From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [IPv6:2401:3900:2:1::2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id E225D1A0549 for ; Wed, 17 Dec 2014 23:40:50 +1100 (AEDT) Received: from mx2.suse.de (cantor2.suse.de [195.135.220.15]) (using TLSv1 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 6352E1401DC for ; Wed, 17 Dec 2014 23:40:50 +1100 (AEDT) Message-ID: <549179CE.7030100@suse.de> Date: Wed, 17 Dec 2014 13:40:46 +0100 From: Alexander Graf MIME-Version: 1.0 To: Paul Mackerras , linuxppc-dev@ozlabs.org Subject: Re: [PATCH] powerpc: powernv: Return to cpu offline loop when finished in KVM guest References: <20141203034840.GA612@iris.ozlabs.ibm.com> In-Reply-To: <20141203034840.GA612@iris.ozlabs.ibm.com> Content-Type: text/plain; charset=windows-1252 Cc: kvm@vger.kernel.org, kvm-ppc@vger.kernel.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 > --- > 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 Alex