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[Qemu-devel] Re: [PATCH v2 14/21] qemu-kvm: Rework VCPU state writeback

From: Avi Kivity
Subject: [Qemu-devel] Re: [PATCH v2 14/21] qemu-kvm: Rework VCPU state writeback API
Date: Sun, 07 Feb 2010 15:34:56 +0200
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On 02/03/2010 10:53 AM, 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_ASYNC_STATE (during runtime, other VCPUs continue to run)

Wouldn't that be SYNC_STATE (state that is modified by the current vcpu only)?

- 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. It does
not touch qemu-kvm's special hooks for mpstate, vcpu_events, or tsc
loading. They will be cleaned up by individual patches.

I'm uneasy about this. What are the rules for putting cpu_synchronize_state() now?

error compiling committee.c: too many arguments to function

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