikely(in_atomic() || !mm)) {
                bad_area_nosemaphore(regs, error_code, address);
                return;
        }

        /*
         * 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.
         *
         * 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.
         */
        if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
                if ((error_code & PF_USER) == 0 &&
                    !search_exception_tables(regs->ip)) {
                        bad_area_nosemaphore(regs, error_code, address);
                        return;
                }
                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().
                 */
                might_sleep();
        }

        vma = find_vma(mm, address);
        if (unlikely(!vma)) {
                bad_area(regs, error_code, address);
                return;
        }
        if (likely(vma->vm_start <= address))
                goto good_area;
        if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) {
                bad_area(regs, error_code, address);
                return;
        }
        if (error_code & PF_USER) {
                /*
                 * Accessing the stack below %sp is always a bug.
                 * The large cushion allows instructions like enter
                 * 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)) {
                        bad_area(regs, error_code, address);
                        return;
                }
        }
        if (unlikely(expand_stack(vma, address))) {
                bad_area(regs, error_code, address);
                return;
        }

        /*
         * Ok, we have a good vm_area for this memory access, so
         * we can handle it..
         */
good_area:
        write = error_code & PF_WRITE;
        if (unlikely(access_error(error_code, write, vma))) {
                bad_area_access_error(regs, error_code, address);
                return;
        }

        /*
         * If for any reason at all we couldn't handle the fault,
         * make sure we exit gracefully rather than endlessly redo
         * 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
                tsk->min_flt++;

#ifdef CONFIG_X86_32
        /*
         * Did it hit the DOS screen memory VA from vm86 mode?
         */
        if (v8086_mode(regs)) {
                unsigned long bit = (address - 0xA0000) >> PAGE_SHIFT;
                if (bit < 32)
                        tsk->thread.screen_bitmap |= 1 << bit;
        }
#endif
        up_read(&mm->mmap_sem);
}

DEFINE_SPINLOCK(pgd_lock);
LIST_HEAD(pgd_list);

void vmalloc_sync_all(void)
{
        unsigned long address;

#ifdef CONFIG_X86_32
        if (SHARED_KERNEL_PMD)
                return;

        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))
                                break;
                }
                spin_unlock_irqrestore(&pgd_lock, flags);
        }
#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;
                        pgd = (pgd_t *)page_address(page) + pgd_index(address);
                        if (pgd_none(*pgd))
                                set_pgd(pgd, *pgd_ref);
                        else
                                BUG_ON(pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_ref));
                }
                spin_unlock_irqrestore(&pgd_lock, flags);
        }
#endif
}