From mboxrd@z Thu Jan 1 00:00:00 1970 From: Radim =?utf-8?B?S3LEjW3DocWZ?= Subject: Re: [RFC v7 1/7] KVM: api: pass the devid in the msi routing entry Date: Thu, 21 Jul 2016 19:15:14 +0200 Message-ID: <20160721171514.GF32739@potion> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Eric Auger , 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: Andre Przywara Return-path: Received: from mx1.redhat.com ([209.132.183.28]:45188 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753153AbcGURPU (ORCPT ); Thu, 21 Jul 2016 13:15:20 -0400 Content-Disposition: inline In-Reply-To: <6c971903-1158-e450-f41c-665dd4ba660e@arm.com> Sender: kvm-owner@vger.kernel.org List-ID: 2016-07-21 17:43+0100, Andre Przywara: > Hi Radim, >=20 > 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 ide= ntifier >>> + for the device that wrote the MSI message. >>> + For PCI, this is usually a BFD identifier in the lower 16 b= its. >>> + >>> +The per-VM KVM_CAP_MSI_DEVID capability advertises the requirement= to >>> +provide the device ID. If this capability is not set, userland can= not >>> +rely on the kernel to allow the KVM_MSI_VALID_DEVID flag being set= =2E >>=20 >> 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.) >>=20 >> Then there would be little point in having KVM_CAP_MSI_DEVID enablea= ble, >> so does enabling KVM_CAP_MSI_DEVID mean that every MSI must have a v= alid >> devid? >=20 > KVM_CAP_MSI_DEVID tells userland that it's fine to set the > KVM_MSI_VALID_DEVID flag (because the kernel would bark otherwise). >=20 > KVM_MSI_VALID_DEVID tells the kernel that there is some meaningful > device ID data in the field formerly known as "pad". >=20 > IIRC we started with the VALID_DEVID flag, then found that we need th= e > CAP because we repurposed the pad field. >=20 > Does that make sense? Admittedly this _is_ confusing ;-) It does, thanks. Some capability is need and I thought that KVM_CAP_MSI_DEVID has to be enabled by userspace before KVM_MSI_VALID_DEVID can be used, which isn'= t the case. It is enabled conditionally based on vgic ITS ... my bad.