Re: [Qemu-devel] [RFC][PATCT 0/5 v2] dump memory when host pci device is used by guest

[Wen Congyang]

Hi, hatayama-san

At 12/13/2011 11:12 AM, HATAYAMA Daisuke Write:
> Hello Wen,
> 
> From: Wen Congyang <address@hidden>
> Subject: [Qemu-devel] [RFC][PATCT 0/5 v2] dump memory when host pci device is 
> used by guest
> Date: Fri, 09 Dec 2011 15:57:26 +0800
> 
>> Hi, all
>>
>> 'virsh dump' can not work when host pci device is used by guest. We have
>> discussed this issue here:
>> http://lists.nongnu.org/archive/html/qemu-devel/2011-10/msg00736.html
>>
>> We have determined to introduce a new command dump to dump memory. The core
>> file's format can be elf.
>>
>> Note:
>> 1. The guest should be x86 or x86_64. The other arch is not supported.
>> 2. If you use old gdb, gdb may crash. I use gdb-7.3.1, and it does not crash.
>> 3. If the OS is in the second kernel, gdb may not work well, and crash can
>>    work by specifying '--machdep phys_addr=xxx' in the command line. The
>>    reason is that the second kernel will update the page table, and we can
>>    not get the page table for the first kernel.
> 
> I guess still the current implementation breaks vmalloc'ed area that
> needs page tables originally located in the first 640kB, right? If you
> want to do so in a correct way, you need to identify a position of
> backup region and get data of 1st kernel's page tables.

I do not know anything about vmalloc'ed area. Can you explain it more
detailed?

> 
> But it needs debugging information of guest kernel, and I don't think
> it good idea that qemu uses too guest-specific information.
> 
> On the other hand, I have a basic question. Can this command used for
> creating live dump? or crash dump only?

Do you mean dump guest's memory while it is running(do not stop the guest)?
If so, this command can not be used for creating live dump.

Thanks
Wen Congyang

> 
> Thanks.
> HATAYAMA, Daisuke
> 
>