于 2012年05月21日 17:36, Avi Kivity 写道: > On 05/21/2012 12:08 PM, Yanfei Zhang wrote: >> 于 2012年05月21日 16:34, Avi Kivity 写道: >>> On 05/21/2012 05:32 AM, Yanfei Zhang wrote: >>>> 于 2012年05月21日 01:43, Avi Kivity 写道: >>>>> On 05/16/2012 10:50 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 slove this problem >>>>>> by reverse engineering implemented in this patch set. The VMCSINFO >>>>>> is exported via sysfs to kexec-tools just like VMCOREINFO. >>>>>> >>>>>> Here are two usercases for two features that we want. >>>>>> >>>>>> 1) Create guest machine's crash dumpfile from host machine's crash dumpfile >>>>>> >>>>>> In general, we want to use this feature on failure analysis for the system >>>>>> where the processing depends on the communication between host and guest >>>>>> machines to look into the system from both machines's viewpoints. >>>>>> >>>>>> As a concrete situation, consider where there's heartbeat monitoring >>>>>> feature on the guest machine's side, where we need to determine in >>>>>> which machine side the cause of heartbeat stop lies. In our actual >>>>>> experiments, we encountered such situation and we found the cause of >>>>>> the bug was in host's process schedular so guest machine's vcpu stopped >>>>>> for a long time and then led to heartbeat stop. >>>>>> >>>>>> The module that judges heartbeat stop is on guest machine, so we need >>>>>> to debug guest machine's data. But if the cause lies in host machine >>>>>> side, we need to look into host machine's crash dump. >>>>> >>>>> Do you mean, that a heartbeat failure in the guest lead to host panic? >>>>> >>>>> My expectation is that a problem in the guest will cause the guest to >>>>> panic and perhaps produce a dump; the host will remain up. >>>>> >>>> >>>> The point is that before our investigation, we didn't know which side >>>> leads to this buggy situation. Maybe a bug in host machine or the guest >>>> machine itself causes a heartbeat failure. >>> >>> How can a guest bug cause a host panic? >>> >>>> So we want to get both host machine's crash dump and guest machine's >>>> crash dump *at the same time*. Then we could use userspace tools to >>>> get guest machine crash dump from host machine's and analyse them >>>> separately to find which side causes the problem. >>>> >>> >>> If the guest caused the problem, there would be no panic; therefore >>> there was a host bug. >>> >> >> Yes, a guest bug cannot cause a host panic. When heartbeat stops in guest >> machine, we could trigger the host dump mechanism to work. This is because >> we want to get the status of both host and guest machine at the same time >> when heartbeat stops in guest machine. Then we can look for bug reasons >> from both host machine's and guest machine's views. > > That sounds like a bad idea. Can you explain in what situation it makes > sense for a guest to stop the host (and all other guests running on it) > rather than just restarting the failed services (on the host or other > guests)? > We never do this on customer's environment which maybe a host with many guests running on it. We do this on another environment to reproduce the buggy situation; or we do this in testing phase on development environment towards production one on the customer's site. >>>>>> Without this feature, we first create guest machine's dump and then >>>>>> create host mahine's, but there's only a short time between two >>>>>> processings, during which it's unlikely that buggy situation remains. >>>>>> >>>>>> So, we think the feature is useful to debug both guest machine's and >>>>>> host machine's sides at the same time, and expect we can make failure >>>>>> analysis efficiently. >>>>>> >>>>>> Of course, we believe this feature is commonly useful on the situation >>>>>> where guest machine doesn't work well due to something of host machine's. >>>>>> >>>>>> 2) Get offsets of VMCS information on the CPU running on the host machine >>>>>> >>>>>> If kdump doesn't work well, then it means we cannot use kvm API to get >>>>>> register values of guest machine and they are still left on its vmcs >>>>>> region. In the case, we use crash dump mechanism running outside of >>>>>> linux kernel, such as sadump, a firmware-based crash dump. Then VMCS >>>>>> information is then necessary. >>>>> >>>>> Shouldn't sadump then expose the VMCS offsets? Perhaps bundling them >>>>> into its dump file? >>>>> >>>> >>>> Firmware-based crash dump doesn't concern the os running on the machine. >>>> So it will not do any os handling when machine crashes. >>> >>> Seems to me the VMCS offsets are OS independent. >>> >> Hmm, you mean we could get VMCS offsets in sadump itself? >> But I think if we just export VMCS offsets in kernel, we could use the current >> existing dump tools with no or just very tiny change. I think this could be >> a more general mechanism than making changes in all kinds of dump tools. > > The sadump tool generates a core file with the OS image, right? Can it > not attach the offsets to a note, just like you propose for kdump? > Both are right. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
