[SeaBIOS] [Qemu-devel] [PATCH] SeaBios: Fix reset procedure reentrancy problem on qemu-kvm platform

Kevin O'Connor kevin at koconnor.net
Wed Nov 4 18:42:02 CET 2015

On Wed, Nov 04, 2015 at 08:48:20AM +0800, Gonglei wrote:
> On 2015/11/3 14:58, Xulei (Stone, Euler) wrote:
> > On qemu-kvm platform, when I reset a VM through "virsh reset", and coincidently
> > the VM is in process of internal rebooting at the same time. Then the VM will
> > not be successfully reseted any more due to the reset reentrancy. I found:
> > (1)SeaBios try to shutdown the VM after reseting it failed by apm_shutdown().
> > However, apm_shutdown() does not work on qemu-kvm platform;
> > (2)I add 1s sleep in qemu_prep_reset(), then continuously reset the VM twice,
> > aforementioned case must happen.

So, the problem occurs when issuing a second reset before the first
reset completes?

> > This patch fixes this issue by letting the VM always execute the reboot
> > routing while a reenrancy happenes instead of attempting apm_shutdown on
> > qemu-kvm platform.

The reason for the HaveAttemptedReboot check is to work around old
versions of KVM that unexpectedly map the same memory to both 0xf0000
and 0xffff0000.  So, it does not make sense to wrap the check in a
!runningOnKVM() block as that disables the only reason for the check.

I'm surprised you would see the above on a recent qemu/kvm though - as
on a newer KVM I think the second reset would have to happen after
HaveAttemptedReboot is set and prior to the memcpy in
qemu_prep_reset() completing.  Can you verify your KVM version?


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