From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 2/2][RFC] KVM: Emulate MSI-X table and PBA in kernel Date: Thu, 30 Dec 2010 12:37:18 +0200 Message-ID: <4D1C60DE.4020800@redhat.com> References: <1293007495-32325-1-git-send-email-sheng@linux.intel.com> <201012291655.19535.sheng@linux.intel.com> <20101229092824.GA2876@redhat.com> <201012301532.42341.sheng@linux.intel.com> <20101230074748.GB7889@redhat.com> <4D1C5124.2090409@redhat.com> <20101230103256.GB6441@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Sheng Yang , Marcelo Tosatti , kvm@vger.kernel.org, Alex Williamson To: "Michael S. Tsirkin" Return-path: Received: from mx1.redhat.com ([209.132.183.28]:54485 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752093Ab0L3KhX (ORCPT ); Thu, 30 Dec 2010 05:37:23 -0500 In-Reply-To: <20101230103256.GB6441@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 12/30/2010 12:32 PM, Michael S. Tsirkin wrote: > On Thu, Dec 30, 2010 at 11:30:12AM +0200, Avi Kivity wrote: > > On 12/30/2010 09:47 AM, Michael S. Tsirkin wrote: > > >I am not really suggesting this. What I say is PBA is unimplement= ed > > >let us not commit to an interface yet. > > > > What happens to a guest that tries to use PBA? > > It's a mandatory part of MSI-X, no? > > Yes. Unfortunately the pending bit is in fact a communication channel > used for function specific purposes when mask bit is set, > and 0 when unset. The spec even seems to *require* this use: > > I refer to this: > > For MSI and MSI-X, while a vector is masked, the function is prohibi= ted > from sending the associated message, and the function must set the > associated Pending bit whenever the function would otherwise send th= e > message. When software unmasks a vector whose associated Pending bit= is > set, the function must schedule sending the associated message, and > clear the Pending bit as soon as the message has been sent. Note tha= t > clearing the MSI-X Function Mask bit may result in many messages nee= ding > to be sent. > > > If a masked vector has its Pending bit set, and the associated > underlying interrupt events are somehow satisfied (usually by softwa= re > though the exact manner is function-specific), the function must cle= ar > the Pending bit, to avoid sending a spurious interrupt message later > when software unmasks the vector. However, if a subsequent interrupt > event occurs while the vector is still masked, the function must aga= in > set the Pending bit. > > > Software is permitted to mask one or more vectors indefinitely, and > service their associated interrupt events strictly based on polling > their Pending bits. A function must set and clear its Pending bits a= s > necessary to support this =E2=80=9Cpure polling=E2=80=9D mode of ope= ration. > > For assigned devices, supporting this would require > that the mask bits on the device are set if the mask bit in > guest is set (otherwise pending bits are disabled). Can't this be done by setting the real mask bit when the guest reads th= e=20 virtual pending bit, then reading the real pending bit? > Existing code does not support PBA in assigned devices, so at least i= t's > not a regression there, and the virtio spec says nothing about this s= o > we should be fine. Why isn't it subject to the pci spec? If an interrupt condition exits, the bit should be set. --=20 error compiling committee.c: too many arguments to function