From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andre Przywara Subject: Re: [RFC v7 1/7] KVM: api: pass the devid in the msi routing entry Date: Thu, 21 Jul 2016 17:43:41 +0100 Message-ID: <6c971903-1158-e450-f41c-665dd4ba660e@arm.com> References: <1468848357-2331-1-git-send-email-eric.auger@redhat.com> <1468848357-2331-2-git-send-email-eric.auger@redhat.com> <20160721160124.GB32739@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?= , Eric Auger Return-path: Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:56533 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753267AbcGUQmy (ORCPT ); Thu, 21 Jul 2016 12:42:54 -0400 In-Reply-To: <20160721160124.GB32739@potion> Sender: kvm-owner@vger.kernel.org List-ID: 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 >> >> --- >> >> v6 -> v7: >> - Added Andre's R-b >> >> v4 -> v5: >> - some rephrasing in api.txt according to Christoffer's comments >> v2 -> v3: >> - replace usage of KVM_IRQ_ROUTING_EXTENDED_MSI type by >> usage of KVM_MSI_VALID_DEVID flag >> - add note about KVM_CAP_MSI_DEVID capability >> >> v1 -> v2: >> - devid id passed in kvm_irq_routing_msi instead of in >> kvm_irq_routing_entry >> >> RFC -> PATCH >> - remove kvm_irq_routing_extended_msi and use union instead >> --- >> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtu= al/kvm/api.txt >> @@ -1479,9 +1483,20 @@ struct kvm_irq_routing_msi { >> __u32 address_lo; >> __u32 address_hi; >> __u32 data; >> - __u32 pad; >> + union { >> + __u32 pad; >> + __u32 devid; >> + }; >> }; >> =20 >> +devid: If KVM_MSI_VALID_DEVID is set, contains a unique device iden= tifier >> + for the device that wrote the MSI message. >> + For PCI, this is usually a BFD identifier in the lower 16 bi= ts. >> + >> +The per-VM KVM_CAP_MSI_DEVID capability advertises the requirement = to >> +provide the device ID. If this capability is not set, userland cann= ot >> +rely on the kernel to allow the KVM_MSI_VALID_DEVID flag being set. >=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 m= ake > it depend only on the presence of KVM_CAP_MSI_DEVID, like the patch d= oes > 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 enableab= le, > so does enabling KVM_CAP_MSI_DEVID mean that every MSI must have a va= lid > 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 the CAP because we repurposed the pad field. Does that make sense? Admittedly this _is_ confusing ;-) Cheers, Andre. >=20 > Thanks. >=20 > --- > I'm confused about the purpose behind two dynamic flags that seem to = do > that same thing, but those are just nitpicks, the API looks good in > general. >=20