[Qemu-devel] Re: [PATCH 2/4] KVM: Rework VCPU state writeback API

[Jan Kiszka <jan.kiszka@web.de>]

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Marcelo Tosatti wrote:
> On Mon, Mar 01, 2010 at 07:10:30PM +0100, Jan Kiszka wrote:
>> This grand cleanup drops all reset and vmsave/load related
>> synchronization points in favor of four(!) generic hooks:
>>
>> - cpu_synchronize_all_states in qemu_savevm_state_complete
>>   (initial sync from kernel before vmsave)
>> - cpu_synchronize_all_post_init in qemu_loadvm_state
>>   (writeback after vmload)
>> - cpu_synchronize_all_post_init in main after machine init
>> - cpu_synchronize_all_post_reset in qemu_system_reset
>>   (writeback after system reset)
>>
>> These writeback points + the existing one of VCPU exec after
>> cpu_synchronize_state map on three levels of writeback:
>>
>> - KVM_PUT_RUNTIME_STATE (during runtime, other VCPUs continue to run)
>> - KVM_PUT_RESET_STATE   (on synchronous system reset, all VCPUs stopped)
>> - KVM_PUT_FULL_STATE    (on init or vmload, all VCPUs stopped as well)
>>
>> This level is passed to the arch-specific VCPU state writing function
>> that will decide which concrete substates need to be written. That way,
>> no writer of load, save or reset functions that interact with in-kernel
>> KVM states will ever have to worry about synchronization again. That
>> also means that a lot of reasons for races, segfaults and deadlocks are
>> eliminated.
>>
>> cpu_synchronize_state remains untouched, just as Anthony suggested. We
>> continue to need it before reading or writing of VCPU states that are
>> also tracked by in-kernel KVM subsystems.
>>
>> Consequently, this patch removes many cpu_synchronize_state calls that
>> are now redundant, just like remaining explicit register syncs.
>>
>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> 
> Jan,
> 
> This patch breaks system reset of WinXP.32 install (more easily
> reproducible without iothread enabled).
> 
> Screenshot attached.
> 

Strange - no issues with qemu-kvm? Any special command line switch? /me
goes scrounging for some installation XP32 CD in the meantime...

Jan


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