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

From: Avi Kivity
Subject: [Qemu-devel] Re: [PATCH 2/4] KVM: Rework VCPU state writeback API
Date: Thu, 11 Mar 2010 10:32:50 +0200
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20100301 Fedora/3.0.3-1.fc12 Thunderbird/3.0.3

On 03/02/2010 02:14 AM, 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

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>

This patch breaks system reset of WinXP.32 install (more easily
reproducible without iothread enabled).

What's the conclusion here?  The patch is innocent of the regression?

error compiling committee.c: too many arguments to function

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