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. Newer (non-RHEL 5.5) kernels boot fine without extboot, so another path to solving this bug is to bisect guest kernels. Stefan -- 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
