From mboxrd@z Thu Jan 1 00:00:00 1970 From: Auger Eric Subject: Re: [RFC v7 1/7] KVM: api: pass the devid in the msi routing entry Date: Thu, 21 Jul 2016 22:48:48 +0200 Message-ID: References: <1468848357-2331-1-git-send-email-eric.auger@redhat.com> <1468848357-2331-2-git-send-email-eric.auger@redhat.com> <20160721160124.GB32739@potion> <6c971903-1158-e450-f41c-665dd4ba660e@arm.com> <20160721171514.GF32739@potion> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: eric.auger.pro@gmail.com, marc.zyngier@arm.com, christoffer.dall@linaro.org, drjones@redhat.com, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, pbonzini@redhat.com To: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Andre Przywara Return-path: Received: from mx1.redhat.com ([209.132.183.28]:44435 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753968AbcGUUsw (ORCPT ); Thu, 21 Jul 2016 16:48:52 -0400 In-Reply-To: <20160721171514.GF32739@potion> Sender: kvm-owner@vger.kernel.org List-ID: Hi, On 21/07/2016 19:15, Radim Kr=C4=8Dm=C3=A1=C5=99 wrote: > 2016-07-21 17:43+0100, Andre Przywara: >> Hi Radim, >> >> On 21/07/16 17:01, Radim Kr=C4=8Dm=C3=A1=C5=99 wrote: >>> 2016-07-18 13:25+0000, Eric Auger: >>>> On ARM, the MSI msg (address and data) comes along with >>>> out-of-band device ID information. The device ID encodes the >>>> device that writes the MSI msg. Let's convey the device id in >>>> kvm_irq_routing_msi and use KVM_MSI_VALID_DEVID flag value in >>>> kvm_irq_routing_entry to indicate the msi devid is populated. >>>> >>>> Signed-off-by: Eric Auger >>>> Reviewed-by: Andre Przywara >>>> >>>> --- >>>> =20 >>>> +devid: If KVM_MSI_VALID_DEVID is set, contains a unique device id= entifier >>>> + for the device that wrote the MSI message. >>>> + For PCI, this is usually a BFD identifier in the lower 16 = bits. >>>> + >>>> +The per-VM KVM_CAP_MSI_DEVID capability advertises the requiremen= t to >>>> +provide the device ID. If this capability is not set, userland ca= nnot >>>> +rely on the kernel to allow the KVM_MSI_VALID_DEVID flag being se= t. >>> >>> It would be better to enforce this mentioned dependency on set >>> KVM_CAP_MSI_DEVID, but is the dependency even required? >>> It seems we were checking flags for zero, so KVM_MSI_VALID_DEVID >>> couldn't have been set by old userspaces, therefor it is ok to only= make >>> it depend only on the presence of KVM_CAP_MSI_DEVID, like the patch= does >>> now. (I assume KVM_MSI_VALID_DEVID and KVM_CAP_MSI_DEVID are being >>> merged at the same time.) >>> >>> Then there would be little point in having KVM_CAP_MSI_DEVID enable= able, >>> so does enabling KVM_CAP_MSI_DEVID mean that every MSI must have a = valid >>> devid? >> >> KVM_CAP_MSI_DEVID tells userland that it's fine to set the >> KVM_MSI_VALID_DEVID flag (because the kernel would bark otherwise). >> >> KVM_MSI_VALID_DEVID tells the kernel that there is some meaningful >> device ID data in the field formerly known as "pad". >> >> IIRC we started with the VALID_DEVID flag, then found that we need t= he >> CAP because we repurposed the pad field. >> >> Does that make sense? Admittedly this _is_ confusing ;-) >=20 > It does, thanks. > Some capability is need and I thought that KVM_CAP_MSI_DEVID has to b= e > enabled by userspace before KVM_MSI_VALID_DEVID can be used, which is= n't > the case. It is enabled conditionally based on vgic ITS ... my bad. >=20 Great Thanks Andre for the clarification Eric