At 07/23/2012 07:50 AM, Sasha Levin Wrote: > On 07/23/2012 12:36 AM, Anthony Liguori wrote: >> Sasha Levin <levinsasha928@xxxxxxxxx> writes: >> >>> On 07/22/2012 09:14 PM, Anthony Liguori wrote: >>>> Sasha Levin <levinsasha928@xxxxxxxxx> writes: >>>> >>>>> On 07/21/2012 10:44 AM, Wen Congyang wrote: >>>>>> We can know the guest is panicked when the guest runs on xen. >>>>>> But we do not have such feature on kvm. >>>>>> >>>>>> Another purpose of this feature is: management app(for example: >>>>>> libvirt) can do auto dump when the guest is panicked. If management >>>>>> app does not do auto dump, the guest's user can do dump by hand if >>>>>> he sees the guest is panicked. >>>>>> >>>>>> We have three solutions to implement this feature: >>>>>> 1. use vmcall >>>>>> 2. use I/O port >>>>>> 3. use virtio-serial. >>>>>> >>>>>> We have decided to avoid touching hypervisor. The reason why I choose >>>>>> choose the I/O port is: >>>>>> 1. it is easier to implememt >>>>>> 2. it does not depend any virtual device >>>>>> 3. it can work when starting the kernel >>>>> >>>>> Was the option of implementing a virtio-watchdog driver considered? >>>>> >>>>> You're basically re-implementing a watchdog, a guest-host interface and a set of protocols for guest-host communications. >>>>> >>>>> Why can't we re-use everything we have now, push a virtio watchdog >>>>> driver into drivers/watchdog/, and gain a more complete solution to >>>>> detecting hangs inside the guest. >>>> >>>> The purpose of virtio is not to reinvent every possible type of device. >>>> There are plenty of hardware watchdogs that are very suitable to be used >>>> for this purpose. QEMU implements quite a few already. >>>> >>>> Watchdogs are not performance sensitive so there's no point in using >>>> virtio. >>> >>> The issue here is not performance, but the adding of a brand new >>> guest-host interface. >> >> We have: >> >> 1) Virtio--this is our preferred PV interface. It needs PCI to be fully >> initialized and probably will live as a module. >> >> 2) Hypercalls--this a secondary PV interface but is available very >> early. It's terminated in kvm.ko which means it can only operate on >> things that are logically part of the CPU and/or APIC complex. >> >> This patch introduces a third interface which is available early like >> hypercalls but not necessarily terminated in kvm.ko. That means it can >> have a broader scope in functionality than (2). >> >> We could just as well use a hypercall and have multiple commands issued >> to that hypercall as a convention and add a new exit type to KVM that >> sent that specific hypercall to userspace for processing. >> >> But a PIO operation already has this behavior and requires no changes to kvm.ko. > > I don't dispute that there may be a need for another guest-host interface, but this patch can basically be called "kvm: notify host when the guest is panicked, oh, btw, and add a brand new undocumented interface" I forgot to document this interface. I will add it. Thanks Wen Congyang > > The new interface should at least come in it's own patch, with documentation. > -- > 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
