source: trunk/packages/xen-3.1/xen-3.1/linux-2.6-xen-sparse/arch/x86_64/mm/fault-xen.c @ 34

/*
 *  linux/arch/x86-64/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/mman.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/smp_lock.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/module.h>
#include <linux/kprobes.h>

#include <asm/system.h>
#include <asm/uaccess.h>
#include <asm/pgalloc.h>
#include <asm/smp.h>
#include <asm/tlbflush.h>
#include <asm/proto.h>
#include <asm/kdebug.h>
#include <asm-generic/sections.h>

/* Page fault error code bits */
#define PF_PROT (1<<0)          /* or no page found */
#define PF_WRITE        (1<<1)
#define PF_USER (1<<2)
#define PF_RSVD (1<<3)
#define PF_INSTR        (1<<4)

#ifdef CONFIG_KPROBES
ATOMIC_NOTIFIER_HEAD(notify_page_fault_chain);

/* Hook to register for page fault notifications */
int register_page_fault_notifier(struct notifier_block *nb)
{
        vmalloc_sync_all();
        return atomic_notifier_chain_register(&notify_page_fault_chain, nb);
}

int unregister_page_fault_notifier(struct notifier_block *nb)
{
        return atomic_notifier_chain_unregister(&notify_page_fault_chain, nb);
}

static inline int notify_page_fault(enum die_val val, const char *str,
                        struct pt_regs *regs, long err, int trap, int sig)
{
        struct die_args args = {
                .regs = regs,
                .str = str,
                .err = err,
                .trapnr = trap,
                .signr = sig
        };
        return atomic_notifier_call_chain(&notify_page_fault_chain, val, &args);
}
#else
static inline int notify_page_fault(enum die_val val, const char *str,
                        struct pt_regs *regs, long err, int trap, int sig)
{
        return NOTIFY_DONE;
}
#endif

void bust_spinlocks(int yes)
{
        int loglevel_save = console_loglevel;
        if (yes) {
                oops_in_progress = 1;
        } else {
#ifdef CONFIG_VT
                unblank_screen();
#endif
                oops_in_progress = 0;
                /*
                 * OK, the message is on the console.  Now we call printk()
                 * without oops_in_progress set so that printk will give klogd
                 * a poke.  Hold onto your hats...
                 */
                console_loglevel = 15;          /* NMI oopser may have shut the console up */
                printk(" ");
                console_loglevel = loglevel_save;
        }
}

/* Sometimes the CPU reports invalid exceptions on prefetch.
   Check that here and ignore.
   Opcode checker based on code by Richard Brunner */
static noinline int is_prefetch(struct pt_regs *regs, unsigned long addr,
                                unsigned long error_code)
{ 
        unsigned char *instr;
        int scan_more = 1;
        int prefetch = 0; 
        unsigned char *max_instr;

        /* If it was a exec fault ignore */
        if (error_code & PF_INSTR)
                return 0;
        
        instr = (unsigned char *)convert_rip_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 (__get_user(opcode, instr))
                        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 long mode, the CPU will signal
                           invalid opcode if some of these prefixes are
                           present so we will never get here anyway */
                        scan_more = ((instr_lo & 7) == 0x6);
                        break;
                        
                case 0x40:
                        /* In AMD64 long mode, 0x40 to 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;
                        
                case 0x60:
                        /* 0x64 thru 0x67 are valid prefixes in all modes. */
                        scan_more = (instr_lo & 0xC) == 0x4;
                        break;          
                case 0xF0:
                        /* 0xF0, 0xF2, and 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 (__get_user(opcode, instr)) 
                                break;
                        prefetch = (instr_lo == 0xF) &&
                                (opcode == 0x0D || opcode == 0x18);
                        break;                  
                default:
                        scan_more = 0;
                        break;
                } 
        }
        return prefetch;
}

static int bad_address(void *p) 
{ 
        unsigned long dummy;
        return __get_user(dummy, (unsigned long *)p);
} 

void dump_pagetable(unsigned long address)
{
        pgd_t *pgd;
        pud_t *pud;
        pmd_t *pmd;
        pte_t *pte;

        pgd = __va(read_cr3() & 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)) goto ret;

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

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";

/* 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. */

static int is_errata93(struct pt_regs *regs, unsigned long address) 
{
        static int warned;
        if (address != regs->rip)
                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->rip = address;
                return 1;
        }
        return 0;
} 

int unhandled_signal(struct task_struct *tsk, int sig)
{
        if (tsk->pid == 1)
                return 1;
        if (tsk->ptrace & PT_PTRACED)
                return 0;
        return (tsk->sighand->action[sig-1].sa.sa_handler == SIG_IGN) ||
                (tsk->sighand->action[sig-1].sa.sa_handler == SIG_DFL);
}

static noinline void pgtable_bad(unsigned long address, struct pt_regs *regs,
                                 unsigned long error_code)
{
        unsigned long flags = oops_begin();
        struct task_struct *tsk;

        printk(KERN_ALERT "%s: Corrupted page table at address %lx\n",
               current->comm, address);
        dump_pagetable(address);
        tsk = current;
        tsk->thread.cr2 = address;
        tsk->thread.trap_no = 14;
        tsk->thread.error_code = error_code;
        __die("Bad pagetable", regs, error_code);
        oops_end(flags);
        do_exit(SIGKILL);
}

/*
 * Handle a fault on the vmalloc area
 *
 * This assumes no large pages in there.
 */
static int vmalloc_fault(unsigned long address)
{
        pgd_t *pgd, *pgd_ref;
        pud_t *pud, *pud_ref;
        pmd_t *pmd, *pmd_ref;
        pte_t *pte, *pte_ref;

        /* Copy kernel mappings over when needed. This can also
           happen within a race in page table update. In the later
           case just flush. */

        /* On Xen the line below does not always work. Needs investigating! */
        /*pgd = pgd_offset(current->mm ?: &init_mm, address);*/
        pgd = __va(read_cr3() & PHYSICAL_PAGE_MASK);
        pgd += pgd_index(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(*pgd) != pgd_page(*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(*pud) != pud_page(*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;
}

int page_fault_trace = 0;
int exception_trace = 1;


#define MEM_VERBOSE 1

#ifdef MEM_VERBOSE
#define MEM_LOG(_f, _a...)                      \
        printk("fault.c:[%d]-> " _f "\n",       \
        __LINE__ , ## _a )
#else
#define MEM_LOG(_f, _a...) ((void)0)
#endif

static int spurious_fault(struct pt_regs *regs,
                          unsigned long address,
                          unsigned long error_code)
{
        pgd_t *pgd;
        pud_t *pud;
        pmd_t *pmd;
        pte_t *pte;

#ifdef CONFIG_XEN
        /* Faults in hypervisor area are never spurious. */
        if ((address >= HYPERVISOR_VIRT_START) &&
            (address < HYPERVISOR_VIRT_END))
                return 0;
#endif

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

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

        pte = pte_offset_kernel(pmd, address);
        if (!pte_present(*pte))
                return 0;
        if ((error_code & PF_WRITE) && !pte_write(*pte))
                return 0;
        if ((error_code & PF_INSTR) && (pte_val(*pte) & _PAGE_NX))
                return 0;

        return 1;
}

/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to one of the appropriate
 * routines.
 */
asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
                                        unsigned long error_code)
{
        struct task_struct *tsk;
        struct mm_struct *mm;
        struct vm_area_struct * vma;
        unsigned long address;
        const struct exception_table_entry *fixup;
        int write;
        unsigned long flags;
        siginfo_t info;

        if (!user_mode(regs))
                error_code &= ~PF_USER; /* means kernel */

        tsk = current;
        mm = tsk->mm;
        prefetchw(&mm->mmap_sem);

        /* get the address */
        address = current_vcpu_info()->arch.cr2;

        info.si_code = SEGV_MAPERR;


        /*
         * 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(address >= TASK_SIZE64)) {
                /*
                 * Don't check for the module range here: its PML4
                 * is always initialized because it's shared with the main
                 * kernel text. Only vmalloc may need PML4 syncups.
                 */
                if (!(error_code & (PF_RSVD|PF_USER|PF_PROT)) &&
                      ((address >= VMALLOC_START && address < VMALLOC_END))) {
                        if (vmalloc_fault(address) >= 0)
                                return;
                }
                /* Can take a spurious fault if mapping changes R/O -> R/W. */
                if (spurious_fault(regs, address, error_code))
                        return;
                if (notify_page_fault(DIE_PAGE_FAULT, "page fault", regs, error_code, 14,
                                                SIGSEGV) == NOTIFY_STOP)
                        return;
                /*
                 * Don't take the mm semaphore here. If we fixup a prefetch
                 * fault we could otherwise deadlock.
                 */
                goto bad_area_nosemaphore;
        }

        if (notify_page_fault(DIE_PAGE_FAULT, "page fault", regs, error_code, 14,
                                        SIGSEGV) == NOTIFY_STOP)
                return;

        if (likely(regs->eflags & X86_EFLAGS_IF))
                local_irq_enable();

        if (unlikely(page_fault_trace))
                printk("pagefault rip:%lx rsp:%lx cs:%lu ss:%lu address %lx error %lx\n",
                       regs->rip,regs->rsp,regs->cs,regs->ss,address,error_code); 

        if (unlikely(error_code & PF_RSVD))
                pgtable_bad(address, regs, error_code);

        /*
         * If we're in an interrupt or have no user
         * context, we must not take the fault..
         */
        if (unlikely(in_atomic() || !mm))
                goto bad_area_nosemaphore;

 again:
        /* 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.  Unfortunatly, 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 possibilty 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 (!down_read_trylock(&mm->mmap_sem)) {
                if ((error_code & PF_USER) == 0 &&
                    !search_exception_tables(regs->rip))
                        goto bad_area_nosemaphore;
                down_read(&mm->mmap_sem);
        }

        vma = find_vma(mm, address);
        if (!vma)
                goto bad_area;
        if (likely(vma->vm_start <= address))
                goto good_area;
        if (!(vma->vm_flags & VM_GROWSDOWN))
                goto bad_area;
        if (error_code & 4) {
                /* Allow userspace just enough access below the stack pointer
                 * to let the 'enter' instruction work.
                 */
                if (address + 65536 + 32 * sizeof(unsigned long) < regs->rsp)
                        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:
        info.si_code = SEGV_ACCERR;
        write = 0;
        switch (error_code & (PF_PROT|PF_WRITE)) {
                default:        /* 3: write, present */
                        /* fall through */
                case PF_WRITE:          /* write, not present */
                        if (!(vma->vm_flags & VM_WRITE))
                                goto bad_area;
                        write++;
                        break;
                case PF_PROT:           /* read, present */
                        goto bad_area;
                case 0:                 /* read, not present */
                        if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
                                goto bad_area;
        }

        /*
         * If for any reason at all we couldn't handle the fault,
         * make sure we exit gracefully rather than endlessly redo
         * the fault.
         */
        switch (handle_mm_fault(mm, vma, address, write)) {
        case VM_FAULT_MINOR:
                tsk->min_flt++;
                break;
        case VM_FAULT_MAJOR:
                tsk->maj_flt++;
                break;
        case VM_FAULT_SIGBUS:
                goto do_sigbus;
        default:
                goto out_of_memory;
        }

        up_read(&mm->mmap_sem);
        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:
        up_read(&mm->mmap_sem);

bad_area_nosemaphore:
        /* User mode accesses just cause a SIGSEGV */
        if (error_code & PF_USER) {
                if (is_prefetch(regs, address, error_code))
                        return;

                /* Work around K8 erratum #100 K8 in compat mode
                   occasionally jumps to illegal addresses >4GB.  We
                   catch this here 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. */
                if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) &&
                    (address >> 32))
                        return;

                if (exception_trace && unhandled_signal(tsk, SIGSEGV)) {
                        printk(
                       "%s%s[%d]: segfault at %016lx rip %016lx rsp %016lx error %lx\n",
                                        tsk->pid > 1 ? KERN_INFO : KERN_EMERG,
                                        tsk->comm, tsk->pid, address, regs->rip,
                                        regs->rsp, error_code);
                }
       
                tsk->thread.cr2 = address;
                /* Kernel addresses are always protection faults */
                tsk->thread.error_code = error_code | (address >= TASK_SIZE);
                tsk->thread.trap_no = 14;
                info.si_signo = SIGSEGV;
                info.si_errno = 0;
                /* info.si_code has been set above */
                info.si_addr = (void __user *)address;
                force_sig_info(SIGSEGV, &info, tsk);
                return;
        }

no_context:
        
        /* Are we prepared to handle this kernel fault?  */
        fixup = search_exception_tables(regs->rip);
        if (fixup) {
                regs->rip = fixup->fixup;
                return;
        }

        /* 
         * Hall of shame of CPU/BIOS bugs.
         */

        if (is_prefetch(regs, address, error_code))
                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.
 */

        flags = oops_begin();

        if (address < PAGE_SIZE)
                printk(KERN_ALERT "Unable to handle kernel NULL pointer dereference");
        else
                printk(KERN_ALERT "Unable to handle kernel paging request");
        printk(" at %016lx RIP: \n" KERN_ALERT,address);
        printk_address(regs->rip);
        dump_pagetable(address);
        tsk->thread.cr2 = address;
        tsk->thread.trap_no = 14;
        tsk->thread.error_code = error_code;
        __die("Oops", regs, error_code);
        /* Executive summary in case the body of the oops scrolled away */
        printk(KERN_EMERG "CR2: %016lx\n", address);
        oops_end(flags);
        do_exit(SIGKILL);

/*
 * We ran out of memory, or some other thing happened to us that made
 * us unable to handle the page fault gracefully.
 */
out_of_memory:
        up_read(&mm->mmap_sem);
        if (current->pid == 1) { 
                yield();
                goto again;
        }
        printk("VM: killing process %s\n", tsk->comm);
        if (error_code & 4)
                do_exit(SIGKILL);
        goto no_context;

do_sigbus:
        up_read(&mm->mmap_sem);

        /* Kernel mode? Handle exceptions or die */
        if (!(error_code & PF_USER))
                goto no_context;

        tsk->thread.cr2 = address;
        tsk->thread.error_code = error_code;
        tsk->thread.trap_no = 14;
        info.si_signo = SIGBUS;
        info.si_errno = 0;
        info.si_code = BUS_ADRERR;
        info.si_addr = (void __user *)address;
        force_sig_info(SIGBUS, &info, tsk);
        return;
}

DEFINE_SPINLOCK(pgd_lock);
struct page *pgd_list;

void vmalloc_sync_all(void)
{
        /* Note that races in the updates of insync and start aren't 
           problematic:
           insync can only get set bits added, and updates to start are only
           improving performance (without affecting correctness if undone). */
        static DECLARE_BITMAP(insync, PTRS_PER_PGD);
        static unsigned long start = VMALLOC_START & PGDIR_MASK;
        unsigned long address;

        for (address = start; address <= VMALLOC_END; address += PGDIR_SIZE) {
                if (!test_bit(pgd_index(address), insync)) {
                        const pgd_t *pgd_ref = pgd_offset_k(address);
                        struct page *page;

                        if (pgd_none(*pgd_ref))
                                continue;
                        spin_lock(&pgd_lock);
                        for (page = pgd_list; page;
                             page = (struct page *)page->index) {
                                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(*pgd) != pgd_page(*pgd_ref));
                        }
                        spin_unlock(&pgd_lock);
                        set_bit(pgd_index(address), insync);
                }
                if (address == start)
                        start = address + PGDIR_SIZE;
        }
        /* Check that there is no need to do the same for the modules area. */
        BUILD_BUG_ON(!(MODULES_VADDR > __START_KERNEL));
        BUILD_BUG_ON(!(((MODULES_END - 1) & PGDIR_MASK) == 
                                (__START_KERNEL & PGDIR_MASK)));
}

static int __init enable_pagefaulttrace(char *str)
{
        page_fault_trace = 1;
        return 1;
}
__setup("pagefaulttrace", enable_pagefaulttrace);