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

[HATAYAMA Daisuke]

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.

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?

Thanks.
HATAYAMA, Daisuke