Avi Kivity wrote: > 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)? It's async /wrt other VCPUs. They continue to run and may interact with this VCPU while updating its state. > >> - 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. 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? As before for code that accesses the state during runtime: Before you read or write some bit of it, call cpu_synchronize_state(). Only reset and save/restore handlers do not have to worry about synchronization anymore. It makes no sense to overload them with arch-specific KVM knowledge about what shall be written and when. Jan
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