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    SubjectRe: bad paravirt/Xen interaction in "x86 - Enhance DEBUG_RODATA support - alternatives"
    * Jeremy Fitzhardinge (jeremy@goop.org) wrote:
    > Andi Kleen wrote:
    >> On Monday 03 March 2008 18:58:03 Jeremy Fitzhardinge wrote:
    >>
    >>
    >>> Perhaps, though that's uncached by default.
    >>>
    >>
    >> ioremap_cached()
    >
    > Sure. But given that from the perspective of this problem ioremap* is just
    > a wrapper for vmap, we may as well use it directly and avoid getting
    > tangled up in any current or future io-related stuff that ioremap may want
    > to do.
    >
    > J

    Would you have a quick hint on why I get a page fault with the following
    implementation ? There is probably a fundamental detail I missed.


    void *__kprobes text_poke(void *addr, const void *opcode, size_t len)
    {
    char *vaddr;
    struct page *pages[1];

    BUG_ON(len > sizeof(long));
    BUG_ON((((long)addr + len - 1) & ~(sizeof(long) - 1))
    - ((long)addr & ~(sizeof(long) - 1)));
    if (kernel_text_address((unsigned long)addr))
    pages[0] = virt_to_page(addr);
    else
    vaddr = addr;
    vaddr = vmap(pages, 1, VM_MAP, PAGE_KERNEL);
    memcpy(&vaddr[(unsigned long)addr & PAGE_MASK], opcode, len);
    if (kernel_text_address((unsigned long)addr))
    vunmap(vaddr);
    sync_core();
    /* Could also do a CLFLUSH here to speed up CPU recovery; but
    that causes hangs on some VIA CPUs. */
    return addr;
    }


    [ 0.149856] SMP alternatives: switching to UP code
    [ 0.152009] BUG: unable to handle kernel paging request at b8902000
    [ 0.152009] IP: [<c03acfa1>] text_poke+0x85/0xb4
    [ 0.152009] *pde = 00000000
    [ 0.152009] Oops: 0002 [#1] SMP
    [ 0.152009] LTT NESTING LEVEL : 0 <0>
    [ 0.152009] Modules linked in:
    [ 0.152009]
    [ 0.152009] Pid: 0, comm: swapper Not tainted (2.6.25-rc3-testssmp #744)
    [ 0.152009] EIP: 0060:[<c03acfa1>] EFLAGS: 00010002 CPU: 0
    [ 0.152009] EIP is at text_poke+0x85/0xb4
    [ 0.152009] EAX: f8800000 EBX: 00000001 ECX: 00000001 EDX: f8800000
    [ 0.152009] ESI: c04a3fab EDI: b8902000 EBP: c0102114 ESP: c04a3f88
    [ 0.152009] DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
    [ 0.152009] Process swapper (pid: 0, ti=c04a2000 task=c04703a0 task.ti=c04a2)
    [ 0.152009] Stack: 00000163 f8800000 c1002040 c04a400c c04a7cac c0100000 c03
    [ 0.152009] 90411244 00000206 c04e072c c17fb72c 0000672c c04aaefe c03
    [ 0.152009] c04ab76a c17f5000 c04a896a 00000092 c04a80d7 00000008 000
    [ 0.152009] Call Trace:
    [ 0.152009] [<c03b0139>] _etext+0x0/0xf7ec7
    [ 0.152009] [<c0107814>] alternatives_smp_unlock+0x57/0x59
    [ 0.152009] [<c04aaefe>] alternative_instructions+0x152/0x157
    [ 0.152009] [<c03b0139>] _etext+0x0/0xf7ec7
    [ 0.152009] [<c04ab76a>] check_bugs+0x131/0x14e
    [ 0.152009] [<c04a896a>] start_kernel+0x2d1/0x327
    [ 0.152009] [<c04a80d7>] unknown_bootoption+0x0/0x1e3
    [ 0.152009] =======================
    [ 0.152009] Code: b9 04 00 00 00 ba 01 00 00 00 e8 a6 87 db ff 89 44 24 04 8
    [ 0.152009] EIP: [<c03acfa1>] text_poke+0x85/0xb4 SS:ESP 0068:c04a3f88
    [ 0.152009] ---[ end trace ca143223eefdc828 ]---
    [ 0.152009] Kernel panic - not syncing: Attempted to kill the idle task!


    Mathieu

    --
    Mathieu Desnoyers
    Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
    OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68


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