Messages in this thread | | | Date | Fri, 22 Aug 2008 13:45:29 -0400 | From | Mathieu Desnoyers <> | Subject | Re: 2.6.{26.2,27-rc} oops on virtualbox |
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* H. Peter Anvin (hpa@zytor.com) wrote: > Was looking at the code stream, and noticed this: > > Code: c0 0f 84 0b 01 00 00 b8 d0 bf 41 c0 c7 05 6c c0 41 c0 ff ff ff ff e8 > 7f 82 21 00 e8 1a 03 02 00 8b 45 b0 50 9d 0f 1f 84 00 00 00 <00> 00 8b 45 > bc 83 c4 60 5b 5e 5f 5d c3 66 90 a1 6c c0 41 c0 e8 > > Code: c0 0f 84 0b 01 00 00 b8 d0 bf 41 c0 c7 05 6c c0 41 c0 ff ff ff ff e8 > 7f 82 21 00 e8 1a 03 02 00 8b 45 b0 50 9d 0f 1f 84 00 00 00 <00> 00 8b 45 > bc 83 c4 60 5b 5e 5f 5d c3 66 90 a1 6c c0 41 c0 e8 > > The EIP is in the *MIDDLE* of a NOPL instruction: > > C012FC46 C00F84 ror byte [edi],0x84 > C012FC49 0B01 or eax,[ecx] > C012FC4B 0000 add [eax],al > C012FC4D B8D0BF41C0 mov eax,0xc041bfd0 > C012FC52 C7056CC041C0FFFF mov dword [dword 0xc041c06c],0xffffffff > -FFFF > C012FC5C E87F822100 call dword 0xc0347ee0 > C012FC61 E81A030200 call dword 0xc014ff80 > C012FC66 8B45B0 mov eax,[ebp-0x50] > C012FC69 50 push eax > C012FC6A 9D popfd > C012FC6B 0F1F840000000000 nop dword [eax+eax+0x0] > C012FC73 8B45BC mov eax,[ebp-0x44] > C012FC76 83C460 add esp,byte +0x60 > C012FC79 5B pop ebx > C012FC7A 5E pop esi > C012FC7B 5F pop edi > C012FC7C 5D pop ebp > C012FC7D C3 ret > C012FC7E 6690 xchg ax,ax > C012FC80 A16CC041C0 mov eax,[0xc041c06c] > > There are two possibilities: VirtualBox mis-executes (not merely traps, > which is what tip:master looks for) the NOPL instruction, or something is > jumping into the middle of the sequence that is then replaced by the NOPL. > > So, Luiz: the DEBUG_INFO version of vmlinux would be helpful. It would > also help to know the exact version of VirtualBox you're running, what > source you got it from, and what your host system looks like. > > -hpa
The patch which turns on this bug this this important change to the apply paravirt : it disables interrupts _near_ the code patching, _within_ the loop. Before, interrupts were disabled outside of the loop. It needs to disable interrupts within the loop to be able to use vmap in text_poke().
So I bet VirtualBox has a race in the way it handles interrupt disabling.
Mathieu
-- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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