On 2012-03-15 11:39, Gleb Natapov wrote: > On Wed, Mar 14, 2012 at 11:46:08AM -0700, Eric Northup wrote: >> On Wed, Mar 14, 2012 at 6:25 AM, Gleb Natapov <gleb@xxxxxxxxxx> wrote: >> >>> On Wed, Mar 14, 2012 at 03:16:05PM +0200, Avi Kivity wrote: >>>> On 03/14/2012 03:14 PM, Gleb Natapov wrote: >>>>> On Wed, Mar 14, 2012 at 03:07:46PM +0200, Avi Kivity wrote: >>>>>> On 03/14/2012 01:11 PM, Wen Congyang wrote: >>>>>>>> >>>>>>>> I don't think we want to use the driver. Instead, have a small >>> piece of >>>>>>>> code that resets the device and pushes out a string (the panic >>> message?) >>>>>>>> without any interrupts etc. >>>>>>>> >>>>>>>> It's still going to be less reliable than a hypercall, I agree. >>>>>>> >>>>>>> Do you still want to use complicated and less reliable way? >>>>>> >>>>>> Are you willing to try it out and see how complicated it really is? >>>>>> >>>>>> While it's more complicated, it's also more flexible. You can >>>>>> communicate the panic message, whether the guest is attempting a >>> kdump >>>>>> and its own recovery or whether it wants the host to do it, etc., you >>>>>> can communicate less severe failures like oopses. >>>>>> >>>>> hypercall can take arguments to achieve the same. >>>> >>>> It has to be designed in advance; and every time we notice something's >>>> missing we have to update the host kernel. >>>> >>> >>> We and in the designed stage now. Not to late to design something flexible >>> :) Panic hypercall can take GPA of a buffer where host puts panic info >>> as a parameter. This buffer can be read by QEMU and passed to management. >>> >> >> If a host kernel change is in the works, I think it might be cleanest to >> have the host kernel export a new kind of VCPU exit for unhandled-by-KVM >> hypercalls. Then usermode can respond to the hypercall as appropriate. >> This would permit adding or changing future hypercalls without host kernel >> changes. >> > There was such vm exit (KVM_EXIT_HYPERCALL), but it was deemed to be a > bad idea. BTW, this would help a lot in emulating hypercalls of other hypervisors (or of KVM's VAPIC in the absence of in-kernel irqchip - I had to jump through hoops therefore) in user space. Not all those hypercall handlers actually have to reside in the KVM module. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux -- 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
