On 03.12.14 04:48, Paul Mackerras wrote: > When a secondary hardware thread has finished running a KVM guest, we > currently put that thread into nap mode using a nap instruction in > the KVM code. This changes the code so that instead of doing a nap > instruction directly, we instead cause the call to power7_nap() that > put the thread into nap mode to return. The reason for doing this is > to avoid having the KVM code having to know what low-power mode to > put the thread into. > > In the case of a secondary thread used to run a KVM guest, the thread > will be offline from the point of view of the host kernel, and the > relevant power7_nap() call is the one in pnv_smp_cpu_disable(). > In this case we don't want to clear pending IPIs in the offline loop > in that function, since that might cause us to miss the wakeup for > the next time the thread needs to run a guest. To tell whether or > not to clear the interrupt, we use the SRR1 value returned from > power7_nap(), and check if it indicates an external interrupt. We > arrange that the return from power7_nap() when we have finished running > a guest returns 0, so pending interrupts don't get flushed in that > case. > > Note that it is important a secondary thread that has finished > executing in the guest, or that didn't have a guest to run, should > not return to power7_nap's caller while the kvm_hstate.hwthread_req > flag in the PACA is non-zero, because the return from power7_nap > will reenable the MMU, and the MMU might still be in guest context. > In this situation we spin at low priority in real mode waiting for > hwthread_req to become zero. > > Signed-off-by: Paul Mackerras <paulus@xxxxxxxxx> > --- > I think this would be best going through the powerpc tree. Alex, > if you can give me an acked-by for this that would be appreciated. Acked-by: Alexander Graf <agraf@xxxxxxx> Alex -- 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
