At 03/14/2012 06:58 PM, Gleb Natapov Wrote: > On Wed, Mar 14, 2012 at 06:57:59PM +0800, Wen Congyang wrote: >> At 03/14/2012 06:52 PM, Gleb Natapov Wrote: >>> On Wed, Mar 14, 2012 at 06:52:07PM +0800, Wen Congyang wrote: >>>> At 03/14/2012 06:37 PM, Amit Shah Wrote: >>>>> On (Wed) 14 Mar 2012 [17:53:00], Wen Congyang wrote: >>>>>> At 03/14/2012 05:24 PM, Avi Kivity Wrote: >>>>>>> On 03/14/2012 10:29 AM, Wen Congyang wrote: >>>>>>>> At 03/13/2012 06:47 PM, Avi Kivity Wrote: >>>>>>>>> On 03/13/2012 11:18 AM, Daniel P. Berrange wrote: >>>>>>>>>> On Mon, Mar 12, 2012 at 12:33:33PM +0200, Avi Kivity wrote: >>>>>>>>>>> On 03/12/2012 11:04 AM, Wen Congyang wrote: >>>>>>>>>>>> Do you have any other comments about this patch? >>>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> Not really, but I'm not 100% convinced the patch is worthwhile. It's >>>>>>>>>>> likely to only be used by Linux, which has kexec facilities, and you can >>>>>>>>>>> put talk to management via virtio-serial and describe the crash in more >>>>>>>>>>> details than a simple hypercall. >>>>>>>>>> >>>>>>>>>> As mentioned before, I don't think virtio-serial is a good fit for this. >>>>>>>>>> We want something that is simple & guaranteed always available. Using >>>>>>>>>> virtio-serial requires significant setup work on both the host and guest. >>>>>>>>> >>>>>>>>> So what? It needs to be done anyway for the guest agent. >>>>>>>>> >>>>>>>>>> Many management application won't know to make a vioserial device available >>>>>>>>>> to all guests they create. >>>>>>>>> >>>>>>>>> Then they won't know to deal with the panic event either. >>>>>>>>> >>>>>>>>>> Most administrators won't even configure kexec, >>>>>>>>>> let alone virtio serial on top of it. >>>>>>>>> >>>>>>>>> It should be done by the OS vendor, not the individual admin. >>>>>>>>> >>>>>>>>>> The hypercall requires zero host >>>>>>>>>> side config, and zero guest side config, which IMHO is what we need for >>>>>>>>>> this feature. >>>>>>>>> >>>>>>>>> If it was this one feature, yes. But we keep getting more and more >>>>>>>>> features like that and we bloat the hypervisor. There's a reason we >>>>>>>>> have a host-to-guest channel, we should use it. >>>>>>>>> >>>>>>>> >>>>>>>> I donot know how to use virtio-serial. >>>>>>> >>>>>>> I don't either, copying Amit. >>>>>>> >>>>>>>> I start vm like this: >>>>>>>> qemu ...\ >>>>>>>> -device virtio-serial \ >>>>>>>> -chardev socket,path=/tmp/foo,server,nowait,id=foo \ >>>>>>>> -device virtserialport,chardev=foo,name=port1 ... >>>>>>>> >>>>>>>> You said that there are too many channels. Does it mean /tmp/foo is a channel? >>>>>>> >>>>>>> Probably. >>>>>> >>>>>> Hmm, if we use virtio-serial, the guest kernel writes something into the channel when >>>>>> the os is panicked. Is it right? >>>>> >>>>> Depends on how you want to use it. It could be the kernel, or it >>>>> could be a userspace program which monitors syslogs for panic >>>>> information and passes on that info to the virtio-serial channel. >>>> >>>> When the kernel is panicked, we cannot use userspace program. >>>> >>>>> >>>>>> If so, is this channel visible to guest userspace? If the channle is visible to guest >>>>>> userspace, the program running in userspace may write the same message to the channel. >>>>> >>>>> Access control is via permissions. You can have udev scripts assign >>>>> whatever uid and gid to the port of your interest. By default, all >>>>> ports are only accessible to the root user. >>>> >>>> We should also prevent root user writing message to this channel if it is >>>> used for panicked notification. >>>> >>> Why? Root user can also call panic hypercall if he wishes so. >> >> IIRC, the instruction vmcall needs to run on ring0. The root user is in ring3. >> > And who will stop the root from loading kernel module? Yes, I forgot this. Thanks Wen Congyang > > -- > Gleb. > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- 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
