From: Yanfei Zhang Subject: Re: [PATCH v2 0/5] Export offsets of VMCS fields as note information for kdump Date: Mon, 21 May 2012 10:32:13 +0800 Message-ID: <4FB9A92D.7050108@cn.fujitsu.com> References: <4FB35C48.30708@cn.fujitsu.com> <4FB92D5A.3060507@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=GB2312 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: mtosatti@redhat.com, ebiederm@xmission.com, luto@mit.edu, Joerg Roedel , dzickus@redhat.com, paul.gortmaker@windriver.com, ludwig.nussel@suse.de, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, kexec@lists.infradead.org, Greg KH To: Avi Kivity Return-path: In-Reply-To: <4FB92D5A.3060507@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org =D3=DA 2012=C4=EA05=D4=C221=C8=D5 01:43, Avi Kivity =D0=B4=B5=C0: > On 05/16/2012 10:50 AM, zhangyanfei wrote: >> This patch set exports offsets of VMCS fields as note information fo= r >> 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 intern= al >> 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 d= umpfile >> >> In general, we want to use this feature on failure analysis for the = system >> where the processing depends on the communication between host and g= uest >> 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 stop= ped >> for a long time and then led to heartbeat stop. >> >> The module that judges heartbeat stop is on guest machine, so we nee= d >> 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. >=20 > Do you mean, that a heartbeat failure in the guest lead to host panic= ? >=20 > 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. >=20 The point is that before our investigation, we didn't know which side=20 leads to this buggy situation. Maybe a bug in host machine or the guest machine itself causes a heartbeat failure. 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. >> 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= =2E >> >> 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 failur= e >> analysis efficiently. >> >> Of course, we believe this feature is commonly useful on the situati= on >> where guest machine doesn't work well due to something of host machi= ne's. >> >> 2) Get offsets of VMCS information on the CPU running on the host ma= chine >> >> If kdump doesn't work well, then it means we cannot use kvm API to g= et >> 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. >=20 > Shouldn't sadump then expose the VMCS offsets? Perhaps bundling them > into its dump file? >=20 =46irmware-based crash dump doesn't concern the os running on the machi= ne. So it will not do any os handling when machine crashes. Thanks Zhang Yanfei =20