From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH v2 14/21] qemu-kvm: Rework VCPU state writeback API Date: Sun, 07 Feb 2010 15:34:56 +0200 Message-ID: <4B6EC180.7000203@redhat.com> References: <4822161334c3e10d7772dbd08dafdd3a78c86ce4.1265187223.git.jan.kiszka@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Marcelo Tosatti , kvm@vger.kernel.org, Anthony Liguori , Alexander Graf , Glauber Costa , qemu-devel@nongnu.org To: Jan Kiszka Return-path: Received: from mx1.redhat.com ([209.132.183.28]:51000 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751007Ab0BGNfF (ORCPT ); Sun, 7 Feb 2010 08:35:05 -0500 In-Reply-To: <4822161334c3e10d7772dbd08dafdd3a78c86ce4.1265187223.git.jan.kiszka@siemens.com> Sender: kvm-owner@vger.kernel.org List-ID: 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 > 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? -- error compiling committee.c: too many arguments to function