On 2013-03-06 22:30, Marcelo Tosatti wrote: > On Wed, Mar 06, 2013 at 08:57:54AM +0100, Jan Kiszka wrote: >> On 2013-03-06 07:12, Paolo Bonzini wrote: >>> >>>> On Tue, Mar 05, 2013 at 08:16:41PM -0300, Marcelo Tosatti wrote: >>>>> On Mon, Mar 04, 2013 at 10:41:43PM +0100, Jan Kiszka wrote: >>>>>> From: Jan Kiszka <jan.kiszka@xxxxxxxxxxx> >>>>>> >>>>>> A VCPU sending INIT or SIPI to some other VCPU races for setting >>>>>> the >>>>>> remote VCPU's mp_state. When we were unlucky, >>>>>> KVM_MP_STATE_INIT_RECEIVED >>>>>> was overwritten by kvm_emulate_halt and, thus, got lost. >>>>>> >>>>>> Fix this by raising requests on the sender side that will then be >>>>>> handled synchronously over the target VCPU context. >>>>>> >>>>>> Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx> >>>>> >>>>> Why is kvm_emulate_halt being executed from >>>>> KVM_MP_STATE_INIT_RECEIVED/KVM_MP_STATE_SIPI_RECEIVED again? >>>>> >>>>> Why is it not true that the only valid transition from >>>>> KVM_MP_STATE_HALTED is from KVM_MP_STATE_RUNNABLE? >>>> >>>> See Paolo's table, it is. So why fix a race which should not be >>>> happening in the first place. >>> >>> The bad transition happens exactly because of the race. >>> Are you saying you prefer the solution with cmpxchg? >> >> I think we are past that point in our discussion and should really >> separate signal (INIT/SIPI) from state (INIT/SIPI_RECEIVED etc.). >> >> Jan > > The sentence "KVM_MP_STATE_INIT_RECEIVED overwritten by > kvm_emulate_halt" is contradictory, unless i miss something. http://thread.gmane.org/gmane.comp.emulators.kvm.devel/105638 Jan
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