On Mon, Jul 05, 2010 at 01:36:08PM +0100, Stefan Hajnoczi wrote: > 2010/7/5 Gleb Natapov <gleb@xxxxxxxxxx>: > > On Mon, Jul 05, 2010 at 01:11:25PM +0100, Stefan Hajnoczi wrote: > >> On Fri, Jul 2, 2010 at 9:07 AM, Stefan Hajnoczi <stefanha@xxxxxxxxx> wrote: > >> > On Fri, Jul 2, 2010 at 4:31 AM, ewheeler <kvm@xxxxxxxxxxxxxxx> wrote: > >> >> Hello all, > >> >> > >> >> I'm booting a CentOS kernel under today's KVM git and it hangs after > >> >> initializing the serial port when the drive if=virtio, but not when > >> >> drive if=ide. Look close---this is not a "forgot to add virtio_blk" > >> >> problem. If I use 0.12.3 from Ubuntu 10.04 it works properly. > >> >> > >> >> Reproduction: > >> >> > >> >> Using kvm 0.12.3 on ubuntu 10.04 (1:84+dfsg-0ubuntu16+0.12.3+noroms > >> >> +0ubuntu9) it will work properly: > >> >> > >> >> qemu-system-x86_64 -drive file=dummy-disk-image,if=virtio \ > >> >> -kernel vmlinuz-2.6.18-194.3.1.el5.centos.plus > >> >> > >> >> As expected, the kernel panics unable to mount root (good-boot.png). > >> >> This makes sense, as "dummy-disk-image" is 1MB of 0x00 bytes. > >> >> > >> >> ---However---if I use today's git (2010-07-01) of kvm: > >> >> > >> >> /usr/local/kvm-git/bin/qemu-system-x86_64 -drive file=dummy-disk-image,if=virtio \ > >> >> -kernel vmlinuz-2.6.18-194.3.1.el5.centos.plus > >> >> > >> >> This hangs just after initializing the Serial device (obtained by adding > >> >> -serial stdio -append console=ttyS0): > >> >> > >> >> Note that this only happens with the disk interface set to virtio > >> >> (if=virtio). It works fine for ide (if=ide). > >> >> > >> >> > >> >> Am I doing something wrong here? > >> >> Is anyone else having this problem? > >> > > >> > I have seen this issue with a RHEL 5.5 guest running under > >> > qemu-kvm.git. It boots a new guest fine but hangs as you described > >> > with the RHEL 5.5 kernel. I have not investigated. > >> > >> This issue is affected by extboot, a feature that enables booting from > >> virtio-blk devices. I have just sent a patch to the KVM mailing list > >> to restore extboot functionality which has been broken in > >> qemu-kvm.git. That patch can be used to work around this issue by > >> using "-drive ...,boot=on" but it doesn't explain why the RHEL 5.5 > >> kernel hangs during serial initialization when extboot is not present. > >> > > Hang that happens during guest boot (after bootloader started the > > kernel) cannot be worked around by extboot. extboot is also not needed > > with latest qemu git to boot from virtio disks since the support for > > that is in the bios now. > > I agree that something else is going on here and needs to be > investigated, but I do think that extboot can indirectly affect the > guest boot. > > With extboot the virtio-blk PCI adapter is not touched by the > firmware/bootloader. Is it possible that a virtio-blk interrupt is > raised and not acknowledged before entering Linux. When Linux brings > up the serial port it gets swamped with interrupts? That's just a > guess. > That is possible when bios is actually used to boot the guest, but bug reporter uses -kernel option so no bios boot code should run at all. Virtio is initialized anyway, but this will happen with boot=on too. > Newer (non-RHEL 5.5) kernels boot fine without extboot, so another > path to solving this bug is to bisect guest kernels. > > Stefan -- 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
