On Thu, Sep 24, 2009 at 10:53:59AM +0300, Avi Kivity wrote: > On 09/23/2009 06:45 PM, Jan Kiszka wrote: > >>Functions calling each other in the same subsystem can rely on callers > >>calling cpu_synchronize_state(). Across subsystems, that's another > >>matter, exported functions should try not to rely on implementation > >>details of their callers. > >> > >>(You might argue that the apic is not separate subsystem wrt an x86 cpu, > >>and I'm not sure I have a counterargument) > >> > >I do accept this argument. It's just that my feeling is that we are > >lacking proper review of the required call sites of cpu_sychronize_state > >and rather put it where some regression popped up (and that only in > >qemu-kvm...). > > That's life... > > >The new rule is: Synchronize the states before accessing registers (or > >in-kernel devices) the first time after a vmexit to user space. > > No, the rule is: synchronize state before accessing registers. > Extra synchronization is cheap, while missing synchronization is > very expensive. > So should we stick cpu_synchronize_state() before each register accesses? I think it is reasonable to omit it if all callers do it already. > >But, > >e.g., I do not see where we do this on CPU reset. > > That's a bug. > Only if kvm support cpus without apic. Otherwise CPU is reset by apic_reset() and cpu_synchronize_state() is called there. -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
