From mboxrd@z Thu Jan  1 00:00:00 1970
From: Avi Kivity <avi@qumranet.com>
Subject: Re: KVM: x86: do not execute halted vcpus (resend)
Date: Wed, 10 Sep 2008 21:42:05 +0300
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References: <20080908182347.GA8457@dmt.cnet> <48C68502.9010500@qumranet.com> <48C7B7BA.70405@qumranet.com> <20080910183716.GA6373@dmt.cnet>
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Cc: kvm-devel <kvm@vger.kernel.org>
To: Marcelo Tosatti <mtosatti@redhat.com>
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Marcelo Tosatti wrote:
>> Actually it does reproduce.  If you reboot twice, the second reboot will  
>> hang during reset (with cs:ip = f000:fff0).  Plain Windows XP.
>>     
>
> OK, easily reproducible by adding a sleep at the start of
> qemu_kvm_system_reset.
>
> The problem is that the vcpu HLT's between the KBD ioport write and the
> actual system reset by the IO thread. By then time there will be no
> event that takes it out of STATE_HALTED.
>
> The following fixes it, however older userspace will remain borked.
> Alternative is to special case f000:fff0 in-kernel. What is preferred?
>
>   

Special-case the kvm_set_sregs ioctl with cs:eip f000:fff0 (and cr0.pe=0
for good measure).

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.