error while loading state for instance 0x0 of device 'kvmclock'

error while loading state for instance 0x0 of device 'kvmclock'

[Jan Kiszka]

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Hi,

current qemu-kvm.git gives me the message "qemu: warning: error while
loading state for instance 0x0 of device 'kvmclock'" when I run a simple
"savevm" followed by a "loadvm 1". What's broken here?

Jan


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Re: error while loading state for instance 0x0 of device 'kvmclock'

[Jan Kiszka]

Jan Kiszka wrote:
> Hi,
> 
> current qemu-kvm.git gives me the message "qemu: warning: error while
> loading state for instance 0x0 of device 'kvmclock'" when I run a simple
> "savevm" followed by a "loadvm 1". What's broken here?

OK, this is due to "KVM: add flags to kvm_clock_data" (958b0c5497): the
flags field is not cleared on KVM_SET_CLOCK. Will post a fix.

But the above kernel commit is also broken: KVM_GET_CLOCK checks
uninitialized user_ns.flags (probably instead of the user's value). This
raises the question if the caller of KVM_GET_CLOCK is also supposed to
pass kvm_clock_data with flags cleared down to the kernel. Could someone
clarify this so I could fix it accordingly?

Jan

-- 
Siemens AG, Corporate Technology, CT SE 2
Corporate Competence Center Embedded Linux

Re: error while loading state for instance 0x0 of device 'kvmclock'

[Marcelo Tosatti]

On Mon, Nov 02, 2009 at 11:28:38AM +0100, Jan Kiszka wrote:
> Jan Kiszka wrote:
> > Hi,
> > 
> > current qemu-kvm.git gives me the message "qemu: warning: error while
> > loading state for instance 0x0 of device 'kvmclock'" when I run a simple
> > "savevm" followed by a "loadvm 1". What's broken here?
> 
> OK, this is due to "KVM: add flags to kvm_clock_data" (958b0c5497): the
> flags field is not cleared on KVM_SET_CLOCK. Will post a fix.
> 
> But the above kernel commit is also broken: KVM_GET_CLOCK checks
> uninitialized user_ns.flags (probably instead of the user's value). This
> raises the question if the caller of KVM_GET_CLOCK is also supposed to
> pass kvm_clock_data with flags cleared down to the kernel. Could someone
> clarify this so I could fix it accordingly?

Yes userspace is supposed to clear flags. My bad.

Re: error while loading state for instance 0x0 of device 'kvmclock'

[Avi Kivity]

On 11/02/2009 12:28 PM, Jan Kiszka wrote:
> Jan Kiszka wrote:
>    
>> Hi,
>>
>> current qemu-kvm.git gives me the message "qemu: warning: error while
>> loading state for instance 0x0 of device 'kvmclock'" when I run a simple
>> "savevm" followed by a "loadvm 1". What's broken here?
>>      
> OK, this is due to "KVM: add flags to kvm_clock_data" (958b0c5497): the
> flags field is not cleared on KVM_SET_CLOCK. Will post a fix.
>
> But the above kernel commit is also broken: KVM_GET_CLOCK checks
> uninitialized user_ns.flags (probably instead of the user's value). This
> raises the question if the caller of KVM_GET_CLOCK is also supposed to
> pass kvm_clock_data with flags cleared down to the kernel. Could someone
> clarify this so I could fix it accordingly?
>    

I'd make KVM_GET_CLOCK set the flags, not get them.  So if we add new 
fields, we just set a new bit and userspace can read it.

-- 
error compiling committee.c: too many arguments to function

Re: error while loading state for instance 0x0 of device 'kvmclock'

[Jan Kiszka]

Avi Kivity wrote:
> On 11/02/2009 12:28 PM, Jan Kiszka wrote:
>> Jan Kiszka wrote:
>>    
>>> Hi,
>>>
>>> current qemu-kvm.git gives me the message "qemu: warning: error while
>>> loading state for instance 0x0 of device 'kvmclock'" when I run a simple
>>> "savevm" followed by a "loadvm 1". What's broken here?
>>>      
>> OK, this is due to "KVM: add flags to kvm_clock_data" (958b0c5497): the
>> flags field is not cleared on KVM_SET_CLOCK. Will post a fix.
>>
>> But the above kernel commit is also broken: KVM_GET_CLOCK checks
>> uninitialized user_ns.flags (probably instead of the user's value). This
>> raises the question if the caller of KVM_GET_CLOCK is also supposed to
>> pass kvm_clock_data with flags cleared down to the kernel. Could someone
>> clarify this so I could fix it accordingly?
>>    
> 
> I'd make KVM_GET_CLOCK set the flags, not get them.  So if we add new 
> fields, we just set a new bit and userspace can read it.

This makes sense and actually fixes the issue completely. Patch on its
way...

Jan

-- 
Siemens AG, Corporate Technology, CT SE 2
Corporate Competence Center Embedded Linux

Re: error while loading state for instance 0x0 of device 'kvmclock'

[Glauber Costa]

On Mon, Nov 02, 2009 at 04:37:15PM +0100, Jan Kiszka wrote:
> Avi Kivity wrote:
> > On 11/02/2009 12:28 PM, Jan Kiszka wrote:
> >> Jan Kiszka wrote:
> >>    
> >>> Hi,
> >>>
> >>> current qemu-kvm.git gives me the message "qemu: warning: error while
> >>> loading state for instance 0x0 of device 'kvmclock'" when I run a simple
> >>> "savevm" followed by a "loadvm 1". What's broken here?
> >>>      
> >> OK, this is due to "KVM: add flags to kvm_clock_data" (958b0c5497): the
> >> flags field is not cleared on KVM_SET_CLOCK. Will post a fix.
> >>
> >> But the above kernel commit is also broken: KVM_GET_CLOCK checks
> >> uninitialized user_ns.flags (probably instead of the user's value). This
> >> raises the question if the caller of KVM_GET_CLOCK is also supposed to
> >> pass kvm_clock_data with flags cleared down to the kernel. Could someone
> >> clarify this so I could fix it accordingly?
> >>    
> > 
> > I'd make KVM_GET_CLOCK set the flags, not get them.  So if we add new 
> > fields, we just set a new bit and userspace can read it.
> 
> This makes sense and actually fixes the issue completely. Patch on its
> way...
agreed. This is the best behaviour I can devise, indeed.