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[Qemu-devel] NetBSD doesn't boot under KVM


From: Peter Maydell
Subject: [Qemu-devel] NetBSD doesn't boot under KVM
Date: Tue, 21 Mar 2017 16:14:11 +0000

So if you try to boot NetBSD inside KVM:


 qemu-img create -f qcow2 disk.qcow2 15G
 wget http://cdn.netbsd.org/pub/NetBSD/NetBSD-7.1/images/NetBSD-7.1-amd64.iso
 qemu-system-x86_64 -m 2048 -enable-kvm \
   -drive if=virtio,file=disk.qcow2,format=qcow2 \
   -netdev user,id=mynet0,hostfwd=tcp::7722-:22 \
   -device e1000,netdev=mynet0 \
   -cdrom NetBSD-7.1-amd64.iso

the guest kernel hangs during boot. This works fine for
running on real h/w (I assume), and also if you run in
TCG by dropping -enable-kvm.

It also works if you add -smp 2 -cpu kvm64,-sse2,-cx8
because the bit that causes problems seems to be
http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/arch/x86/x86/patch.c?rev=1.2.4.3&content-type=text/x-cvsweb-markup
where x86_patch() patches various bits of the guest kernel,
and turning off those cpuid features causes it to skip the
patching.

Any ideas? Does this sound like a KVM bug, or a guest bug?

(Tested on 4.4.0-31-generic #50-Ubuntu x86-64 host kernel
and QEMU emulator version 2.5.0 (Debian 1:2.5+dfsg-5ubuntu10.8).
Yes, I know that's really old...)

thanks
-- PMM



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