linux-kernel - Re: bad paravirt/Xen interaction in "x86 - Enhance DEBUG_RODATA support

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Date:	Mon, 3 Mar 2008 15:53:33 -0500
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Andi Kleen <ak@...e.de>, "H. Peter Anvin" <hpa@...or.com>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Zachary Amsden <zach@...are.com>
Subject: Re: bad paravirt/Xen interaction in "x86 - Enhance DEBUG_RODATA
	support - alternatives"

* Jeremy Fitzhardinge (jeremy@...p.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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