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

[Marcelo Tosatti]

On Tue, Mar 02, 2010 at 09:00:04AM +0100, Jan Kiszka wrote:
> 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 <address@hidden>
> > 
> > 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...

No issues with qemu-kvm. Could not spot anything obvious.

> 
> Jan
>