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. Thanks Wen Congyang > > -- > Gleb. > -- 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
