[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Re: [PATCH]: kexec: framework and i386
Hi, > > > In summary, for kdump "linux crashdump=64M@16M" > > > becomes "xen kdump_megabytes=64 kdump_megabytes_base=16" > > > > Please can you explain a bit about how kdump works, and why a physically > > contiguous region with known base address is required. What actually > > gets written out in the crash dump and in what format? > > The reserved region is the memory space for the "dump kernel". I believe the > base address has to correspond to the base address compiled into the dump > kernel - since we don't want the dump kernel to try to own all of memory. > It's native Linux, so it likes to run in contiguous memory. The current implementation of linux kernel for x86 requires: 1. Memory for the kernel have to be physically contiguous. 2. The physical memory have to be mapped to specific virtual space. It assumes: virtual address for the kernel == physical address | 0x80000000. > When a panic occurs, Linux kexec jumps into the preloaded kdump kernel (if > any). This kernel then reinitiases the hardware, using its own device > drivers and uses these to write out the dump to disk. ISTR that the dump > format is currently ELF, although I remember some talk on the Fastboot ML > about adding some extra headers to make OS debugging easier. > > It's a nice solution because you don't rely on the hosed kernel to do the > dump > for you, and you don't disturb its state in the process. It also makes it > easy to do things like dumping to network devices, etc. > > In our case it has the added bonus that on dom0 *or* a Xen crash it ought to > be possible to kexec into a native Linux kernel which could dump (possibly > some configurable combination of) Xen itself, dom0, and all the other > domains. Admittedly hypervisor crashes / hangs are rare, but it might aid > debugging to be able to get a reliable dump of a crashed / hung Xen. > > This would also integrate with the Linux dump infrastructure, which would be > useful to have. After the dump, I think you will be able to kexec a new Xen and dom0 to restart the box automatically. > > Tim Deegan submitted a patch to add support for multiboot images (such > > as Xen) to kexec a couple of years ago, and I believe it has been part > > of the standard package for some time. > > It was in there last time I looked at the source code... I've never actually > used it though, so in principle I guess it could have rotted. Or there could > just be something weird happenning. > > Cheers, > Mark Thanks, Hirokazu Takahashi. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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