Re: [PATCH 0/4] Export offsets of VMCS fields as note informationfor kdump

From: Anthony Liguori
Date: Tue Apr 17 2012 - 12:50:01 EST

On 04/17/2012 02:44 AM, Avi Kivity wrote:
On 04/11/2012 04:39 AM, zhangyanfei wrote:
This patch set exports offsets of VMCS fields as note information for
kdump. We call it VMCSINFO. The purpose of VMCSINFO is to retrieve
runtime state of guest machine image, such as registers, in host
machine's crash dump as VMCS format. The problem is that VMCS
internal is hidden by Intel in its specification. So, we reverse
engineering it in the way implemented in this patch set. Please note
that this processing never affects any existing kvm logic. The
VMCSINFO is exported via sysfs to kexec-tools just like VMCOREINFO.

Here is an example:
Processor: Intel(R) Core(TM)2 Duo CPU E7500 @ 2.93GHz

$cat /sys/kernel/vmcsinfo
1cba8c0 2000

crash> rd -p 1cba8c0 1000
1cba8c0: 0000127b00000009 53434d5600000000 ....{.......VMCS
1cba8d0: 000000004f464e49 4e4f495349564552 INFO....REVISION
1cba8e0: 49460a643d44495f 5f4e495028444c45 _ID=d.FIELD(PIN_
1cba8f0: 4d565f4445534142 4f435f434558455f BASED_VM_EXEC_CO
1cba900: 303d294c4f52544e 0a30383130343831 NTROL)=01840180.
1cba910: 504328444c454946 5f44455341425f55 FIELD(CPU_BASED_
1cba920: 5f434558455f4d56 294c4f52544e4f43 VM_EXEC_CONTROL)
1cba930: 393130343931303d 28444c4549460a30 =01940190.FIELD(
1cba940: 5241444e4f434553 4558455f4d565f59 SECONDARY_VM_EXE
1cba950: 4f52544e4f435f43 30346566303d294c C_CONTROL)=0fe40
1cba960: 4c4549460a306566 4958455f4d562844 fe0.FIELD(VM_EXI
1cba970: 4f52544e4f435f54 346531303d29534c T_CONTROLS)=01e4
1cba980: 4549460a30653130 4e455f4d5628444c 01e0.FIELD(VM_EN
1cba990: 544e4f435f595254 33303d29534c4f52 TRY_CONTROLS)=03
1cba9a0: 460a303133303431 45554728444c4549 140310.FIELD(GUE
1cba9b0: 45535f53455f5453 3d29524f5443454c ST_ES_SELECTOR)=
1cba9c0: 4549460a30303530 545345554728444c 0500.FIELD(GUEST
1cba9d0: 454c45535f53435f 35303d29524f5443 _CS_SELECTOR)=05

1. In kexec-tools, get VMCSINFO via sysfs and dump it as note information
into vmcore.
2. Dump VMCS region of each guest vcpu and VMCSINFO into qemu-process
core file. To do this, we will modify kernel core dumper, gdb gcore
and crash gcore.
3. Dump guest image from the qemu-process core file into a vmcore.

Taking a step back, can you describe the problem scenario you're fixing

Note that assuming that VMCS fields map to offsets within memory is not guaranteed to work for future processors.

There is no guarantee that fields won't be compressed or stored with inverted bit ordering.


Anthony Liguori

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at