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    SubjectRe: unify pagetable accessors patch causes double fault II
    Andi Kleen wrote:
    > On Mon, Jan 14, 2008 at 02:46:00PM -0800, Jeremy Fitzhardinge wrote:
    >
    >> Andi Kleen wrote:
    >>
    >>>> OK, I see the problem. The problem is that the _PAGE_X defines are
    >>>> defined with _AC(UL, 1 << _PAGE_BIT_X), which has unsigned long type.
    >>>> This means that ~_PAGE_X also has unsigned long type, and so when cast
    >>>> to 64-bit in pte_mkX, it ends up &ing the pte with 0x00000000ffffffxxx,
    >>>> with predictable results.
    >>>>
    >>>>
    >>> Actually I fixed some of that -- see the pgtable-nx patch on firstfloor --
    >>> but
    >>> it still doesn't work. Or maybe my patch was not complete.
    >>>
    >>>
    >> Yeah, that looks like the right sort of thing, but I wonder if there's
    >> other places doing an open-coded "pte_val(pte) & ~_PAGE_FOO". My patch
    >> changes the definition of _PAGE_FOO so it should be OK everywhere.
    >>
    >
    > Yes that's probably better. I just hit it because NX bits went missing.
    >
    >
    >>>> The original code just used signed constants for the _PAGE_X
    >>>> definitions, which will sign-extend when cast to 64-bit, and so have the
    >>>> upper bits set when masking. (Well, actually, the old code just
    >>>> operated on pte_low, so the problem didn't arise; however, pgtable_64.h
    >>>> also uses integers for its _PAGE_X, which has the same sign-extended
    >>>> 32->64 casting property).
    >>>>
    >>>> I'll put together a fixup patch now.
    >>>>
    >>>>
    >>> I'm leaving now but can test later.
    >>>
    >>>
    >> Can you try this out? It applies after "x86: move all asm/pgtable
    >> constants into one place".
    >>
    >
    > I just applied over the whole git-x86 patchkit (tip
    > 2f42671697ea9abc7d10ea7f663d6ef6e8ec6358) + the two build fixes
    > Unfortunately it didn't work, although the faulting loop is shorter now:
    >

    Just to be clear, these two patches cause this oops to appear? Current
    x86.git seems to be missing a pile of patches at the moment, so I
    presume you're using a version which does have my patch set?

    > Freeing unused kernel memory: 260k freed
    > mount[1159]: segfault at b7fcfe98 ip b7ec6b7a sp bfcfcdec error 7
    > Eeek! page_mapcount(page) went negative! (-1)
    > page pfn = bfc33
    > page->flags = 80000014
    > page->count = 0
    > page->mapping = 00000000
    > vma->vm_ops = nfs_file_vm_ops+0x0/0x18
    > vma->vm_ops->nopage = 0x0
    > vma->vm_ops->fault = filemap_fault+0x0/0x34e
    > vma->vm_file->f_op->mmap = nfs_file_mmap+0x0/0x61
    > ------------[ cut here ]------------
    > kernel BUG at /home/lsrc/quilt/linux/mm/rmap.c:631!
    > invalid opcode: 0000 [#1] SMP
    > Modules linked in:
    >
    > Pid: 1159, comm: mount Not tainted (2.6.24-rc7 #55)
    > EIP: 0060:[<c0152a32>] EFLAGS: 00010282 CPU: 3
    > EIP is at page_remove_rmap+0xcc/0xe7
    > EAX: 00000037 EBX: c27f8660 ECX: 00000046 EDX: 00000046
    > ESI: f7061c60 EDI: f7d87380 EBP: f7060e78 ESP: f7509df8
    > DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
    > Process mount (pid: 1159, ti=f7508000 task=f7460540 task.ti=f7508000)
    > Stack: c27f8660 bfc33065 c014d166 00000000 f7061c60 f7509e80 00000000 00000000
    > 00000000 00000001 b7fd0000 f7555010 f7d87380 c482e240 00000000 ffffffff
    > c16e0c0c 00000000 00000000 f7084df8 003d5ee2 b7fd0000 b7fd0000 00000000
    > Call Trace:
    > [<c014d166>] unmap_vmas+0x349/0x5d1
    > [<c0150006>] exit_mmap+0x5f/0xcd
    > [<c011df0a>] mmput+0x25/0x79
    > [<c0122636>] do_exit+0x1a9/0x5eb
    > [<c0122ae3>] sys_exit_group+0x0/0xd
    > [<c0129dde>] get_signal_to_deliver+0x3e3/0x405
    > [<c04334b6>] do_page_fault+0x0/0x69f
    > [<c0102606>] do_notify_resume+0x7d/0x64e
    > [<c0120383>] printk+0x14/0x18
    > [<c0433874>] do_page_fault+0x3be/0x69f
    > [<c0433b4c>] do_page_fault+0x696/0x69f
    > [<c01508c1>] do_munmap+0x181/0x19b
    > [<c04334b6>] do_page_fault+0x0/0x69f
    > [<c0102f4e>] work_notifysig+0x13/0x19
    > =======================
    > Code: 8b 46 44 8b 50 08 b8 d2 95 50 c0 e8 9c ad fe ff 8b 46 4c 85 c0 74 14 8b 40 10 85 c0 74 0d 8b 50 2c b8 f0 95 50 c0 e8 81 ad fe ff <0f> 0b eb fe 8b 53 10 89 d8 5b 5e 83 e2 01 f7 da 83 c2 04 e9 c5
    > EIP: [<c0152a32>] page_remove_rmap+0xcc/0xe7 SS:ESP 0068:f7509df8
    > ---[ end trace eb3c259ee0695fdd ]---
    > Fixing recursive fault but reboot is needed!
    > eth0: no IPv6 routers present
    >
    >

    J


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