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

[Marcelo Tosatti <mtosatti@redhat.com>]

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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.


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